JP2008503651A - Die-cast magnesium alloy - Google Patents

Abstract

  Magnesium-based alloys contain zinc, aluminum, calcium and / or beryllium, possibly manganese, and the remainder, except for accidental impurities, magnesium. The zinc and aluminum content falls within the quadrilateral defined by the straight lines AB, BC, CD, and DA, and the calcium and beryllium content is the quadrilateral defined by the straight lines EF, FG, GH, and HE. Entering the range, where A is 10% Zn-2.5% Al, B is 10% Zn-5% Al, and C is 13% Zn-6.4% Al; D is 19% Zn-2.5% Al, E is 0.01% Ca-0% Be, F is 1% Ca-0% Be, and G is 0% Ca- 0.0025% Be and H is 0% Ca-0.0001% Be.

Description

  The present invention relates to magnesium / zinc / aluminum (Mg—Zn—Al) alloys containing small amounts of calcium and / or beryllium.

Due to their superior strength to weight ratio, magnesium alloys are well recognized as commercially attractive materials. The most commonly used magnesium alloy is AZ91 which contains about 90% magnesium, 9% aluminum and 1% zinc. On a weight basis, zinc is about 65% of the price of magnesium, so magnesium alloys with high zinc content are desirable if they exhibit commercially satisfactory properties.
A serious disadvantage of using magnesium alloys is the risk of ignition of the molten alloy. A magnesium alloy that is sufficiently resistant to oxidation and avoids the need for a protective cover gas or the like when the molten alloy is exposed to air is advantageous.

Patent Document 1 issued in 1945 relates to a magnesium-based alloy and a method for preventing the oxidation of magnesium and magnesium-based alloy. The patent states that:
“Its general purpose is to provide an improvement that alleviates the problems arising from the oxidizing nature of magnesium when in contact with air, water vapor or other media containing oxygen. The usefulness is not only due to its essential properties, or the properties that can be imparted to it by alloying it with a small amount of other metals, but by remelting, casting, Depending on ease of use or otherwise ease of shaping into various conditions and shapes required for final use Magnesium is prone to catastrophic oxidation in the molten state Under many conditions that are normal for handling other molten metals, the molten magnesium burns or otherwise reverts back to an oxide. When in the solid state, magnesium-based alloys oxidize to relatively severe limits under certain conditions, and extensive operations in the molten state of magnesium and magnesium-based alloys are planned to mold or use the metal. The problem given by this remarkable oxidation tendency is almost always encountered and is common in the magnesium industry because it is the preparatory step necessary for the new work. "

  “In the face of these problems, the industry has devised methods and apparatus that protect molten magnesium and magnesium-based alloys from contact with air and water vapor or other harmful media during manufacturing operations. One is to wrap the molten metal in a protective gas, the other is to always protect the exposed surface with salt flux, and other more complex methods and equipment are often needed. Other means have also been explored to minimize the tendency for oxidation of magnesium and magnesium-based alloys and thus reduce the need for the above-mentioned expensive protection measures. Magnesium and magnesium-based alloys so alloyed with magnesium have been previously Although it does not oxidize vigorously, the overall effect is not sufficient and only supplements the usual protective measures: better results have been obtained when beryllium is added to magnesium or magnesium-based alloys, It has been found that the effect of beryllium to minimize magnesium oxidation is much greater than that of the corresponding amount of calcium. "

Patent Document 2 states that “the amount of beryllium was increased to prevent combustion as the oxygen content of the atmosphere increased”, Mg—Al—Zn—Si containing 0.0025 to 0.0125% dissolved beryllium. -It relates to a Mn alloy. US Pat. No. 4,543,234 also states that “a beryllium content of about 0.001 percent is considered insufficient for the purpose of preventing excessive oxidation of molten magnesium”.
The title “Characterization of the oxidation surface layer on non-combustible” by M. Sakamoto, S. Akiyama, and K. Ogi announced at the 4th Asian Foundry Congress, October 27-31, 1996. The paper “Ca-bearing Mg melts” reported the ignition temperature of calcium-containing magnesium-based alloys (see FIG. 2 of that paper). The measured ignition temperature varied considerably between repetitions of the same alloy composition. In most of these iterations, alloys of more than 0.5% calcium did not ignite until the melting point of the alloy was exceeded. However, there are also examples in which ignition occurs below the melting point for calcium levels as high as 4%.

