JP2014039958A - Coagulation microstructure of molding mold molded by aggregate-using casting mold - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a molding metal mold molded by an aggregate-using casting mold for indicating an area of a precise coagulation microstructure in a wide range of the mold.SOLUTION: The molding metal mold molded by the aggregate-using casting mold is a metal mold for indicating a molding microstructure composed of an alloy including aluminum by a quick chilling process in the casting mold including an aggregate, and the microstructure is composed of a first area where the microstructure is positioned in the vicinity of a surface of the metal mold, that is, the first area having a rough coagulation microstructure and a second area positioned inside the first area, that is, the second area having the precise coagulation microstructure, and the first area includes dendrite having a dendrite arm separated at an interval of 20-200 micrometers, and the second area includes the dendrite having the dendrite arm separated at an interval of 5-15 micrometers.

Description

  The present invention relates to a metal molded article (metal cast article), and in particular, a shaped metal casting having a fine solidification microstructure formed by a casting method including an aggregate. )

  In the conventional casting method, molten metal is poured into a mold and solidified or solidified by heat loss of the mold. When a sufficient amount of heat is released for the cooling, the final product, that is, the molded product (cast product) can support its own weight. The molded product is then removed from the mold.

  Different types of molds of the prior art each have a certain effect. For example, green sand molds consist of aggregate and sand, which are bonded and hardened by a binder such as a mixture of clay and water. These molds can be made quickly, for example, simple molds can be made in 10 seconds in an automated mold production plant. In addition, the sand can be recycled relatively easily.

  As other sand molds, resin-based chemical binders having high dimensional precision and high hardness are often used. Such a resin-molded sand mold is slightly longer than a fresh sand mold. This is because a curing reaction always occurs and the binder exhibits an effect to promote the formation of the mold. In a mold using viscosity adhesion, sand is often recycled although it requires resin removal treatment.

  In addition to making relatively quick and economical, sand molds also have high productivity. The sand mold is removed after casting metal is poured and cooled and solidified, and another mold is poured.

  The sand used as sand aggregate in sand molds is most commonly silica. However, other minerals are used to avoid the undesirable transition from alpha quartz to beta quartz at about 570 degrees Celsius (° C.) or about 1058 degrees Fahrenheit (° F.), including meteorites, chromium steels And zircon. These sands show small differences in thermal conductivity from typical silica sands, and in some cases silica sands or mixed with each other in molds or core pieces attempt to achieve directional solidification, and Facilitate. These minerals have certain drawbacks. Meteorites are often susceptible to chemical changes and cause problems of uniform control by chemical binders. Also, chromite is usually crushed, producing sharp grains that lead to poor surface finish of molded parts and rapid wear of machinery. Zircon is heavy and increases the demands on equipment used to form and manage molds, causing rapid wear of machinery. Mixing these sands as a different configuration of a simple mold also exacerbates the results of sand recycling.

  In addition, the disadvantages arising from the unique aspects of silica, its alternative minerals, clay-based sand molds and chemical binders are usually due to their relatively low thermal conductivity, which usually causes quenching of the cast metal. It is impossible. Rapid cooling of the cast metal is often desirable and techniques are known in which such cooling improves the mechanical properties of the molded article. In addition, quenching can maintain further mixing of the components, resulting in the possibility of omitting subsequent dissolution processing, saving time and money. Omission of the melting process typically avoids the need for subsequent quenching and can eliminate the distortion and residual stress problems of the molded product caused by quenching. In relation to mechanical properties, the fineness of the cast microstructure is related to the degree of cooling and solidification. Generally, as the degree of cooling and solidification increases, the solidification microstructure of the molded product becomes finer (fine).

  As an alternative to sand molds, molds made from metal or semi-permanent molds or chill metal molds are sometimes used. Due to their relatively high thermal conductivity, these metal molds are particularly advantageous in order to rapidly cool and solidify the cast molten metal, which in turn provides an advantage in the mechanical properties of the molded part. For example, a particular casting method known as pressure die casting is used for metal molds and is known to have a rapid solidification rate. Such rapid solidification rate is indicated by the presence of fine dendrite arm spacing (DAS) in the molded part. As is well known in the art, as the solidification rate increases, the DAS decreases. However, since extreme surface turbulence occurs in the molten metal while filling the mold, the pressure die casting method often forms defects in the cast part. Fine dendrite arm spacing can also be formed by cooling the molded article with local chillers or fins. Such techniques include the local use of solid chiller components, such as metal mass chillers or castable chiller assemblies, and the like, which are in the vicinity of the cooling part of the mold. It is captured. However, these methods only give a local effect in the area where the chill is applied. This local effect is in contrast to the effect of the present invention, where the advantages of a fine microstructure are obtained when the present invention is accurately and extensively implemented on molded articles. This is an important aspect of the present invention. Because the greatest effect is that the molded product not only has a high quality in general throughout the product, but also shows the characteristic that it is essentially uniform. Because it gives to. Thus, the product according to the invention essentially enjoys the uniformity normally found in forgings.

  One type of known permanent mold method that provides for rapid cooling of the residual liquid phase in the structure includes semi-solid casting. In this method, the metal slurry consists of dendritic fragments formed outside the mold and suspended in the residual liquid phase. The transfer of the mixture to the metal die rapidly solidifies the remaining liquid, giving a dense structure, but surrounded by relatively coarsely separated dendrites (dendrites), degenerate dendrites (dendrites), Often in the form of a rose knot or baby boom.

  However, all molds made from metal have significant economic disadvantages. Since the molded product needs to solidify before being removed from the mold, it is necessary to use multiple metal molds to achieve high productivity. The need for multiple molds in permanent molds increases the cost of mechanical equipment and typically increases the cost of mechanical equipment at least five times over sand molds.

