Heat-treatment-free high-toughness Al-Si series cast aluminum alloy as well as preparation method and application thereof

Abstract

The invention relates to a heat-treatment-free high-toughness Al-Si series cast aluminum alloy and a preparation method and application thereof, and belongs to the field of aluminum alloys. The heat-treatment-free high-toughness Al-Si series cast aluminum alloy comprises, by mass, 6%-9% of Si, 0.1%-0.5% of Mg, 0.001%-1.2% of Cu, 0.15%-0.5% of Fe, 0.001%-0.5% of Mn, 0.001%-0.5% of Mo, 0.015%-0.025% of Sr, 0.001%-0.05% of Ca and the balance Al and inevitable impurities, the sum of the mass fractions of the impurities is smaller than or equal to 0.2%, and the mass fraction of a single impurity element is smaller than or equal to 0.05%. According to the Al-Si series heat-treatment-free cast aluminum alloy prepared through the method, in the cast state, the yield strength ranges from 110 MPa to 140 MPa, the tensile strength ranges from 220 MPa to 265 MPa, and the elongation ranges from 7% to 14%. In addition, the preparation method is simple, the performance is excellent, the alloy is suitable for large integrated die-casting automobile structural parts, in addition, the tolerance of the alloy to the Fe element is high, secondary aluminum can be directly used for production, energy consumption is reduced, and the alloy is suitable for large-scale popularization.

Description

Technical Field

[0001] The present invention relates to the technical field of aluminum alloys, and in particular to a heat-treatment-free high-strength and tough Al-Si series casting aluminum alloy and a preparation method and application thereof. Background Art

[0002] As energy conservation and emission reduction become a major trend, "automobile lightweighting" has become the main goal of the automotive industry, which makes aluminum alloy the preferred material for lightweighting. Al-Si casting alloys have good casting properties and wear resistance, good corrosion resistance and weldability, small thermal expansion coefficient and low shrinkage. They are the most widely used casting aluminum alloys. Mg or Cu can be appropriately added to improve the mechanical properties and heat resistance of the alloy. They are widely used in the field of automotive structural parts, such as body structure, battery housing and gearbox, etc., and have become one of the widely used materials in "automobile lightweighting". The one-piece die-casting process further improves the production efficiency of the automotive industry, while increasing the recycling rate of materials, which has a positive effect on energy conservation and emission reduction, and also puts forward new requirements for materials. Due to the large size of one-piece die-casting parts, if heat treatment is used to improve the performance, it will cause unacceptable deformation, which will have a great impact on the subsequent assembly process. Therefore, heat-treatment-free casting aluminum alloys that do not require heat treatment and can achieve the required performance in the cast state are born as needed. The current heat-treatment-free die-cast aluminum alloy has added more alloying elements, including 9 elements such as Si, Mg, Fe, Cu, and Mn. By adjusting the Cu / Mg ratio, it is ensured that there are more fine Q-Al5Cu2Mg8Si6 phases in the alloy, reducing the negative impact on elongation, and producing a certain second phase strengthening effect to improve its strength. Therefore, the alloy has a higher yield strength in the cast state, but due to the excessive element types and content, its elongation is not high, only about 6%. The AlSi9MgMn alloy (patent publication number: CN114411020A) developed by Shanghai Jiaotong University, in addition to retaining the good casting performance and thermal cracking resistance of the Al-Si casting alloy, adds Sr to modify the eutectic Si, and adds V and RE elements to further refine the eutectic Si, so that the alloy has high strength and toughness characteristics under the condition of containing a higher Si content. However, the large addition of Sr elements often leads to a large number of pores in the ingot, and a small amount of addition cannot achieve the modification effect. At the same time, the large addition of RE elements will also increase the production cost.

[0003] Therefore, optimizing the alloy formula and casting process and reducing the amount of intermetallic compounds in the alloy, especially the needle-shaped Fe-containing intermetallic compounds, are essential for improving the elongation and strength of the alloy in the cast state. Summary of the invention

[0004] In order to solve the above technical problems, the present invention provides a heat-treatment-free high-strength and tough Al-Si cast aluminum alloy and its preparation method and application. Under the premise of ensuring that the alloy has good casting performance, the alloy has good comprehensive mechanical properties in the cast state, thereby meeting the performance requirements of automotive structural parts, especially large thin-walled structural parts.

[0005] The present invention is achieved through the following technical solutions:

[0006] The first object of the present invention is to provide a high-strength and tough Al-Si cast aluminum alloy that does not require heat treatment. The constituent elements of the high-strength and tough Al-Si cast aluminum alloy that does not require heat treatment include Si 6% to 9%, Mg 0.1% to 0.5%, Cu 0.001% to 1.2%, Fe 0.15% to 0.5%, Mn 0.001% to 0.5%, Mo 0.001% to 0.5%, Sr 0.015%-0.025%, Ca 0.001%-0.05%, and the rest are Al and unavoidable impurities, the sum of the mass fractions of the impurities is ≤0.2%, and the mass fraction of a single impurity element is ≤0.05%.