  Patent Document 3 relates to a magnesium alloy having excellent high-temperature characteristics and not related to oxidation inhibition. U.S. Patent No. 6,057,059 is known to add calcium to improve high temperature strength and creep resistance, and note that a calcium content of 0.2 wt% or more is desirable. It further notes that the addition of calcium significantly reduces the castability and makes it impossible to cast the alloy by conventional die casting methods. U.S. Patent No. 6,057,059 teaches that the castability of a magnesium-aluminum-calcium alloy can be restored by including zinc. A zinc content of about 6 to about 12% by weight, more preferably about 6 to about 10% by weight is taught, “the upper limit of the zinc range is about 12% by weight, more so that the alloy density remains low. Preferably it is set to about 10% by weight. " Due to the presence of zinc, calcium is "added up to 2% by weight, preferably up to 1.5% in order for the alloy to obtain maximum creep resistance and at the same time maintain good castability" It is described that it becomes possible.

Patent document 3 illustrated the alloy described below. Therefore, Patent Document 3 does not exemplify an alloy containing Zn exceeding 8.15%.
Mg-5% Al-8% Zn, Ca content in the range between 0 and 2% (see FIG. 2 and FIG. 3 of Patent Document 3)
Mg-5% Al-1% Zn, Ca content between 0 and 2% (see FIG. 2 and FIG. 3 of Patent Document 3)
Mg-4.57% Al-8.15% Zn-0.23% Ca-0.25% Mn (see Table 1 of Patent Document 3)
Mg-4.74% Al-8.12% Zn-0.59% Ca-0.25% Mn (see Table 1 of Patent Document 3)
Mg-4.67% Al-8.12% Zn-1.17% Ca-0.27% Mn (see Table 1 of Patent Document 3)
U.S. Pat. No. 2,380,200 U.S. Pat. No. 4,543,234 US Pat. No. 5,855,697

The present invention
A is 10% Zn-2.5% Al,
B is 10% Zn-5% Al,
C is 13% Zn-6.4% Al;
Amounts of zinc (Zn) and aluminum (Al) that fall within the quadrilateral defined by the straight lines AB, BC, CD, and DA where D is 19% Zn-2.5% Al;
E is 0.01% Ca-0% Be;
F is 1% Ca-0% Be,
G is 0% Ca-0.0025% Be,
An amount of calcium (Ca) and / or beryllium (Be) that falls within the quadrilateral defined by the straight lines EF, FG, GH, and HE, where H is 0% Ca-0.0001% Be;
Optionally with manganese;
An alloy is provided, the remainder of which consists of magnesium, excluding incidental impurities. Unless otherwise specified, percentages in this document are weight percent.

  The quadrilateral defined by the straight lines AB, BC, CD, and DA is shown in FIG. 1, which is the aluminum to zinc content compartment. The quadrilateral defined by the straight lines EF, FG, GH, and HE is shown in FIG. 2, which is the beryllium to calcium content compartment.

  All of the alloys of the present invention are at least 10% zinc, preferably more than 11% zinc, more preferably more than 12% zinc, more preferably about 12-14% zinc, most preferably about 12-13%. Containing zinc. Most surprisingly, the present inventor has found that the addition of the zinc can suppress the ignition of the molten alloy even in the absence of an alkaline earth element such as beryllium or calcium. While not wishing to be bound by theory, it is believed that this suppression of ignition is a result of the vapor pressure of magnesium and zinc and the amount of zinc present in the alloy.