  Another common feature of the internal structure of conventional shaped articles is a region that exhibits a larger geometric factor (ie, cooling That is, the region having a larger volume fraction) generally has a coarser structure. Such areas in molded articles usually have much lower mechanical properties. In addition, such regions typically exhibit cavities or pores that cause shrinkage. Because they are more easily separated from the feed metal later in solidification. Such regions are often found, for example, in hot spots formed by protrusions separated on a relatively thin plate. Complex molded products are often full of such features, preventing the uniformization of various properties. The problem complicates the work of product designers. For example, thickening the cross section to increase the strength weakens various characteristics and, in the worst case, causes a defect, which increases the uncertainty and often has the opposite effect.

In places where solidification of molded products is slow, (i) not only has a rough structure (characterized by a rough DAS), but also (ii) exhibits porosity and (iii) is generally harmful to aluminum alloys with iron as an impurity However, large plate crystals composed of iron-rich phases can be formed. All these elements have produced very fine cast microstructures, which are very detrimental to the ductility of the alloy, in various scientific studies as interesting research subjects in the laboratory. (For example, the research paper by GS Reddy and JA Sekhar inActa Metallurgica, 1989, vol. 37, Number 5, pp. 1509-1519 and the research paper by L. Snugovsky, JF Major, DD Perovic and JW Rutter; "Silicon segregation in aluminum casting alloy ”Materials Science and Technology 2000 16 125-128.).
However, in contrast to such laboratory studies, the invention described in the present invention provides unique conditions, and according to these conditions, the solidification microstructure described previously in this specification. (Solidification microstructure) is constantly generated, and the manufacturing process can be operated so that a three-dimensional molded product (cast product) can be produced in a single generation or mass production.

  It is generally not well known that the interior of a molded product is frozen at an accelerated rate as a result of the geometric effects of the shaped product (molded product). The initial solidification near the surface of the molded article is substantially constant and usually changes at a rate that increases parabolically over time; that is, the solidification rate increases with the thickness of the solidified layer. As you do, the speed decreases. In contrast, the volume of residual liquid in the center of the molded part gradually decreases with time and undergoes an increasing amount of heat released from a new direction, so that the solidification rate increases considerably. This effect has been described in detail by one of the inventors. Castings, John Campbell, pp. 125-126 (2nd Edition, 2003), which is published in Butterworth Heinemann, Oxford, England, and is incorporated by reference in its entirety. The behavior is explained by the so-called reverse chill effect of the cast iron molded product, and the central part of the molded product does not seem to be well explained, but it may show color and solidify in appearance, and gray to cool. Contrast with the outer area of the slower molded product.

  As a result, it is desirable to develop a casting method and related equipment that has the advantage of being able to solidify rapidly like a metal mold, while being less expensive, more productive and recyclable like a sand mold. .

  In addition, in order to promote substantially uniform properties similar to forgings, we provide shaped molded products molded with aggregate molds that show areas of fine (fine) solidification microstructures over a wide range of molded products. It is also desirable to do. (Since the various characteristics are relatively unaffected by changes in the cooling rate at the high cooling rate used in the present invention, the changes described later (for example, shown in FIG. 4) do not significantly affect the various characteristics. Substantially uniform the various properties of the cast product.) Especially finer than the structure produced by the conventional aggregate casting method, if possible finer than that produced by permanent mold It is desired to provide a shaped molded article molded with an aggregate-use mold having a microstructure.

  In addition, the molding formed by an aggregate-use mold having a fine microstructure region that is substantially continuous from the distal end of the molded article to the feeder or feeder (proximal end). It is desirable to provide goods.

  The present invention is a shaped metal molded product formed of aggregate by an ablation casting method, than a similar metal having a similar mass or cross-sectional thickness generated by a shaped casting method including a conventional aggregate. Disclosed is a shaped metal molded article that includes a finely solidified microstructure, wherein the solidified microstructure is composed of one or more grains, dendrites, eutectic phases, or any combination thereof.

  Furthermore, the present invention is a metal molded product formed by a rapid cooling process in a mold containing aggregate and showing a molded microstructure, and the microstructure is a first region located in the vicinity of the surface of the metal molded product. Thus, a metal molded article comprising a first region having a rough solidified microstructure and a second region located inside the first region and having a fine solidified microstructure region is disclosed.

  In a further aspect, the present invention is a metal molded article formed of an alloy containing a eutectic mixture, comprising a double solidified microstructure region, wherein the double solidified microstructure region is (i) 1 or more. And (ii) one or more fine eutectic parts.

  In addition, the present invention is a shaped metal molded article casting that is at least partially made of an aggregate mold, the molded article including a double solidified microstructure region, wherein the double solidified microstructure region is At least one coarsely solidified microstructure part having a particle size and / or dendrite arm and / or a eutectic width in the range normally expected in a conventional aggregate or metal mold, At least one finely-solidified microstructure part having a particle size of less than 1/3 of the conventional width and / or a dendrite arm and / or a eutectic width in a part of the molding; Disclosed is a molded metal molding casting having:

  In yet another aspect, the present invention is a shaped metal molded article comprising aggregate and shaped by a mold, comprising a double solidified microstructure region, wherein the double solidified microstructure region is about 50 At least one coarsely solidified microstructure portion having a dendrite arm having a dendrite arm spaced from the micrometer by about 200 micrometers; and a dendrite having a dendrite arm spaced by less than about 15 micrometers A shaped metal molded article comprising at least one finely solidified microstructured portion having

  In another aspect, a molded metal molded article formed by an aggregate by an ablation casting method and having a similar metal having a similar mass or cross-sectional thickness generated by a conventional aggregate molding casting method A shaped metal molded article is disclosed that includes a finely solidified microstructure having a finer dendrite arm spacing than the dendrite arm spacing.

  Further disclosed are shaped metal moldings having various characteristics that are substantially complete, high level, and substantially uniform that are somewhat similar to those associated with forgings.

