Die-casting aluminium-silicon-zinc-magnesium alloy and its preparation method

Abstract

The application discloses a die-casting aluminum-silicon-zinc-magnesium alloy and a preparation method thereof. The alloy composition is as follows: Si 6.50-9.50%, Zn 0.5-0.8%, Mg 0.25-0.70%, Cu 0.10-0.30%, Mn 0.30-0.70%, Sr 0.01-0.04%, Fe≤0.12%, Ti≤0.01%, other impurity elements≤0.05%, and the rest is Al. The preparation method comprises the following steps: after vacuum die-casting, carrying out baking pretreatment at 100-120 DEG C for 120-240 min, and baking treatment at 175-210 DEG C for 30 min. The application utilizes the promoting effect of zinc element aging separation, and strengthens and improves the plasticity of the alloy through the baking pretreatment and baking treatment, so that the prepared die-casting aluminum-silicon-zinc-magnesium alloy is particularly suitable for high-strength and high-toughness large die-casting parts, and has a wide application prospect in the automobile field.

Description

Technical Field

[0001] This invention belongs to the field of aluminum alloy material technology, specifically relating to a die-cast aluminum-silicon-zinc-magnesium alloy and its preparation method. Background Technology

[0002] Lightweighting of automobiles can effectively improve the driving range of new energy vehicles, greatly promote their development, align with the national strategic goals of energy conservation and emission reduction, and is an inevitable trend in the automotive industry. Aluminum alloys have advantages such as low density, high specific strength, and corrosion resistance, making them a widely used lightweight material in the automotive industry and aerospace.

[0003] Die casting is one of the main forming methods for aluminum alloy components, especially in the automotive field. Die-cast aluminum alloy parts are lightweight, thin-walled, and possess high strength and surface hardness, meeting the requirements of lightweight automotive manufacturing and leading to their rapid development in automotive parts applications. AlSi alloys are commonly used die-cast aluminum alloy materials, widely applied in die castings due to their excellent casting performance and corrosion resistance. For high-vacuum die-cast AlSi alloys, T6 heat treatment can be used for strengthening. With the integrated design of automotive parts, automotive aluminum alloy die castings are developing towards larger, more complex, and thinner-walled components. The solution treatment followed by quenching during T6 heat treatment can easily cause deformation of large, complex, thin-walled die-cast aluminum alloy components, making subsequent assembly impossible. Therefore, current technology mainly avoids T6 heat treatment for strengthening after die casting, instead directly using the as-cast parts and utilizing subsequent low-temperature baking in the automotive process for further strengthening. However, these AlSi-based as-cast die-cast alloys have lower mechanical properties compared to T6 heat-treated die-cast aluminum alloys. For example, the yield strength of the as-cast AlSi die-cast alloy disclosed in patent CN201910449860.6 is 130-150 MPa, which is much lower than the yield strength (210-280 MPa) of the T6-state Silafont-36 die-cast alloy. Therefore, it is essential to develop a large, complex, thin-walled die-cast part with high yield strength and tensile strength without high-temperature heat treatment. Summary of the Invention

[0004] In order to overcome the shortcomings and disadvantages of the prior art, the primary objective of this invention is to provide a method for preparing die-cast aluminum-silicon-zinc-magnesium alloy. This method, through a high-vacuum die-casting process, can produce die-cast aluminum-silicon-zinc-magnesium alloys that can be used in high-toughness die-cast parts that meet the requirements of lightweight automobiles.

[0005] In view of the problems that existing die-cast aluminum-silicon alloys have insufficient as-cast mechanical properties and that large thin-walled die-cast parts cannot be strengthened by T6 heat treatment, the second objective of this invention is to provide a die-cast aluminum-silicon-zinc-magnesium alloy prepared by the preparation method described above.

[0006] The primary objective of this invention can be achieved through the following technical solution:

[0007] A method for preparing a die-cast aluminum-silicon-zinc-magnesium alloy includes the following preparation steps:

[0008] (1) Ingredients: Prepare the raw materials according to the following mass percentages.