  The vapor pressures of zinc and magnesium on the molten alloy are described in `` Vapor Composition and Activities in Mg-zn Liquid Alloy at 923K '' by KT Jacob, S. Srikanth and Y. Waseda in Thermochimica Acta, 1988, vol 130, pages 193-203. It can be calculated using information from a paper with the title " The ratio of zinc vapor pressure to magnesium vapor pressure increases rapidly as the amount of zinc in the molten alloy increases. A molten alloy containing 10 wt% zinc and 90 wt% magnesium is calculated to produce steam containing 22 wt% zinc and 78 wt% magnesium. While not wishing to be bound by theory, it is believed that zinc vapor prevents the ignition of magnesium vapor.

  Although molten alloys containing more than 10% zinc resist ignition, they tend to form a dark layer on the surface of the solidified sample. It has been found that the addition of small amounts of calcium and / or small amounts of beryllium is sufficient to provide a glossy surface appearance when solidified. In order to produce this effect, it has been found that as little as 0.01% calcium or as little as 0.0001% beryllium in combination with the zinc and aluminum content according to the invention is sufficient. Without wishing to be bound by theory, it is believed that the glossy surface appearance is a result of the concentration of calcium and / or beryllium content of the oxide film formed on the surface of the melt.

  When present, the calcium content is preferably 0.01-0.5%, more preferably 0.01-0.3%, more preferably 0.02-0.3%, more preferably 0.05-0.3%. It is 0.3%, more preferably 0.05 to 0.2%, more preferably 0.05 to 0.15%, and most preferably about 0.1%. Calcium contents above 1% are undesirable because they have been found to impair the mechanical properties of the alloy and cause die soldering when die cast.

  When present, the beryllium content is preferably 0.0002-0.0025%, more preferably 0.0002-0.002%, more preferably 0.0005-0.002%, more preferably 0.0005. 0.0015%, more preferably 0.0005 to 0.001%, and most preferably about 0.0008%. A beryllium content above 0.0025% is not necessary to obtain the desired effect. In view of the toxicity of beryllium, it is therefore desirable to minimize its use by keeping the beryllium content below this level.

Manganese (Mn) is an optional component of the alloy and can be included when iron (Fe) needs to be removed. When Mn is one component, it is preferably less than 1%, more preferably less than 0.75%, more preferably 0.1-0.5%, more preferably 0.2-0.4%, most Preferably it is present in an amount of about 0.3%. Other elements can also form optional components of the alloy if they do not adversely affect the commercially important properties of the alloy.
The presence of iron reduces the corrosion resistance. The iron contained in the alloy of the present invention is preferably less than 100 ppm, more preferably less than 40 ppm, and most preferably substantially free of iron.

The inventor has found that the corrosion resistance decreases as the aluminum content decreases. All alloys of the present invention contain a minimum of 2.5% aluminum. The alloys of the present invention preferably contain 2.5-5% aluminum, more preferably about 3-4.5% aluminum, most preferably about 3.5-4% aluminum.
The present inventor has also found that the brittleness increases toward the straight CD side with a lot of aluminum and a lot of zinc.

The presence of nickel (Ni) reduces the corrosion resistance. The nickel contained in the alloy of the present invention is preferably less than 25 ppm, more preferably less than 10 ppm, and most preferably substantially free of nickel.
The presence of silicon (Si) reduces corrosion resistance and mechanical properties. The silicon contained in the alloy of the present invention is preferably less than 0.1%, more preferably less than 0.08%, and most preferably substantially free of silicon.

In addition to resistance to ignition when melted, the various preferred embodiments of the present invention include one such as recyclability, castability, resistance to hot cracking, corrosion resistance, creep resistance, low sound deadening rate and good surface finish. Or exhibit several other commercially desirable properties.
A significant commercial hindrance to the use of magnesium alloys is waste resulting from difficulties in recycling so-called “return materials” including runners, biscuits, etc. from die casting. Generally, 30-70% of die casting consists of runners and biscuits that need to be recycled. Problems in recycling magnesium alloys are generally attributed to the high amount of surface oxides that result in high melt loss in scale and sludge form. In general, recycling is done in a separate operation to allow the removal of oxides without having to mix them into the melt and include them in subsequent die casting. Surprisingly, the inventors have determined that at least preferred embodiments of the alloys of the present invention have enhanced recyclability. The runners and other die-casting debris of the alloy of the present invention were successfully returned directly to the melt without the need for any purification or purification. While not wishing to be bound by theory, it is believed that this recyclability is closely related to the improvement in oxidation behavior that causes suppression of ignition of the molten alloy.