  Other features and advantages of the molded article according to the present invention will be further understood in the drawings, detailed description, examples and claims.

  The drawings are only used to illustrate various embodiments of the invention and are not intended to limit the embodiments relating to the embodiments.

FIG. 1 shows the cooling curve of a solid solution alloy that undergoes dendritic solidification. FIG. 1A shows a diagram illustrating the relationship between dendrite arm spacing and freezing or clotting rate. FIG. 2 shows a photomicrograph (X200) showing the microstructure of a solid solution alloy cast by a conventional casting method. FIG. 3 shows a photomicrograph of a solid solution alloy containing a finely solidified microstructure region (dual DAS structure) produced by ablation. 4A-4E show schematic views of a metal molded product that includes a finely solidified microstructure region. FIG. 5 shows a cooling curve of a mixed alloy of dendrites (dendrites) and eutectic. FIG. 6 shows a photomicrograph (X200) showing the microstructure of 356 alloy showing coarse eutectic silicon fragments cast by conventional methods. FIG. 7 is a micrograph (in X200) showing an ablation-frozen A356 alloy with fine dendritic material (double DAS structure) and fine eutectic material region in addition to the rough region. ). FIG. 8 shows a photomicrograph (X200) showing a portion of an ablation frozen A356 alloy exhibiting uniform coarse DAS and a uniform fine eutectic phase. FIG. 9 shows a photomicrograph (X200) showing an ablation frozen A356 alloy with fine eutectic regions but somewhat roughened after solution heat treatment. FIG. 10 shows a photomicrograph (X200) showing an ablation frozen A356 alloy with a coarse dendritic microstructure and predominantly fine eutectic microstructures but containing a small amount of coarse eutectic phase. FIG. 11 shows details of the micrograph (X1000) of FIG. 10 at higher magnification. FIG. 12 shows the solidification rate of various portions of a dendritic alloy formed according to an exemplary embodiment. FIG. 13 shows a diagram illustrating the cooling rate of various pieces in a molded article of an exemplary embodiment. FIG. 14 shows a table showing the mechanical properties of various exemplary embodiment molded articles. FIG. 15 shows a bar graph and a table comparing the mechanical properties of metal moldings formed by various casting methods. FIG. 16 is a graph showing the relationship between the cell size and solidification rate of an aluminum alloy dendrite (dendritic crystal). FIG. 17a shows a photomicrograph (X1000) of a conventional cast permanent mold microstructure of an aluminum alloy 2.75 ″ (2.75 inch) diameter block. FIG. 17b is a photomicrograph (X1000) of the same metal microstructure produced by the ablation method of the alloy, showing the start position (first part) of the ablated part. FIG. 17c shows a micrograph (X1000) in the last part of the ablated part. FIG. 18 shows a photograph of an ablation frozen B206 alloy automatic control arm showing the location (indicated by the frame) where the test Tensilver was machined after heat treatment. FIG. 19 shows a table of mechanical properties obtained from very thick pieces of B206 aluminum alloy moldings in certain exemplary embodiments. FIG. 20 shows a table showing literature data on cast ten silver produced by various casting methods for A206. FIG. 21 is a microscope of an as-cast (F-quenched) B206 molded article obtained from the center of the thick section shown in FIG. 18 and having both a coarse resinous substance and a fine dendritic substance (double DAS structure). Show photos.

(Detailed explanation)
The present invention relates to a molded article that has at least a finely solidified microstructure region and is aggregate cast and shaped. The aggregate cast shaped metal molded article according to the present invention includes a solidified microstructure that is finer than the solidified microstructure formed by the conventional aggregate casting method. In some embodiments, an aggregate cast shaped metal molded article according to the present invention has a solidified microstructure that has substantially zero porosity.

  The type or nature of the solidification microstructure varies and depends on the metal and / or alloy that undergoes solidification. Various microstructures include dendrites (dendrites), eutectic phases, grains, and the like. In one embodiment, for example, the shaped article has only one type of microstructure. Moreover, the alloy further exhibits a solidified microstructure that includes one or more different microstructures. For example, in one embodiment, the shaped article exhibits a microstructure that includes a combination of dendrites (dendrites) and grains. In other embodiments, the shaped article exhibits a combination of dendrites (dendrites) and eutectic phases. In yet another embodiment, the shaped article exhibits a combination of dendrites (dendritic crystals), eutectic phases and grains. These embodiments do not limit the embodiments, and other combinations and / or other microstructures are possible.

  The eutectic alloy used in the present invention includes any alloy that forms a eutectic phase including a hypoeutectic, near-eutectic, or supereutectic alloy.

  An aggregate cast shaped metal molded article according to the present invention can be formed by the method described in US Application No. 10 / 614,601 filed on July 7, 2003, the entire contents of which are referred to This is included in the present invention. In general, US Application No. 10 / 614,601 discloses a method for quenching and solidifying aggregate-containing cast shaped articles. The method also removes the template. The process described in US application Ser. No. 10 / 614,601 is referred to herein as “ablation”.

  When solidified by the ablation method, the metal molding exhibits a finer solidification microstructure than a similar metal having a similar mass or cross-sectional thickness produced by a conventional aggregate casting method. Microstructure definition is defined by the size or spacing exhibited by a particular type of microstructure. For example, grain indicates particle size, dendrite (dendritic crystal) indicates dendrite arm spacing, and eutectic phase indicates eutectic spacing.

  FIG. 1 shows the cooling or solidification curve of a solid solution alloy. Solid solution alloys form grains and / or dendrites (dendrites) during solidification. The cooling curve showed the cooling of the solid solution alloy over time from the pouring temperature (Tp) passing through the liquid temperature (TL) to the solid temperature (Ts) at which solidification was completed.