[0007] Preferably, the mass fraction of Si element is 6.5% to 7.5%.

[0008] In one embodiment of the present invention, the sum of the mass fractions of Mn and Mo in the aluminum alloy is ≤0.5%, and the mass ratio of (Mn+Mo) / Fe is 0.2 to 3. Preferably, (Mn+Mo) / Fe=0.3 to 2.1.

[0009] In one embodiment of the present invention, the sum of the mass fractions of Cu and Mg in the aluminum alloy is ≥ 0.7%, and the mass ratio of Cu / Mg is 1 to 5. Preferably, the sum of the mass fractions of Cu and Mg is ≥ 0.9%.

[0010] In one embodiment of the present invention, the alloy has a yield strength of 110 MPa to 140 MPa, a tensile strength of 220 MPa to 265 MPa, and an elongation of 7% to 14% in the cast state.

[0011] The second object of the present invention is to provide a method for preparing the heat-treatment-free high-strength and tough Al-Si cast aluminum alloy, comprising the following steps:

[0012] (1) According to the mass percentage, the raw materials of pure Al, pure Mg, pure Cu, Al-20Si master alloy, Al-10Mn master alloy, Al-20Fe master alloy and Al-5Mo master alloy are dried for later use;

[0013] (2) In an inert atmosphere, pure Al and Al-20Si master alloy are heated to melt to form an Al-Si alloy melt;

[0014] (3) In an inert atmosphere, the temperature is raised to 750° C. to 760° C., pure Cu and Al-20Fe master alloy are added to the Al-Si alloy melt obtained in step (2), the melt is fully stirred after being completely melted, and the melt is kept at 730° C. to 750° C. for 3 min to 5 min;

[0015] (4) Under an inert atmosphere, the temperature is lowered to 735° C. to 745° C., and the Al-10Mn master alloy and the Al-5Mo master alloy are added to the Al-Si alloy melt obtained in step (3). After the melt is completely melted, the melt is fully stirred and kept warm for 3 min to 5 min.

[0016] (5) In an inert atmosphere, the temperature is further lowered to 700° C. to 710° C., pure Mg is added to the Al-Si alloy melt obtained in step (4), and the melt is fully stirred after being completely melted, and the temperature is kept for 5 min to 10 min;

[0017] (6) in an inert atmosphere, subjecting the Al-Si alloy melt obtained in step (5) to a eutectic Si modification treatment at a temperature range of 710° C. to 720° C. for a modification time of 10 min to 20 min;

[0018] (7) In an inert atmosphere, the Al-Si alloy melt obtained in step (6) is heated to 720° C. to 730° C., degassed, and then introduced into a standing furnace, and slag is removed after standing for 8 min to 10 min;

[0019] (8) The Al-Si melt obtained in step (7) is poured into a mold and allowed to stand until it is completely solidified to obtain an ingot.

[0020] In one embodiment of the present invention, in step (1), the drying temperature is 200°C to 300°C.

[0021] In one embodiment of the present invention, in steps (3) to (5), the raw materials are pressed into the Al-Si alloy melt using a bell jar; after pressing, the raw materials are kept for 1 minute to 3 minutes.

[0022] In one embodiment of the present invention, in step (6), the eutectic Si modification treatment is: adding Sr and Ca composite modifiers to the Al-Si alloy melt; the Sr and Ca composite modifiers are added in the form of Al-10Sr master alloy and Al-10Ca master alloy.

[0023] In one embodiment of the present invention, in step (8), the casting temperature of the Al-Si melt is 700°C to 720°C.

[0024] In one embodiment of the present invention, in step (8), the cooling rate of the mold is ≥300K / s.

[0025] The third object of the present invention is to provide the application of the heat-treatment-free high-strength and tough Al-Si series cast aluminum alloy in the automobile industry.