[0009]

[0010] (2) Melting: After preheating the above raw materials to remove moisture, add them to the melting furnace according to the degree of burn-off, and gradually raise the temperature to 720-735℃ to melt all the raw materials.

[0011] (3) Die casting: The mold is pre-sprayed with release agent and preheated to 180°C. Under vacuum conditions, the temperature of the alloy melt is controlled within the range of 695°C to 710°C to carry out die casting to obtain die casting parts.

[0012] (4) Heat treatment: After cooling the die casting in step (3), perform pre-baking treatment at a temperature of 100-120℃ and a time of 120-240 min, and then perform baking treatment at a temperature of 175-210℃ and a time of 30 min to prepare die casting aluminum-silicon-zinc-magnesium alloy.

[0013] The main components and mass percentages of the die-cast aluminum-silicon-zinc-magnesium alloy are as follows: Si 7.50~8.50%, Zn 0.5~0.8%, Mg 0.25~0.70%, Cu 0.10~0.30%, Mn 0.30~0.70%, Sr 0.01~0.04%, Fe≤0.12%, Ti≤0.01%, other impurity elements≤0.05%, and the remainder is Al.

[0014] Preferably, the specific steps of the smelting in step (2) are as follows: After preheating the above raw materials to remove moisture, first add industrial pure Al to the melting furnace, gradually raise the temperature to 750°C, and after all the industrial pure Al has melted, add Al-Si20 master alloy, Al-Mn10 master alloy and Al-Cu50 master alloy in sequence, stir after melting, lower the temperature to 720°C, then add Al-Zn30 master alloy, Al-Mg50 master alloy and Al-Sr10 master alloy, stir after melting, then add refining agent to the alloy melt for refining, degas with inert gas, remove the slag on the surface of the melt after standing, and obtain the alloy melt;

[0015] Preferably, the mass ratio of the refining agent to the raw material is 4:1000.

[0016] Preferably, the vacuum degree of the vacuum condition described in step (3) is ≤60mbar.

[0017] Preferably, the heating rate of the pre-baking treatment and baking treatment in step (4) is 10℃ / min, and the cooling method is air cooling.

[0018] The second objective of this invention is achieved through the following technical solution:

[0019] A die-cast aluminum-silicon-zinc-magnesium alloy is prepared according to the above-described method for preparing die-cast aluminum-silicon-zinc-magnesium alloys. Compared with existing die-cast aluminum alloys, this invention has the following significant advantages:

[0020] (1) The die-cast aluminum-silicon-zinc-magnesium alloy of the present invention has both high strength and plasticity after pretreatment before baking and baking treatment. The designed alloy has a yield strength of 200-245 MPa, a tensile strength of 325-340 MPa and an elongation of 10%-14% after pretreatment before baking and baking treatment.

[0021] (2) The die-cast aluminum-silicon-zinc-magnesium alloy of the present invention can achieve high strength after low-temperature pretreatment and short-time baking. Compared with traditional T6 heat treatment, it avoids blistering and quenching deformation on the surface of the die casting during the solution treatment process, and is particularly suitable for strengthening large thin-walled die castings. The introduction of pretreatment before baking can promote the formation of GP zone, forming a high-density nano-strengthening phase during the subsequent baking process. In addition, it can reduce the residual stress inside the die casting, thereby improving the plasticity of the alloy after baking treatment.

[0022] (3) The die-cast aluminum-silicon-zinc-magnesium alloy material of the present invention is formulated by industrial pure Al, Al-Si20 master alloy, Al-Mg50 master alloy, Al-Cu50 master alloy, Al-Mn10 master alloy, Al-Zn30 master alloy and Al-Sr10 master alloy. It does not contain high-cost alloying elements such as rare earth, Mo, Co, Ni and Ti, and is low in cost and suitable for large-scale production.