  The cooling of the solid solution type alloy in the conventional aggregate-containing casting is indicated by “abcdef” which is a time / temperature distribution. The total cooling time using the conventional method ranges from minutes to hours, and of course depends on the thickness of the molded product and the rate at which heat is transferred to the molded product. The cooling rate was slow at the liquid temperature (TL) as a result of latent heat generation during the formation of dendrites (dendrites). Solidification was completed at the solid temperature (Ts) and the rate of temperature decrease decreased once the latent heat generation had subsided.

At point “e” in FIG. 1, the rapid solidification was too late, so that no effect could be given to the solidified microstructure. And for example, the cooling profile “el” cannot have any effect on the solidification microstructure and is not included as part of the present invention.
However, a cooling profile such as “el” is commonly used in the casting industry where a molded product is removed from a metal die and placed in water for rapid cooling.

  The solid-state structure of a solid solution alloy usually consists of dendrites (dendrites) that are almost entirely delineated by a negligible thickness of the remaining internal dendritic material. The secondary dendrite arm spacing (often referred to as dendrite arm spacing or DAS in the present invention) is the freezing time, i.e. the temperature at which the molded part is fixed is between the liquid temperature TL and the solid temperature Ts of the alloy. It depends on the clotting time of a certain time. From the time of FIG. 1a, it can be seen that ts = te−tc.

  FIG. 1a schematically illustrates the logarithmic relationship between local DAS and local ts in many common aluminum alloys. The figure shows that to reduce DAS by 10 times, it is necessary to reduce ts by approximately 1000 times. (Unfortunately, such a relationship has not been investigated with respect to grain, eutectic width, and therefore facilitates a clear and quantitative description of these other characteristics of the solidification structure of some alloys. Therefore, the quantitative predictions regarding the ablation structure described in the present invention are directed to DAS, however, it is understood that the same is true for grain size and eutectic width, although not quantitative. Thus, a very large increase in the cooling rate is required to substantially affect the fineness of the solidified microstructure.

  The quantitative correlation illustrated in FIG. 1 is explained in terms of dendrites (dendrites) and dendritic arm spacing, but the same is true for grain size and / or in alloys containing grains and / or eutectic phases. Or it is expected that this applies to the eutectic width.

  In conventional aggregate casting methods, the local solidification time is typically on the order of about 1,000 seconds for aluminum alloy molded articles weighing a few pounds or kilograms. These conventional aggregate casting methods produce DAS with a DAS of about 100 micrometers and occasionally with DAS in a width from about 50 micrometers to about 200 micrometers. In the text, solidified microstructures with DAS greater than 50 micrometers are referred to as “coarse” microstructures. FIG. 2 is a photomicrograph showing the coarse microstructure of solid solution cast alloy A206 (standard Al-4.5 wt% Cu alloy) cast by the conventional method.

  The molded product according to the present invention has a fine (fine) solidification microstructure in at least a part of the molded product. That is, the molded product has a fine solidification microstructure from 0% to a maximum of 100%. In one embodiment, the molded article is substantially free of coarse solidified microstructure and has a fine solidified microstructure of up to 100% continuous in the molded article. In other embodiments, the molded article is located near the surface of the molded article and has a first region having a coarse solidification microstructure of up to 100% and an interior of the first region and up to 100% fine. And a second region having a solidified microstructure. In yet another embodiment, the molded article according to the present invention is continuous or at least substantially continuous and has a distal end to a proximal end, i.e. a feeder or pusher. It has a region that extends toward the end adjacent to the hot water.

  The molded article is located in the vicinity of the surface of the molded article and has a first region having a coarse solidification microstructure of up to 100% and a first region having a fine solidification microstructure of up to 100% located inside the first region. 2 regions. In other embodiments, the molded article has a dual solidified microstructure region between a coarse solidified microstructure region and a fine solidified microstructure region. As used herein, a dual microstructure region is a region that includes a coarse microstructure region interspersed with one or more regions of a fine microstructure. In yet other embodiments, the dual solidification microstructure of the molded article is substantially continuous from the distal end of the molded article to the feeder.

  In general, the dendrite arm spacing depends on the time at which solidification occurs. As shown in FIG. 1A, the logarithmic / logarithmic relationship of the dendrite arm interval to the setting time is linear, for example, an aluminum alloy has a gradient of about 1/3. The graph shows that the interval decreases about 5 times as the setting times each increase 100 times. Thus, a given cast piece of a conventional mold gives a corresponding DAS of 100 micrometers when subjected to 1000 seconds of setting. In the ablation casting technique described in US application Ser. No. 10 / 614,601, similar cast pieces would occur with a local solidification time of only about 10 seconds, giving a dendrite arm spacing of about 20 micrometers. The relationship between interval and clotting time remained constant over all experimental times. FIG. 3 is a photomicrograph showing both the fine solidified microstructure region and the coarse microstructure region.

  FIGS. 4A-4E illustrate various exemplary embodiments of a metal casting that has been finely cast and shaped, including a finely solidified microstructure region.

  FIG. 4A shows an embodiment in which the molded article has a small proportion of fine solidification microstructure. The molded product of FIG. 4A shows a case where a quenching process such as ablation is applied in the casting process. In the molded article of FIG. 4A, solidification may occur prior to rapid cooling (eg, ablation), and the molded article partially has a small geometric coefficient (volume relative to the cooling surface rate) and is conventional. Freeze on. The double solidified microstructure region may occur in a portion solidified before the occurrence of ablation, or may occur in a portion that is liquid when the ablation occurs. Even in embodiments such as FIG. 4A, which are far from optimal application of the present invention because some of the molded parts have solidified prior to the quenching process, it is beneficial to have a small amount of fine solidification microstructure. Obviously, in the conventional process, maintaining a small percentage of residual solution in the metal alloy is particularly difficult to freeze without creating defects, such as shrinkage porosity. However, by applying a rapid cooling technique such as ablation, these regions are changed from defect regions to fine structure regions. The presence of a finer structure in a smaller area gives better mechanical properties compared to the defect area of a molded product that has been solidified as before. Although it is conceivable that the trapping region of the remaining solution shown in FIG. 4A exhibits porosity that causes shrinkage, ablation freezing of the region reduces the amount of shrinkage and makes the trapping region strong and sturdy. Can be substituted. In the solidification microstructure profile of FIG. 4A, the quenching phase is considered to be much slower, closer than but prior to point “e” in the graph of FIG.