[0026] Under the premise of not affecting the various properties of the alloy, the present invention has been found based on long-term research that when the Si element is maintained at 6% to 9%, the damage of eutectic Si to the toughness of the alloy can be reduced while ensuring the casting performance of the alloy. More preferably, when the Si element is maintained at 7wt.%, the damage can be better reduced. In addition, by reducing the types of alloy elements added, only elements that have sufficient effects under die-casting conditions are retained, the purpose of reducing the number and size of the second phase in the alloy is achieved, which is beneficial to improving the elongation of the alloy. The present invention regulates the ratio of Mn, Mo and Fe elements through a large number of experimental bases, so that even in the case of a higher Fe content, there is no or only a small amount of needle-shaped Fe-containing intermetallic compounds in the alloy to reduce the damage of the Fe element. Therefore, the alloy of the present invention has a higher tolerance for the Fe element, so that the alloy can be directly produced using recycled aluminum, avoiding the high energy consumption brought about by the use of electrolytic aluminum, further reducing carbon emissions, and has positive significance. At the same time, a large number of experiments have shown that when Cu and Mg elements exist in the matrix in the form of solid solution, the strength can be significantly improved while the effect on the elongation is minimized. Therefore, the present invention regulates the addition amount of Cu and Mg elements to promote more Cu and Mg elements to exist in the matrix in the form of solid solution, thereby improving the strength of the alloy without affecting the elongation.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] The present invention provides a heat-treatment-free high-strength and tough Al-Si series cast aluminum alloy and a preparation method and application thereof. The preparation process is simple and efficient, the cost is low, and the alloy has important industrial application value. By reducing the types of elements added to the alloy, the number and size of intermetallic compounds in the alloy are greatly reduced, ensuring that the alloy has a good elongation in the cast state. By regulating the content of Cu and Mg, on the one hand, it can promote the generation of fine Q-Al5Cu2Mg8Si= phases in the alloy, and on the other hand, it can increase the solid solution content of Cu and Mg in the α-Al matrix, thereby improving the effect of solid solution strengthening and achieving the purpose of improving strength. At the same time, by adding Mo and Mn elements, the morphology of Fe-containing intermetallic compounds is changed from coarse block or needle-like phases to Chinese character shape or short rod shape, thereby improving the Fe tolerance of the alloy, so that the alloy can be directly produced using recycled aluminum, further achieving the purpose of energy saving and emission reduction. At the same time, the cooling rate is increased during the solidification process, the growth of the second phase is inhibited, and finally a finer alloy structure is obtained, so that the Al-Si series heat treatment-free casting aluminum alloy prepared by the present invention has a yield strength of 110MPa-140MPa in the cast state, a tensile strength of 220MPa-265MPa, and an elongation of 7%-14%. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to make the content of the present invention more clearly understood, the present invention is further described in detail below according to specific embodiments of the present invention in conjunction with the accompanying drawings, wherein:

[0030] Figure 1 This is a metallographic picture of the Al-Si series heat-treatment-free cast aluminum alloy in Example 1 of the present invention;

[0031] Figure 2 This is a metallographic picture of the Al-Si series heat-treatment-free cast aluminum alloy in Example 2 of the present invention;

[0032] Figure 3 This is a metallographic picture of the Al-Si series heat treatment-free cast aluminum alloy in Example 3 of the present invention;

[0033] Figure 4 This is a metallographic picture of the Al-Si series heat treatment-free cast aluminum alloy in Example 4 of the present invention;

[0034] Figure 5 This is a metallographic picture of the Al-Si series heat treatment-free cast aluminum alloy in Example 5 of the present invention;

[0035] Figure 6 This is a metallographic picture of the Al-Si series heat-treatment-free cast aluminum alloy in Example 6 of the present invention;

[0036] Figure 7This is a metallographic picture of the Al-Si series heat-treatment-free cast aluminum alloy in Comparative Example 1 of the present invention;

[0037] Figure 8 This is a metallographic picture of the Al-Si series heat-treatment-free cast aluminum alloy in Comparative Example 2 of the present invention;

[0038] Fig. 9 This is a metallographic picture of the Al-Si series heat-treatment-free cast aluminum alloy in Comparative Example 3 of the present invention;

[0039] Fig.10 This is a metallographic picture of the Al-Si series heat-treatment-free cast aluminum alloy in Comparative Example 4 of the present invention. DETAILED DESCRIPTION

[0040] The present invention is further described below in conjunction with the accompanying drawings and specific embodiments so that those skilled in the art can better understand the present invention and implement it, but the embodiments are not intended to limit the present invention.

[0041] The invention aims to provide a heat-treatment-free high-strength and tough Al-Si cast aluminum alloy, wherein the alloy components and mass percentages are: Si 6% to 9%, Mg 0.1% to 0.5%, Cu 0.001% to 1.2%, Fe0.15% to 0.5%, Mn 0.001% to 0.5%, Mo 0.001% to 0.5%, Sr 0.015%-0.025%, Ca0.001%-0.05%, and the rest are Al and unavoidable impurities, and the sum of the mass fractions of the impurity elements is ≤0.2%, and the mass fraction of a single impurity element is ≤0.05%.

[0042] Preferably, the mass fraction of Si element in the alloy is 6.5% to 7.5%.

[0043] Furthermore, the sum of the mass fractions of Mn and Mo elements in the alloy is ≤0.5%, and (Mn+Mo) / Fe=0.2-3.

[0044] Preferably, (Mn+Mo) / Fe=0.3-2.1.

[0045] Furthermore, the sum of the mass fractions of Cu and Mg elements in the alloy is ≥ 0.7%.

[0046] Preferably, the sum of the mass fractions of Cu and Mg elements is ≥ 0.9%.

[0047] Furthermore, the alloy has a yield strength of 110 MPa to 140 MPa, a tensile strength of 220 MPa to 265 MPa, and an elongation of 7% to 14% in the cast state.

[0048] Another object of the present invention is to provide a method for preparing the above-mentioned Al-Si series heat-treatment-free cast aluminum alloy, which method specifically comprises the following steps:

[0049] (1) preparing industrial pure Al (purity ≥ 99.5%), pure Mg (purity > 99.9%), pure Cu (purity > 99.9%), and aluminum-based master alloys such as Al-20Si, Al-10Mn, Al-20Fe, and Al-5Mo as raw materials according to mass percentage, and drying them for later use;

[0050] (2) placing industrial pure Al and Al-20Si master alloy in a graphite crucible and heating them until they are melted to form an Al-Si alloy melt under an argon protective atmosphere;

[0051] (3) In an argon protective atmosphere, the temperature is raised to 750°C to 760°C, pure Cu and Al-20Fe master alloy are added to the Al-Si alloy melt, the melt is fully stirred after being completely melted, and the melt is kept at 750°C for 3min to 5min;

[0052] (4) Under an argon protective atmosphere, the temperature is lowered to 735°C to 745°C, and Al-10Mn and Al-5Mo master alloys are added to the Al-Si alloy melt. After the melt is completely melted, the melt is fully stirred and kept within this temperature range for 3min to 5min.

[0053] (5) Under an argon protective atmosphere, the temperature is further lowered to 700°C to 710°C, pure Mg is added to the Al-Si alloy melt, the melt is fully stirred after being completely melted, and the melt is kept within this temperature range for 5 to 10 minutes;

[0054] (6) Under an argon protective atmosphere, the Al-Si alloy melt is subjected to a eutectic Si modification treatment in a temperature range of 710°C to 720°C for a modification time of 10 min to 20 min;

[0055] (7) In an argon protective atmosphere, the Al-Si alloy melt is heated to 720°C to 730°C, degassed, and then introduced into a standing furnace for 8min to 10min before slagging;

[0056] (8) The Al-Si melt is poured into a mold and allowed to stand until it is completely solidified to produce an ingot.

[0057] Furthermore, in step (1), the raw material is dried at 200°C to 300°C for later use.

[0058] Furthermore, in steps (3) to (5), the raw materials are pressed into the melt using a bell jar and maintained for 1 to 3 minutes after being pressed.

[0059] Furthermore, in steps (2) to (7), the alloy raw material is heated by induction heating in a medium frequency furnace, and the melting temperature is controlled at 650°C to 765°C.

[0060] Furthermore, in steps (2) to (7), the inert atmosphere is an argon protective atmosphere.

[0061] Furthermore, the eutectic Si modification treatment described in step (6) is to add Sr and Ca composite modifiers to the Al-Si alloy melt in the form of Al-10Sr and Al-10Ca intermediate alloys, wherein the total mass of Sr element added is 0.015%-0.025% of the total amount of the alloy elements, and the total mass of Ca element added is 0.001%-0.05% of the total amount of the alloy elements.

[0062] Furthermore, the degassing in step (7) is performed by feeding 0.8-1% of the total amount of hexachloroethane powder into the Al-Si melt using argon gas at a pressure of 0.2 MPa, and the degassing time is 5 min to 10 min.

[0063] Furthermore, before the step (7) is introduced into the static furnace, argon gas at a pressure of 0.1 MPa to 0.2 MPa should be introduced into the static furnace to expel air, so that an argon atmosphere is formed in the static furnace.

[0064] Furthermore, the casting temperature in step (8) is 700°C to 720°C.

[0065] Furthermore, the mold cooling rate described in step (8) should be ≥300K / s.

[0066] The test methods described in the following examples are conventional methods unless otherwise specified; the reagents and materials described are commercially available unless otherwise specified.

[0067] The percentages used in the following examples are by mass unless otherwise specified.

[0068] Example 1

[0069] The present embodiment provides a heat-treatment-free high-strength and toughness Al-Si cast aluminum alloy and a preparation method thereof. The composition and mass percentage of the heat-treatment-free high-strength and toughness Al-Si cast aluminum alloy are as follows: Si 7.1%, