CN109338171B - A kind of Zn-containing cast aluminum-magnesium-lithium alloy and heat treatment method thereof - Google Patents

Abstract

The invention discloses a Zn-containing cast aluminum-magnesium-lithium alloy and a heat treatment method thereof; the aluminum-magnesium-lithium alloy comprises the following components: 2.1-2.5wt% Mg, 3.1-3.5wt% Li, 0.1-1.0wt% Zn , the total amount of impurity elements is less than 0.15wt%, and the balance is Al. The present invention also relates to the heat treatment method of the aforementioned Zn-containing cast aluminum-magnesium-lithium alloy, including two processes of three-stage solution treatment and single-stage aging treatment, wherein the three-stage solution treatment process is: solution treatment at 430-440°C for 20 ~30h, then solution treatment at 500~510°C for 10~20h, and finally solution treatment at 560~570°C for 20~30h. The single-stage aging treatment process is heat preservation at 175-200°C for 8-128 hours. The invention has simple process and low cost, and the prepared cast aluminum-magnesium-lithium alloy can be applied to the fields of automobile, aerospace, military industry and the like.

Description

A kind of Zn-containing cast aluminum-magnesium-lithium alloy and heat treatment method thereof

technical field

The invention relates to the field of metal materials and metallurgy, in particular to a Zn-containing cast aluminum-magnesium-lithium alloy and a heat treatment method thereof.

Background technique

With the continuous enhancement of energy and environmental awareness, the human demand for lightweight structural materials is becoming more and more urgent. Aluminum-lithium alloy has the advantages of low density, high specific strength and specific stiffness, and is a structural material with broad application prospects in automotive, aerospace, military and other fields.

Plastic deformation can give aluminum-lithium alloys higher strength, so most of the current commercial grades of aluminum-lithium alloys are deformed alloys. American Magnesium Aluminum Company discloses an improved aluminum-magnesium-lithium alloy and its production method (publication number: CN105143492), the alloy is composed of the following components: 2-3.9wt% Mg, 0.1-1.8wt% Li, up to 1.5wt% % Cu, up to 2wt% Zn, up to 1wt% Ag, up to 1.5wt% Mn, up to 0.5wt% Si, up to 0.35wt% Fe, and some minor elements, the balance being Al. The above alloy is a deformed aluminum-magnesium-lithium alloy. In order to avoid abnormal migration of crack propagation, the addition amount of Li element is usually not higher than 1.8wt%, so as to reduce the content of Al ₃ Li phase and reduce the degree of plane slip. In addition, in the deformed aluminum-magnesium-lithium alloy, due to the low content of Li element, there are few intergranular compounds formed, and the heat treatment temperature is usually low, such as the deformed aluminum-magnesium-lithium alloy disclosed by the French Kenlian Aluminum Industry (publication number: CN103687971 ), the solid solution temperature is 300-430°C, and the aging temperature is 150°C. However, for cast aluminum-magnesium-lithium alloys with high Li content, the solid solution temperature is too low, and a large number of primary phases enriched on the grain boundaries cannot fully Solid solution into the matrix leads to poor plasticity and toughness of the alloy. At the same time, the aging temperature is too low, and the aging strengthening effect is poor.

At present, deformed aluminum-lithium alloys have been widely used in many fields, but some structural parts with complex shapes, such as turbine engine impellers and motor pistons, need to be produced by casting. Therefore, researches on casting aluminum-lithium alloys have been carried out successively at home and abroad. Cast aluminum-lithium alloys can be divided into cast aluminum-copper-lithium alloys and cast aluminum-magnesium-lithium alloys according to the alloy composition. Shanghai Jiaotong University discloses a light-weight high-strength cast aluminum-lithium alloy and its preparation method (public number: CN105648283). It consists of the following components: 3-3.5wt% Li, 1-2wt% Cu, 0.5-2wt% Mg, 0.4-0.8wt% Ag, 0.14-0.2wt% Zr, 0.3-0.8wt% Mn, the total amount of impurity elements is less than 0.25wt%, the balance is Al. This alloy belongs to the category of cast aluminum-copper-lithium alloy. Adding Cu element to Al alloy can promote the precipitation of θ′ phase, T ₁ phase and S phase during the aging process, so the alloy has high strength, but at the same time the Cu element The presence of Al also results in alloys with poorer corrosion resistance and higher density. On the basis of the previous work, the research group obtained a Zn-containing cast aluminum-magnesium-lithium alloy with better corrosion resistance and lower density by optimizing the alloy composition and heat treatment method, which is conducive to promoting the development of cast aluminum-lithium alloys Applications are important.

Contents of the invention

Aiming at the defects in the prior art, the object of the present invention is to provide a Zn-containing cast aluminum-magnesium-lithium alloy and a heat treatment method thereof. By optimizing the alloy composition and heat treatment process, a cast aluminum-magnesium-lithium alloy with excellent performance, simple preparation process and low cost is obtained, which is of great significance for the promotion and application of cast aluminum-magnesium-lithium alloy in the fields of automobile, aerospace, military industry and so on.

The purpose of the present invention is achieved through the following technical solutions:

In the first aspect, the present invention relates to a cast aluminum-magnesium-lithium alloy containing Zn. The alloy includes the following components in weight percent: 2.1-2.5wt% Mg, 3.1-3.5wt% Li, 0.1-1.0wt% Zn , the total amount of impurity elements is less than 0.15wt%, and the balance is Al. In the system of the present invention, if the content of Mg is higher than 2.5wt%, a large number of primary phases will be produced inside the alloy, which is difficult to dissolve into the matrix through solid solution treatment, which will endanger the mechanical properties of the alloy. If the content of Mg is lower than 2.1 wt%, the solid solution strengthening effect of Mg element is not obvious; if the Li content is higher than 3.5wt%, it will cause the alloy to absorb gas easily during the smelting process, resulting in casting defects such as oxidation slag inclusions, such as low Li content If the content of Zn is higher than 3.1wt%, the effect of Li element on improving the specific strength and specific stiffness of the Al alloy cannot be fully exerted; if the content of Zn is higher than 1.0wt%, the density of the alloy will be significantly increased, and if the content of Zn is lower than 0.1wt%, it will not be able to The microstructure and mechanical properties of the alloy are affected.

Preferably, the impurity elements include one or more of Fe, Si, K and Na.

In the second aspect, the present invention also relates to a heat treatment method for cast aluminum-magnesium-lithium alloy containing Zn, including three-stage solid solution treatment and single-stage aging treatment.

Preferably, the three-stage solution treatment includes: solution treating the Zn-containing cast aluminum-magnesium-lithium alloy at 430-440°C for 20-30h, then solution-treating at 500-510°C for 10-20h, and finally Solution treatment at 560-570°C for 20-30 hours. In the system of the present invention, if the solution treatment temperature at each stage is lower than the above temperature range, the corresponding primary phases Al ₁₇ Mg ₁₂ , Al ₂ MgLi, AlLi, etc. cannot be dissolved into the matrix because the temperature is too low. If the solution treatment temperature at each stage is higher than the above temperature range, the alloy is likely to be over-burned or the grains grow excessively due to the high temperature.

Preferably, the single-stage aging treatment is carried out at 175-200° C. for 8-128 hours.

Compared with the prior art, the present invention has the following beneficial effects:

(1) Li is the lightest metal element with a density of only 0.53g cm ^-3 , and it is one of the few elements with high solid solubility in Al. At the eutectic temperature (602°C), about 4.2wt% of Li can be dissolved in Al. In addition, during the aging process, the Li element can be precipitated in the form of Al ₃ Li phase, which plays an aging strengthening effect. The Li element content designed in this patent is 3.1-3.5 wt%, which can greatly reduce the alloy density and improve the alloy strength.

(2) The addition of Mg element can not only further reduce the alloy density, but also play the role of solid solution strengthening, while reducing the solubility of Li in Al, promoting the precipitation of the main strengthening phase Al ₃ Li phase, and increasing the aging strengthening effect.

(3) The addition of Zn element can not only play the role of solid solution strengthening, but also refine the grains and improve the mechanical properties of the alloy.

(4) Three-stage solid solution process is adopted, so that the Al ₈ Mg ₅ phase is solid-dissolved into the matrix at the lower first-stage temperature, the Al ₂ MgLi phase is dissolved at the second-stage temperature, and the AlLi phase is dissolved at the highest third-stage temperature. It dissolves at the low-grade temperature, which solves the problem that the primary phase is difficult to dissolve under the low-temperature single-stage solid solution condition, and the alloy is severely over-burned under the high-temperature single-stage solid solution condition, and at the same time, it effectively avoids the excessive growth of the grain size.

Description of drawings

Other characteristics, objects and advantages of the present invention will become more apparent by reading the detailed description of non-limiting embodiments made with reference to the following drawings:

Fig. 1 is alloy metallographic structure photo in embodiment 1, and wherein Fig. 1 (a) is as-cast metallographic structure photo, Fig. 1 (b) is solid solution state metallographic structure photo;

Fig. 2 is alloy metallographic structure photo in embodiment 2, and wherein Fig. 2 (a) is as-cast metallographic structure photo, Fig. 2 (b) is solid solution state metallographic structure photo;

Fig. 3 is the metallographic structure photo of the alloy in comparative example 1 and comparative example 2, wherein Fig. 3 (a) is the metallographic structure photo of the alloy in the comparative example 1, and Fig. 3 (b) is the alloy solid solution in the comparative example 2 state metallographic structure photos.

Figure 4 is a photo of the metallographic structure of the alloy in Comparative Example 3.

Detailed ways

The present invention will be described in detail below in conjunction with specific embodiments. The following examples will help those skilled in the art to further understand the present invention, but do not limit the present invention in any form. It should be noted that those skilled in the art can make several changes and improvements without departing from the concept of the present invention. These all belong to the protection scope of the present invention.

Example 1

This embodiment relates to a Zn-containing cast aluminum-magnesium-lithium alloy. The alloy includes the following components in weight percent: 2.1wt% Mg, 3.1wt% Li, 0.1wt% Zn, impurity elements Fe, Si, K and The total amount of Na is less than 0.15wt%, and the balance is Al.

The preparation method of the Zn-containing cast Al-Mg-Li alloy is divided into two processes of smelting and heat treatment.

Described smelting process comprises the steps:

1. Prepare raw materials according to the weight percentage of the Zn-containing cast aluminum-magnesium-lithium alloy;

2. Put the pure aluminum into the crucible and melt it. After the furnace temperature rises to 760-780°C, add pure Zn;

3. Add pure Mg when the furnace temperature drops to 730-740°C;

4. Add pure Li under argon protection when the temperature continues to drop to 700-710°C;

5. Controlling the furnace temperature to rise to 720-730°C, refining, removing slag, and pouring to obtain Zn-containing cast aluminum-magnesium-lithium alloy ingots.

Figure 1(a) is a photograph of the as-cast metallographic structure of the alloy in this example. It can be seen that the grains of the as-cast alloy are dendritic, and the coarse primary phases are distributed in the grain boundary in the form of a network.

The heat treatment process includes two steps of three-stage solution treatment and single-stage aging treatment:

The three-stage solution treatment process includes: solution treating the Zn-containing cast Al-Mg-Li alloy at 430° C. for 20 hours, then solution treating it at 500° C. for 10 hours, and finally performing solution treatment at 560° C. for 20 hours. Figure 1(b) is a photograph of the metallographic structure of the alloy in solid solution state in this example. It can be seen from the figure that after three-stage solution treatment, the primary phase in the alloy has been fully dissolved in the matrix.

The single-stage aging treatment process is heat preservation at 175° C. for 64 hours.

Example 2

This embodiment relates to a Zn-containing cast aluminum-magnesium-lithium alloy. The alloy includes the following components in weight percent: 2.1wt% Mg, 3.1wt% Li, 1.0wt% Zn, impurity elements Fe, Si, K and The total amount of Na is less than 0.15wt%, and the balance is Al.

The preparation method of the Zn-containing cast Al-Mg-Li alloy is divided into two processes of smelting and heat treatment.

Described smelting process comprises the steps:

1. Prepare raw materials according to the weight percentage of the Zn-containing cast aluminum-magnesium-lithium alloy;

2. Put the pure aluminum into the crucible and melt it. After the furnace temperature rises to 760-780°C, add pure Zn;

3. Add pure Mg when the furnace temperature drops to 730-740°C;

4. Add pure Li under argon protection when the temperature continues to drop to 700-710°C;

5. Controlling the furnace temperature to rise to 720-730°C, refining, removing slag, and pouring to obtain Zn-containing cast aluminum-magnesium-lithium alloy ingots.

Fig. 2 (a) is the metallographic structure photograph of alloy in the as-cast state in the present embodiment, and the as-cast alloy crystal grain is equiaxed grain, compares with the metallographic structure of alloy as-cast state in the embodiment 1 shown in Fig. 1 (a), can It can be seen that increasing the Zn element content can effectively refine the grains.

The heat treatment process includes two steps of three-stage solution treatment and single-stage aging treatment:

The three-stage solution treatment process includes: solution treating the Zn-containing cast Al-Mg-Li alloy at 430° C. for 20 hours, then solution treating it at 510° C. for 20 hours, and finally performing solution treatment at 560° C. for 20 hours. Figure 2(b) is a photograph of the metallographic structure of the alloy in solid solution state in this example. It can be seen from the figure that after three-stage solution treatment, the primary phase in the alloy has been fully dissolved in the matrix.

The single-stage aging treatment process is heat preservation at 175° C. for 128 hours.

Example 3

This embodiment relates to a Zn-containing cast aluminum-magnesium-lithium alloy. The alloy includes the following components in weight percent: 2.5wt% Mg, 3.5wt% Li, 0.5wt% Zn, impurity elements Fe, Si, K and The total amount of Na is less than 0.15wt%, and the balance is Al.

The preparation method of the Zn-containing cast Al-Mg-Li alloy is divided into two processes of smelting and heat treatment.

Described smelting process comprises the steps:

1. Prepare raw materials according to the weight percentage of the Zn-containing cast aluminum-magnesium-lithium alloy;

2. Put the pure aluminum into the crucible and melt it. After the furnace temperature rises to 760-780°C, add pure Zn;

3. Add pure Mg when the furnace temperature drops to 730-740°C;

4. Add pure Li under argon protection when the temperature continues to drop to 700-710°C;

5. Controlling the furnace temperature to rise to 720-730°C, refining, removing slag, and pouring to obtain Zn-containing cast aluminum-magnesium-lithium alloy ingots.

The heat treatment process includes two steps of three-stage solution treatment and single-stage aging treatment:

The three-stage solution treatment process includes: solution treating the Zn-containing cast Al-Mg-Li alloy at 440° C. for 30 hours, then solution treating it at 510° C. for 20 hours, and finally performing solution treatment at 570° C. for 30 hours.

The single-stage aging treatment process is heat preservation at 200° C. for 8 hours.

Comparative example 1

This comparative example involves a Zn-containing cast aluminum-magnesium-lithium alloy. The composition and aging process of the alloy are basically the same as those in Example 1, the only difference being that the alloy in this comparative example adopts a low-temperature single-stage solution treatment process , specifically 500°C/50h. It can be seen from Figure 3(a) that the primary phase is difficult to dissolve due to the low solid solution temperature.

Comparative example 2

This comparative example relates to a Zn-containing cast aluminum-magnesium-lithium alloy. The composition and aging process of the alloy are basically the same as those in Example 1, the only difference being that the alloy in this comparative example adopts a high-temperature single-stage solution treatment process , specifically 560°C/50h. It can be seen from Figure 3(b) that due to the high solution temperature, the alloy appears overburned.

Comparative example 3

This comparative example relates to a Zn-containing cast aluminum-magnesium-lithium alloy. The composition and aging process of the alloy are basically the same as those in Example 1, the only difference being that the alloy in this comparative example adopts a bipolar solution treatment process. Specifically: solution treatment at 500°C for 20 hours, and then solution treatment at 560°C for 30 hours. It can be seen from Figure 4 that due to the lack of a low-temperature solution treatment step, the alloy is treated at a high temperature for a long time, and the grains grow significantly.

Performance Testing

The mechanical properties of the cast Al-Mg-Li alloy T6 state at room temperature prepared in Example 1-3 and Comparative Example 1-2 are shown in Table 1 below:

Table 1

Test items Example 1 Example 2 Example 3 Comparative example 1 Comparative example 2 Comparative example 3 Yield strength/MPa 242 269 257 231 226 240 Tensile strength/MPa 357 385 372 326 274 353 Elongation/% 5.6 5.2 4.6 3.2 1.8 4.3 Density/g cm^-3 2.453 2.476 2.421 2.453 2.453 2.453

Specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art may make various changes or modifications within the scope of the claims, which do not affect the essence of the present invention. In the case of no conflict, the embodiments of the present application and the features in the embodiments can be combined with each other arbitrarily.

Claims (3)

1. one kind casts magnalium lithium alloy containing Zn, which is characterized in that the alloy includes each group of following weight percent content Point: 2.1~2.5wt%Mg, 3.1~3.5wt%Li, 0.1~1.0wt%Zn, impurity element total amount are less than 0.15wt%, surplus For Al；

The preparation method of the casting magnalium lithium alloy containing Zn is divided into melting and heat treatment；The heat treatment includes at three-stage solution Reason and single-stage aging processing；The three-stage solution processing includes: to cast magnalium lithium alloy at 430~440 DEG C containing Zn for described 20~30h of solution treatment, then 10~20h of solution treatment at 500~510 DEG C, the finally solution treatment 20 at 560~570 DEG C ~30h.

2. casting magnalium lithium alloy containing Zn as described in claim 1, which is characterized in that the impurity element includes Fe, Si, K One or more of with Na.

3. casting magnalium lithium alloy containing Zn as described in claim 1, which is characterized in that single-stage aging processing for 175~ 8~128h is kept the temperature at 200 DEG C.