[0023] (4) The zinc content of the die-cast aluminum-silicon-zinc-magnesium alloy of the present invention is 0.5-0.8%. The addition of zinc significantly improves the baking strengthening effect of the alloy. In addition, the atomic clusters formed by zinc during the die-casting process can decompose during the pretreatment process, increase the concentration of matrix solute, promote the formation of nano-precipitates, and improve the final yield strength of the casting. Attached Figure Description

[0024] Figure 1 This is a transmission electron micrograph of the nano-precipitated phases in the matrix of the alloy in Example 2 of the present invention after it has been baked at 195°C for 30 min.

[0025] Figure 2 This is a transmission electron micrograph of the nano-precipitated phase in the matrix of the alloy in Example 2 of the present invention after pretreatment at 105°C for 240 min and subsequent baking at 195°C for 30 min. Detailed Implementation

[0026] The present invention will be further described in detail below with reference to the embodiments and accompanying drawings, but the embodiments of the present invention are not limited thereto.

[0027] Example 1

[0028] Step (1): Prepare ingredients according to Table 1

[0029] Table 1. Ingredient list of alloy in Example 1

[0030]

[0031]

[0032] Step (2): Smelting

[0033] First, pure aluminum ingots are added to the melting furnace, and the temperature is increased by 145°C per hour until it reaches 750°C. After all the pure aluminum ingots have melted, Al-Si20 master alloy, Al-Mn10 master alloy, and Al-Cu50 master alloy are added in sequence. After melting, the mixture is stirred for 5 minutes to ensure uniform alloy composition. To prevent the low-melting-point master alloys from burning off, the melt temperature is lowered to 720°C, and then Al-Zn30, Al-Mg50, and Al-Sr10 master alloys are added. After melting, the mixture is stirred for 5 minutes. Then, a refining agent (purchased from Luyuan Metal Materials Co., Ltd.) is added to the molten aluminum at a ratio of 0.4%. The mixture is refined at 720–735°C and degassed with high-purity argon. After standing for 15 minutes, the slag is skimmed off. A sample is taken at the furnace to test the chemical composition of the melt. Once the composition is qualified, it is ready for die casting.

[0034] Step (3): Die casting

[0035] Preheat the mold to 180°C by spraying release agent on it beforehand. Control the temperature of the molten aluminum within the range of 695°C to 710°C. Perform die casting when the vacuum degree of the cavity is ≤60mbar. After the die casting has cooled, perform pretreatment and baking before baking.

[0036] Step (4): Heat treatment

[0037] The heat treatment included three methods: pre-treatment before baking, baking treatment, and pre-treatment before baking followed by baking. The heating rate for both pre-treatment and baking was 10℃ / min, and the cooling method was air cooling. Table 2 shows the different baking treatment processes and their corresponding mechanical properties. The results in the table show that the yield strength of the alloy improved after pre-treatment and baking treatment, and the elongation of the alloy after short-time pre-treatment also improved. The die-cast parts obtained through the above steps contained Si: 8.32%, Mg: 0.27%, Cu: 0.15%, Mn: 0.35%, Zn: 0.71%, Sr: 0.04%, Fe: 0.11%, other impurity elements 0.032%, and the remainder being Al.

[0038] The mechanical properties of the die-cast and heat-treated parts in this embodiment are shown in Table 2.

[0039] Table 2 Mechanical properties of the alloy in Example 1 in the die-cast state and after different baking treatments

[0040]

[0041] Example 2

[0042] Step (1): Prepare ingredients according to Table 3

[0043] Table 3. Ingredient list of alloy in Example 2

[0044]

[0045] Step (2): Smelting

[0046] First, pure aluminum ingots are added to the melting furnace, and then the temperature is increased by 145°C per hour until it reaches 750°C. After all the pure aluminum ingots have melted, Al-Si20 master alloy, Al-Mn10 master alloy, and Al-Cu50 master alloy are added in sequence. After melting, the mixture is stirred for 5 minutes to ensure uniform alloy composition. The melt temperature is then lowered to 720°C, and Al-Zn30, Al-Mg50, and Al-Sr10 master alloys are added. After melting, the mixture is stirred for 5 minutes. Then, a refining agent is added to the aluminum liquid at a ratio of 0.4%, and the mixture is refined at 720–735°C. High-purity argon gas is used for degassing, and the mixture is allowed to stand for 15 minutes before slag is skimmed off. A sample is taken at the furnace to test the chemical composition of the melt. Once the composition is qualified, it is ready for die casting.

[0047] Step (3): Die casting

[0048] Preheat the mold to 180°C by spraying release agent on it beforehand. Control the temperature of the molten aluminum within the range of 695°C to 710°C. Perform die casting when the cavity vacuum degree is ≤60mbar. After the die casting has cooled, perform heat treatment.

[0049] Step (4): Heat treatment

[0050] The heat treatment included three methods: pretreatment before baking, baking treatment, and pretreatment before baking followed by baking. The heating rate for pretreatment and baking was 10℃ / min, and the cooling method was air cooling. The different baking treatment processes and their corresponding mechanical properties are shown in Table 4. The results in the table show that the yield strength of the alloy improved after baking pretreatment and baking, and the elongation of the alloy after short-time pretreatment also improved. The die-cast parts obtained through the above steps contain Si: 7.94%, Mg: 0.51%, Cu: 0.12%, Mn: 0.50%, Zn: 0.66%, Sr: 0.03%, Fe: 0.10%, other impurity elements 0.026%, and the remainder being Al.

[0051] Figure 1 This is a transmission electron micrograph of the nano-precipitated phases in the matrix of the alloy in Example 2 of the present invention after it has been baked at 195°C for 30 min. Figure 2 This is a transmission electron micrograph of the nano-precipitates in the matrix of the alloy in Example 2 of the present invention after pretreatment at 105°C for 240 min and subsequent baking at 195°C for 30 min.

[0052] from Figure 1 and Figure 2 It can be seen that the number density of nano-precipitates is significantly increased after the pretreatment before baking and the subsequent short-time baking, indicating that the pretreatment before baking can effectively promote the formation of nano-precipitates.

[0053] The mechanical properties of the die-cast and heat-treated parts in this embodiment are shown in Table 4.

[0054] Table 4 Mechanical properties of the alloy in Example 2 in the die-cast state and after different baking treatments

[0055]

[0056]

[0057] Example 3

[0058] Step (1): Prepare ingredients according to Table 5

[0059] Table 5. Ingredient list of alloy in Example 3

[0060]

[0061] Step (2): Smelting

[0062] First, pure aluminum ingots are added to the melting furnace, and then the temperature is increased by 145°C per hour until it reaches 750°C. After all the pure aluminum ingots have melted, Al-Si20 master alloy, Al-Mn10 master alloy, and Al-Cu50 master alloy are added in sequence. After melting, the mixture is stirred for 5 minutes to ensure uniform alloy composition. The melt temperature is then lowered to 720°C, and Al-Zn30, Al-Mg50, and Al-Sr10 master alloys are added. After melting, the mixture is stirred for 5 minutes. Then, a refining agent is added to the aluminum liquid at a ratio of 0.4%, and the mixture is refined at 720–735°C, followed by degassing with high-purity argon. After standing for 15 minutes, the slag is skimmed off. A sample is taken at the furnace to test the chemical composition of the melt. Once the composition is qualified, it is ready for die casting.

[0063] Step (3): Die casting

[0064] Preheat the mold to 180°C by spraying release agent on it beforehand. Control the temperature of the molten aluminum within the range of 695°C to 710°C. Perform die casting when the cavity vacuum degree is ≤60mbar. After the die casting has cooled, perform heat treatment.

[0065] Step (4): Heat treatment

[0066] The heat treatment includes pretreatment before baking and baking treatment. The heating rate for pretreatment and baking is 10℃ / min, and the cooling method is air cooling. The different baking treatment processes and corresponding mechanical properties are shown in Table 6. The results in the table show that the yield strength of the alloy after baking pretreatment and baking is improved, and the elongation of the alloy is comparable to that of the alloy after baking treatment only.