Without addition of beryllium, magnesium alloys containing varying amounts of aluminum, zinc and calcium were melted at 700 ° C. in a protective atmosphere containing sulfur hexafluoride (SF ₆ ) and then poured into molds in air. The upper surface of the resulting casting was left exposed to air. Four different types of behavior were observed depending on the composition.
Behavior 1—The casting surface first turned black and then ignited as shown in FIG.
Behavior 2—The surface turned black, but did not ignite as shown in FIG.

Behavior 3—The surface was initially shiny and then ignited as shown in FIG.
Behavior 4—The surface retained gloss without ignition as shown in FIG.
Table 1 is a list of behaviors observed for a series of different alloys. Addition of more than 10% zinc was sufficient to prevent combustion and resulted in a blackened surface. Addition of calcium without zinc resulted in a glossy surface but required 0.8% calcium to prevent ignition. The addition of calcium to an alloy containing enough zinc to prevent burning resulted in a partially shiny surface with only 0.05% calcium, converting the surface to a shiny appearance. An increase in calcium content results in a continuous decrease in blackening. No blackening was observed at 0.4% calcium.

  Alloys containing 10% zinc (see Table 1) turned black and ignited shortly, while alloys with higher zinc content did not ignite. The alloy was deliberately poured at a high temperature (700 ° C.) to remove the low temperature, which is the dominant reason not to ignite. Commercial casting is approximately 30-40 ° C. below this, and naturally the tendency to ignition is expected to decrease.

A further melt was prepared and poured into the mold as in Example 1 above. A metal scraper was applied to the metal surface shortly after casting but while the metal was still melting.
FIG. 7 shows the behavior of pure magnesium that was oxidized so quickly that it was impossible to expose the bright metal.
FIG. 8 shows the behavior of an alloy of Mg-5% Zn that is also rapidly oxidized. The glossy metal could be exposed, although it was only a small fraction of a second.

FIG. 9 shows the behavior of the Mg-10% alloy. The tendency to oxidize was greatly reduced as indicated by the absence of “cauliflower-like” growth surrounding and an increase in exposed bright metal.
FIGS. 10 and 11 show the behavior of alloys of Mg-15% Zn and Mg-20% Zn, respectively. In either case, it was relatively easy to expose the bright metal, which took several seconds to oxidize again. Neither formed “cauliflower-like” growth.

A further series of alloys were produced, all containing 0.1% calcium and varying amounts of zinc. FIGS. 12, 13 and 14 show the appearance of the alloy immediately after casting (FIGS. 12a, 13a and 14a) and after a short time (about 1 minute) (FIGS. 12b, 13b and 14b). Is shown.
Figures 12a and 12b show the behavior of the zinc-free alloy. After initially appearing shiny, the alloy developed “cauliflower-like” growth and then ignited.

Figures 13a and 13b show the behavior of zinc containing 5% zinc. This alloy also developed a “cauliflower-like” growth and ignited, but at a slower rate than the zinc-free alloy of FIG.
Figures 14a and 14b show the behavior of an alloy of 10% zinc. In this alloy, both “cauliflower-like” growth and ignition were suppressed. The final appearance after leaving the sample air cooled to room temperature did not change from FIG. 14b.

  A further melt was prepared and poured into the mold as in Example 1 above. The melt contained 13% zinc, 3.6% aluminum and varying amounts of beryllium and calcium. The calcium and beryllium contents of these alloys are shown in Table 2. Alloys 1 and 6 were free of calcium and Alloys 1-4 were free of beryllium. The final appearance of the casting is shown in FIG. All alloys containing some calcium or beryllium solidified with a shiny skin. Alloy 1 containing neither calcium nor beryllium solidified with a blackened skin.

  Prior art publications are referenced herein, but this reference forms part of the fact that these documents are commonly known in the art in Australia or any other country. It should be clearly understood that it is not of a nature to admit.

It is a graph which shows the content division of aluminum with zinc. It is a graph which shows the content division of beryllium versus calcium. It is a figure which shows the behavior 1 in the surface of a casting. It is a figure which shows the behavior 2 in the surface of a casting. It is a figure which shows the behavior 3 in the surface of a casting. It is a figure which shows the behavior 4 in the surface of a casting. FIG. 4 is a diagram showing the behavior of pure magnesium that was oxidized very quickly and was unable to expose the bright metal. It is a figure which shows the behavior of the alloy of Mg-5% Zn which is rapidly oxidized. It is a figure which shows the behavior of a Mg-10% alloy. It is a figure which shows the behavior of Mg-15% Zn alloy. It is a figure which shows the behavior of the alloy of Mg-20% Zn. It is a figure which shows the behavior of a zinc-free alloy. It is a figure which shows the behavior of zinc containing 5% of zinc. It is a figure which shows the behavior of a 10% zinc alloy. It is a figure which shows the final external appearance of a casting.

Claims (16)

A is 10% Zn-2.5% Al,
B is 10% Zn-5% Al,
C is 13% Zn-6.4% Al;
Amounts of zinc (Zn) and aluminum (Al) that fall within the quadrilateral defined by the straight lines AB, BC, CD, and DA where D is 19% Zn-2.5% Al;
E is 0.01% Ca-0% Be;
F is 1% Ca-0% Be,
G is 0% Ca-0.0025% Be,
With an amount of calcium (Ca) and / or beryllium (Be) that falls within the quadrilateral defined by the straight lines EF, FG, GH, and HE, where H is 0% Ca-0.0001% Be;
Optionally with manganese;
An alloy characterized in that the remainder consists of magnesium, excluding incidental impurities.   The alloy according to claim 1, characterized in that it contains more than 11% zinc.   3. An alloy according to claim 2, characterized in that it contains 12% to 14% zinc.   4. An alloy according to any one of claims 1 to 3, characterized in that it contains 2.5% to 5% aluminum.   5. Alloy according to claim 4, characterized in that it contains 3% to 4.5% aluminum.   The alloy according to any one of claims 1 to 5, characterized in that it contains 0.01% to 0.5% calcium.   7. An alloy according to claim 6 containing 0.05% to 0.2% calcium.   The alloy according to any one of claims 1 to 7, characterized in that it contains 0.0002% to 0.002% beryllium.   9. Alloy according to claim 8, characterized in that it contains 0.0005% to 0.001% beryllium.   10. An alloy according to any one of the preceding claims, containing manganese in an amount of less than 1%.   11. Alloy according to claim 10, characterized in that it contains 0.1% to 0.5% manganese. 11% to 13.5% zinc,
3% to 4.5% aluminum,
0.05% to 0.15% calcium;
0.0005% to 0.001% beryllium;
In some cases, less than 0.5% manganese and
Magnesium-based alloy characterized in that the remainder consists of magnesium, excluding incidental impurities. 11.5% to 13.5% zinc;
3% to 4.5% aluminum,
In some cases, less than 0.5% manganese and
Either 0.05% to 0.15% calcium or 0.0005% to 0.001% beryllium;
Magnesium-based alloy characterized in that the remainder consists of magnesium, excluding incidental impurities. 11.5% to 13.5% zinc;
3% to 4.5% aluminum,
0.2% to 0.4% manganese,
0.05% to 0.15% calcium;
0.0005% to 0.001% beryllium;
Magnesium-based alloy characterized in that the remainder consists of magnesium, excluding incidental impurities. 11.5% to 13.5% zinc;
3% to 4.5% aluminum,
0.2% to 0.4% manganese,
Either 0.05% to 0.15% calcium or 0.0005% to 0.001% beryllium;
Magnesium-based alloy characterized in that the remainder consists of magnesium, excluding incidental impurities.   16. 12% to 13% zinc, 3.5% to 4% aluminum, less than 0.08% silicon, less than 40 ppm iron, and less than 10 ppm nickel. The alloy as described in any one of them.

Images