  In other embodiments, the aggregate templated molded article has a fine solidified microstructure region and a double solidified microstructure region, wherein the double solidified microstructure region is proximate from the distal end of the molded product. Substantially continuous to the end. The embodiment of FIG. 4B shows an example of an embodiment of a molded article having a double continuous solidified microstructure region that is substantially continuous. The solidification microstructure profile of FIG. 4B can be expected to follow the cooling profile “abcdjk” of FIG. In FIG. 4B, the freezing point reaches and passes through the point where the natural freezing of the shrunken fragments has reached the center. The molded product is frozen from the distal end of the molded product to the central portion by a quenching process such as ablation. If the fine structure region produced by rapid freezing ends where the modulus compression is reached (as in the embodiment of FIG. 4B), the molded product freezes firmly to that point. In the embodiment of FIG. 4B, despite the absence of a double solidification microstructure in the shrunken local region, the rapid local solidification time for the entire remaining part of the molded article results in a substantially precise and robust alloy, A continuous region free of shrinkage defects is generated for the entire remaining part of the product. Thus, by promoting clotting in a directional manner from the distal region of the molded article to the proximal feeder, the more distal region of the molded article has a fine solidification microstructure and machine that cannot be achieved by conventional methods. Shows robustness.

  In the embodiment of FIG. 4C, the molded product has a high proportion of fine solidified microstructure, and the double solidified microstructure region continues through the shrinkage region of the molded product. Such desirable solidification microstructure can be reached 1 hour faster than that shown in FIG. 4B by applying a quenching process such as ablation. In other embodiments, as shown in FIG. 4D, the metal molding includes a desired finely-solidified microstructure region that is substantially continuous from the distal end of the molding to the feeder. Such a solidification microstructure can be achieved by applying a rapid quenching process early in the cooling profile. In this embodiment, the molded article can also include a double solidified microstructure region and a coarse solidified microstructure region. The solidification microstructure profile of FIGS. 4C and 4D is believed to be achievable by applying the quenching process early, in which the narrowest part of the molded part is between c and d in the cooling profile of FIG. Follow the route starting at.

In yet another embodiment, as shown in FIG. 4E, the entire solidification microstructure has a fine solidification microstructure. Such a desirable structure can be achieved by applying a quench process to point “b” in the cooling curve of FIG. 1 and following the profile “abghi”. This is thought to be possible if freezing is not caused by heat loss of the mold, and if freezing occurs all at a high rate in a certain direction. However, such a structure is not easily achieved and has not yet been experimentally achieved by the inventors. The difficulty in achieving the solidification microstructure arises from the direct impact of the coolant on the surface of the liquid molding. A molded product with a 100% fine solidification microstructure can be achieved under certain conditions, for example, by using a highly insulating mold or by applying a solidification process with high directivity. There is sex.

  Metal moldings formed from aggregate molds contain from about 1% to about 100% finely solidified microstructures. Even a small amount of solidified microstructure is desirable for enhancing the mechanical properties of the molded article. This is because, as shown in the present invention, the formation of a small amount of fine solidification microstructure prevents defects such as porosity that causes shrinkage due to directional solidification and optimal raw material inflow.

  Molded articles according to the present invention containing finely solidified microstructure regions can be formed from any solid solution alloy that solidifies in a dendritic manner. These include both ferrous and non-ferrous materials. The dendrite arm spacing in both the coarse and fine solidified microstructure regions varies depending on the metal used. For aluminum alloys, the coarsely solidified microstructure region typically has a dendrite arm spacing greater than about 50 micrometers. In some embodiments, the coarse solidified microstructure has a dendrite arm spacing of about 50 to about 200 micrometers. Even in aluminum alloys, the finely solidified microstructure has a dendrite arm spacing of less than about 15 micrometers, and in some embodiments has a dendrite arm spacing of about 5 to about 15 micrometers.

Solidification occurs partly by dendritic solidification, partly by eutectic solidification, and many Al-Si alloys, preferably those shown as Al-7Si-0.4Mg (A356) alloys, are fine It shows dendritic and / or fine eutectic microstructures. The conventional cooling curve for the mixed dendrite / eutectic alloy is shown as “a-h” in FIG. Starting from the point “a” at the pouring temperature (Tp), the liquid alloy is cooled to the point “c” (the point at which dendrites (dendrites) begin to form) at the liquid temperature (TL). Dendritic (dendritic) growth is completed at point “e”, which indicates the eutectic temperature (TE). The temperature drop ceases and the stable period is reached until eutectic solidification is completed at point “g”. At this point, the part is completely frozen and further cooled to room temperature according to “gh”. The alloy of the second embodiment, which is an Al-Si alloy that can effectively benefit from the application of the present invention, is the widely used A319 alloy. The alloy contains some copper. The alloy is somewhat different from A356 in having a eutectic formation region “eg” that is not an isotherm, and the horizontal plateau region “eg” in FIG. 5 exhibits a stable downward slope. However, the same principle applies exactly.

  For example, slow conventional cooling, such as silica sand molds, results in dendritic structures with DAS in the region of 200 to 50 micrometers. The dendrites are surrounded by eutectics, which are characterized by a spacing in the region of 20 micrometers to 2 micrometers. This is shown herein as a conventional eutectic microstructure or a “coarse” eutectic microstructure (FIG. 6).

  If the alloy is totally cooled by ablation, the cooling profile is thought to follow the path “bijkl” so that the total solidified microstructure consists of fine dendrites (dendrites) and very fine eutectics. However, as noted above, the structure is not easily achieved and has not yet been tested by the inventors, but it has the potential to be achieved under special conditions. These conditions include situations where the mold is very insulated and freezing is very directional. Nevertheless, molded articles with excellent mechanical properties can be achieved without depending on these special conditions.

  In general, a more practical cooling profile is indicated by the cooling curve “abcdmno”. In this situation, cooling from “cd” produces a coarse dendrite and strengthens the weak, partially molded product that is hot and partially solidified prior to the application of the coolant. . Next, the dendrites (dendrites) and eutectic are both quenched, and the fine solidification microstructure is fine dendrites (DAS in the region of 30 to 5 micrometers) and fine It includes both eutectics (which cannot be analyzed at 1000X magnification because its width is about 1 micrometer).

  The two regions resulting in a double solidified microstructure region formed visually very different regions as analyzed from the microscope. FIG. 7 shows the structure when ablation is applied in a timely manner to freeze some dendritic material, followed by rapid freezing of all of the eutectic. The eutectic is so fine that it cannot be analyzed in this figure, but appears as a uniform light gray phase. (In this case, the alloy cannot be purified by the addition of chemical modifiers such as Na or Sr). Furthermore, because all of the eutectic freezes along the path “mn”, the entire eutectic phase exists between both coarse dendrites (dendrites) and fine dendrites (dendrites), In FIG. 7, it can be visually confirmed that the image is uniformly fine.

  Uniform and very fine eutectic is a feature common to ablated solidified microstructures, unique to ablation cooling alloys that are not affected by chemical modifiers such as Na or Sr to refine the microstructure Is. In this structure, some finely distributed impurities and associated pores can also be seen, as shown in FIG. The mechanical properties of the molded part are surprisingly insensitive to many defects of this type and size. FIG. 9 shows a similarly fine eutectic after solution heat treatment. In FIG. 9, the eutectic is somewhat coarser and the interfacial energy is reduced as is often seen in a two-phase structure that has been subjected to a high temperature treatment.

  As a general rule, although not usually desirable, freeze all dendrite (dendrites) to have a rough structure and perform only the late application of ablation cooling (eg at point “f” in FIG. 5) Is possible. In this case, some eutectics freeze in a coarse eutectic structure. Such a structure is shown in FIG. The final region of the eutectic that freezes due to the effect of ablation cooling has a very fine structure and is generally not porous, showing only a fine phase rich in iron, but this phase is generally too small In FIG. 10, it cannot be visually recognized. At higher magnification, some iron-rich phase can be seen as shown in FIG.

  For mixed dendrites / eutectic alloys, many of the benefits of ablation can be enjoyed, resulting in the structures seen in FIGS. 10 and 11, which gradually increase the residual liquid. This is because solidification is effective in giving directivity to the molded product. The alloy shown in FIG. 10 is, for example, heat-treated, and therefore, all of the eutectic phase silicon particles are roughened to some extent.

  In practice, however, it is desirable and can be easily achieved that some coarse dendritic structures are formed prior to performing ablation (starting point “d” in FIG. 5). Thus, the usual resulting dendritic microstructure is double as described above and contains relatively uniformly fine eutectics.

  As before, if the application of the coolant is very slow, for example following the path “gq” in FIG. 5, of course, the molded part will solidify completely before the coolant is applied. The implementation of ablation cannot affect the solidification microstructure of the molded article. Such cooling of the molded article is not included in the present invention and is within the scope of casting production methods known to those skilled in the art.

  In conventional cooled molded articles (where “h” or “q” is the end point of the cooling path), the final region of the solidified molded article is often porous. In addition, such molded articles often include a thin plate of beta iron deposits that, when made of a typical aluminum alloy such as A356 alloy, further impairs properties.

  Ablation-cooled moldings (including both dendritic moldings and dendritic moldings / eutectic moldings) with fine solidification microstructures can be found in moldings molded by conventional casting methods Generally does not have many defects. In one embodiment, a molded article having a finely solidified microstructure portion is substantially non-porous. The rapid freezing and directivity obtained with ablation reduces both gas and shrinkage porosity. In other embodiments, a molded article having a finely solidified microstructure portion does not have a harmful iron-rich platelet that is substantially rich in iron. In yet another embodiment, the molded article is substantially free of both porosity and harmful plates that are rich in iron. Without being bound by any particular theory, the size reduction of the iron-rich plate is a result of more rapid cooling (quenching) of the liquid alloy. The reduction in porosity is also due to this cooling rate. In addition, by allowing the ablation to act gradually and gradually, the cooling action of the water (or other fluid) will be stable along the length of the molded part and will be highly directional toward the source of the supply metal. Causes form coagulation. Furthermore, maintaining such a relatively narrow paste-like region due to such a high temperature gradient increases the efficiency of promoting the raw material supply of the molded product.

  The substantial reduction or removal of porosity that causes shrinkage is important and will be described again below. The porosity causing shrinkage is normally expected to occur in a region of a molded product such as a hot spot to which no raw metal is supplied. However, in principle, when the freezing process is directed, the source metal can be supplied to the region. Water or other cooling fluid is applied to ablate and cool the mold and systematically cause solidification during the casting process, creating a characteristic strong directional temperature gradient. In this way, if the effect of the present invention is applied correctly, the source metal is supplied until those areas isolated from the feed liquid in conventional molded products are easily and automatically strengthened. Or obtain greatly improved robustness.

  For this reason, alloys that cannot normally be cast as shaped moldings (molded castings) (for example, those due to high temperature brittleness such as wrought alloys 6061 and 7075, or alloys with a long freezing range such as alloys 7075 and 852) The alloy ablation technique can be easily and beneficially cast into a predetermined shape. In addition, the ablated molded article is characterized by a unique, immediately identifiable solidification microstructure.

The metal molded product of the present invention having a fine solidified microstructure region and formed from an aggregate mold will be further described in detail in the following examples. The examples only illustrate potential embodiments of formed metal moldings with finely solidified microstructure regions, and do not limit embodiments of the present invention.
(Example)
In one example applying the technology of the present invention, a single specimen was cast using a mold having a diameter of 20 mm and a length of 200 mm and having a small conical reservoir filled at one end and acting as a feeder. . The mold material was silica sand bonded with a water soluble inorganic binder as described in co-pending US patent application Ser. No. 10 / 614,601.

  A thermocouple was inserted into the cavity of the mold and placed at the base of the feeder and the base of the cavity. Two additional thermocouples were equally spaced along the axis. These four thermocouples were labeled TC1 (presser), TC2 (upper center), TC3 (lower center) and TC4 (bottom).

  Aluminum alloy 6061 at 730 ° C. (1350 ° F.) was injected into the cavity with the axis in the vertical direction. Next, within about 10 seconds, water at 20 ° C. (68 ° F.) was poured from a nozzle directed to the base of the mold and ablation of the mold was started to proceed upward from the base. The traveling speed upward from the ablation surface was about 25 mm / s.

  The cooling trajectories of the four thermocouples were recorded as shown in FIG. Thermocouple TC4 appeared to cool rapidly, showing freezing and cooling to below the boiling point of water in just about 2 seconds. At this point, the thermocouple TC3, located immediately above, was recorded that the metal was still molten and cooling had just begun. The pattern was repeated until reaching the mold continuously. (A sudden change in temperature of TC2 recorded an unintentional instantaneous loss of cooling water in this experiment). The thermal trajectory confirms that the temperature gradient caused by the application of ablation was sufficient to freeze and cool the melt to near ambient temperature within a distance shorter than the distance between thermocouples (50mm) did. Furthermore, the effect could be easily and accurately maintained for the average length of the molded article of an automobile.

  In the second example, a knuckle molded article for an automobile was made of alloy A356. Many knuckle moldings are said to be difficult to cast because they are complex and the heavy parts are isolated from the location where the feeder is added. The molded product was no exception. The molded product was filled with metal at 750 ° C (1385 ° F) at an inclined feeding position, but it took 8 seconds to fill, and an excellent surface finish was obtained. The feeder (presser) was positioned at the far end of the molded product from the injection cup and the lower vertical gate. The vertical gate and feeder thermocouple are shown in FIG. Freezing occurred at the vertical gate and the first ablation was achieved in about 20 seconds. Next, freezing proceeded across the mold and was triggered to arrive at the feeder after about 90 seconds, which is where the feeder was frozen at a similar time of only about 20 seconds. there were.

Three banks of water spray nozzles were used at a water pressure of about 0.7 bar (about 10 psi) and a temperature of about 40 ° C. (about 100 ° F.) to achieve ablation of the molded article.
It was found that the molded product was completely strong and had properties that exceeded specifications.

  In the third example, a control arm molded article (automobile steering / suspension part) was cast in the mold material described in Example 1. An A356 alloy having an approximate composition of Al-7Si-0.35Mg-0.2Fe at about 700 ° C. (about 1400 ° F.) was fed into the mold. Solution heat treatment is performed at 538 ° C (1000 ° F) for 0.5 hours, water is quenched at 26 ° C (78 ° F), and ripening is performed at 182 ° C (360 ° F) for 2.5 hours. ) Four specimens were cut from three moldings numbered 45, 46 and 47, respectively. A molded product (cast product) obtained by ablation cooling of this mold was cut and processed to produce a tensile test piece, which was subjected to T6 heat treatment. The test piece was subjected to a tension test, and the result is shown in FIG. 14 together with the average value. (There is one elongation value as low as 9%, but in this case, it has been found that the quality control of the melt was not optimal and seems to have been mixed with a large amount of oxide). The results are shown in FIG. 15 in comparison with competing casting methods. This property exceeds all current competing best methods and is clearly attractive.

When using the ablation casting method, it is possible that certain process conditions result in a conventional microstructure from the ablated mold. As an example, 852 aluminum alloy (Al-6Sn-2Cu-1Ni-0.75Mg alloy) is known as an alloy that freezes over a long range, and its eutectic freezes at a melting point of approximately tin (232C, 610F). The alloy was ablated by using an ablation casting process. The mold was symmetrical, and the same mold was divided into two and produced from a single-sided pattern. The metal was injected at or near 700C (1275F). The thickness of the molded piece was about 75 mm (3 inches) in diameter. The mold is injected by gravity 10
Achieved in seconds. It was allowed to stand for about 180 seconds, and most of it solidified and reached the alpha phase. After a standard solidification rate controlled by the mold aggregate (in this case, silica sand), the mold was ablated.

  Ablation conditions are described below. The water pressure used for ablation is about 1 bar (15 psi). The amount of application was limited by a spray nozzle. However, the amount of water is of little importance since the pressure controls the influence of water on the mold surface. The procedure was the same as before, but a constant cooling rate was obtained and the same characteristics as when produced with a metal mold were obtained. (That is, the permanent mold of FIG. 16). In this regard, FIG. 16 shows the relationship between the various casting methods and the cell size and solidification rate of dendrites (dendrites) for aluminum alloys. A conventional permanent mold microstructure is shown in FIG. 17a. FIGS. 17b and c are the same alloy but were made using this ablation method. The same magnification (100X) was used in all three figures of Figures 17a-c. The final eutectic structure was much closer to that produced by a permanent mold. Such conventional microstructures can be achieved by ablation methods, but in some conditions, the microstructures are unique to ablation and are due to a very fine phase (possibly due to dendrites). Microstructures, including but more often due to very fine eutectics, can be observed.

  In order to obtain conventional microstructures (such as those made from permanent molds) using the ablation method, several variables can be important. An important parameter is the mold aggregate itself. Furthermore, it goes without saying that the volume, pressure and temperature of the cooling medium used to remove the mold while simultaneously causing solidification of the metal. While propelling along the length of the molded article, the residence time of the cooling spray impinging on the mold can be beneficially adjusted while taking into account the local surface to volume ratio (geometric factor). The dissolution rate of the mold adhesive can be reduced, thereby slowing the ablation rate of the mold and decreasing the heat extraction rate. This can limit the speed to produce a conventional microstructure. Furthermore, the water pressure can be changed. Initially, higher pressures can be used to remove the mold aggregate. The pressure can then be reduced so that the same cooling rate as with conventional metal casting methods can be obtained.

  Conventional microstructures can be achieved in this way, but have the benefit of being added significantly by the ablation method, which makes the ablation method uniquely desirable. First, since the final solidification occurs with sufficient liquid in front of the final solidification tip that can fully adapt to thermal tension, it is easy to control the residual stress in the molded article. Secondly, the porosity of the molded product is considerably reduced (in fact, in most cases to zero) due to the excellent directional solidification. This occurs as a result of the high applied temperature gradient and can only be achieved by ablation.

  As a fourth example, an automobile suspension control arm molded product was cast with the material described in Example 1. A B206 alloy having an approximate composition of Al-4.8Cu-0.4Mn-0.28Mg-0.07Fe was injected into the mold at about 1265F in the range of plus or minus 15F. The ablation cooling of these molds was then subjected to T4 and T7 heat treatments. The picture of the relevant part is the frame of FIG. 18, in which the position where the tension sample was next machined is shown. The tensile properties obtained from this part are shown in FIG. 19 and compared with standard tabular values obtained from individual cast specimen data from the published literature on this type of alloy shown in FIG. A photomicrograph taken from the center of a portion of the thick profile prior to heat treatment is shown in FIG. The characteristics were again similar; apparently attractive, approximately equal to the characteristics produced from individually cast permanent mold specimens, exceeding the characteristics of all other casting media listed . These values are particularly attractive in that they were obtained from the region with a piece thickness of more than 2 inches. Under conventional sand and permanent mold methods, one of ordinary skill in the art would be listed as individual cast specimen data in FIG. 20 (based on a 1/2 inch thickness gauge diameter piece with an as-cast surface). One would think that the ductility from a piece machined from a larger piece would reach a much lower value. These comparisons also show that the manufacture of one of the sizes and geometries shown in Figure 18 can be achieved in all AA 2XX series alloys, due to the uniqueness of the heat treatment in the casting / alloy combination. It should be noted that it does not take into account the fact that it is a rigorous engineering challenge to use permanent molds due to the increasing tendency. Such would in fact be physically impossible without means that would make the resulting parts prohibitively expensive.

  The micrograph in FIG. 21 shows the double microstructure described above as seen by solidification by ablation. A coarse DAS with an average value of 43um and a maximum value of 85um is the host (major part), and finer DAS with an average order of 22um is present in a patch. The mechanical properties described in FIG. 17 show the characteristics expected from fine DAS. The intermetallic compound visible in FIG. 19 is primarily copper aluminide, which dissolves during the applied solution heat treatment as a subsequent tempered portion of both T4 and T7. . Those skilled in the art of producing 200 series aluminum moldings will recognize that the fine structure is advantageous with regard to the economics of heat treatment. The three-step solution treatment required to dissolve the copper aluminide mentioned above for thick sand molds is eliminated, and it is generally applied to thin and / or rapidly solidified molds. Stage processing would be advantageous.

  Molded articles cast or molded using aggregates and having a solidified microstructure have been described with respect to the present invention and various exemplary embodiments have been described. Those skilled in the art will recognize variations and modifications, and it will be understood that the invention and the claims encompass such variations. The development of the invention is intended to cover all such modifications and alternatives as long as they fall within the scope of the appended claims and the like.

Claims (8)

A metal molded product formed from an alloy containing aluminum by a rapid cooling process in a mold containing aggregate and showing a molded microstructure, wherein the microstructure is a first region located in the vicinity of the surface of the metal molded product, A first region having a coarse solidified microstructure and a second region located inside the first region, the second region having a fine solidified microstructure,
The first region includes dendrites having dendrite arms spaced at intervals of 20 to 200 micrometers;
The molded metal molded product , wherein the second region includes a dendrite having dendrite arms separated by an interval of 5 micrometers to 15 micrometers . The shaped metal molded article according to claim 1, wherein the first region has a 100% coarse solidification microstructure and the second region has a 100% fine solidification microstructure . A third region located between the first region and the second region, the third region including a double solidified microstructure region, wherein the double solidified microstructure region is (i) 1 The shaped metal molded article according to claim 2, comprising the coarse solidified microstructure part and (ii) one or more finely solidified microstructure parts . One or more coarsely solidified microstructure portions of the double solidified microstructure region include dendrites having dendrite arms spaced apart by 20 to 200 micrometers, wherein one or more of the double solidified microstructure region 4. The shaped metal molded article according to claim 3, wherein the finely solidified microstructure part includes a dendrite having dendrite arms separated by an interval of 15 micrometers or less . The shaped metal molded article according to claim 4, wherein the second region is continuous from a bottom portion, which is a distal end of the molded article, to a feeder, which is a proximal end . The finely solidified microstructured portion of the second region is finer than a similar metal having a similar mass or cross-sectional thickness produced by a casting method involving conventional aggregates. of shaped metal casting. The shaped metal molded article according to claim 1, wherein the molded article is free of at least one of (i) porosity causing shrinkage and (ii) a harmful plate-like body containing a large amount of iron . The shaped metal molded article according to claim 1, wherein the first region has a dendrite arm interval of 50 micrometers to 200 micrometers .