[0067] The die-cast parts obtained through the above steps contain Si: 7.51%, Mg: 0.64%, Cu: 0.24%, Mn: 0.66%, Zn: 0.75%, Sr: 0.03%, Fe: 0.11%, other impurity elements: 0.028%, and the remainder: Al.

[0068] The mechanical properties of the die-cast and heat-treated parts in this embodiment are shown in Table 6.

[0069] Table 6 Mechanical properties of the alloy in Example 3 in the die-cast and heat-treated states.

[0070]

[0071]

[0072] By comparing the mechanical properties of the die castings prepared in Examples 1-3 and the heat-treated parts under different conditions, it can be seen that the yield strength and tensile strength of the die castings that have only undergone pretreatment or baking after die casting are significantly weaker than those that have undergone both pretreatment and baking. In addition, the strength of the castings obtained when the pretreatment temperature is below 100°C is low, while the elongation is significantly reduced when the pretreatment temperature is above 120°C. The strength begins to decrease when the pretreatment time exceeds 240 min, while the pretreatment time and energy consumption are increased. Therefore, the baking pretreatment temperature is 100-120°C and the time is 120-240 min.

[0073] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A method for producing a die-cast aluminium-silicon-zinc-magnesium alloy, characterized in that It comprises the following preparation steps, (1) batching: the raw materials are prepared according to the following mass percentage, (2) melting: after the above raw materials are preheated to remove moisture, they are added to a melting furnace according to the difficulty of burning loss, gradually heated to 720-735 DEG C to make all the raw materials melt completely; (3) die casting: the mold is pre-sprayed with a mold release agent and preheated to 180 DEG C, and the alloy melt is controlled at a temperature of 695 DEG C-710 DEG C under vacuum conditions to carry out die casting, and the die casting is obtained; (4) heat treatment: the die casting in step (3) is cooled and then pre-treated before baking, the pre-baking temperature is 100-120 DEG C, the time is 120-240 min, and then baking treatment is carried out, the baking temperature is 175-210 DEG C, and the baking time is 30 min, to prepare the die casting aluminum silicon zinc magnesium alloy; The main components and mass percentage of the die casting aluminum silicon zinc magnesium alloy are as follows: Si 7.50-8.50%, Zn 0.5-0.8%, Mg 0.25-0.70%, Cu 0.10-0.30%, Mn 0.30-0.70%, Sr 0.01-0.04%, Fe≤0.12%, Ti≤0.01%, other impurity elements≤0.05%, and the rest is Al; The specific steps of the melting in step (2) are as follows: after the above raw materials are preheated to remove moisture, industrial pure Al is first added to the melting furnace, gradually heated to 750 DEG C, and after the industrial pure Al is completely melted, Al-Si20 intermediate alloy, Al-Mn10 intermediate alloy and Al-Cu50 intermediate alloy are sequentially added, melted and stirred, the temperature is reduced to 720 DEG C, then Al-Zn30 intermediate alloy, Al-Mg50 intermediate alloy and Al-Sr10 intermediate alloy are added, melted and stirred, then a refining agent is added to the alloy melt for refining, inert gas is used for degassing, the surface dross of the melt is removed after standing, and the alloy melt is obtained; The designed cast aluminum silicon zinc magnesium alloy has a yield strength of 200-245 MPa, a tensile strength of 325-340 MPa and an elongation of 10%-14% after pre-baking and baking.

2. The method of producing an aluminum-silicon-zinc-magnesium alloy according to claim 1, characterized by, The mass ratio of the refining agent to the raw materials is 4:1000.

3. The method of producing die-cast aluminum-silicon-zinc-magnesium alloy according to claim 1, characterized by, The vacuum degree of the vacuum condition in step (3) is ≤60 mbar.

4. The method of producing die-cast aluminum-silicon-zinc-magnesium alloy according to claim 1, characterized by, The heating rate of the pre-baking and baking treatment in step (4) is 10 DEG C / min, and the cooling method is air cooling.

5. A die cast aluminium silicon zinc magnesium alloy characterised in that, The die casting aluminum silicon zinc magnesium alloy is prepared by the preparation method according to any one of claims 1-4.

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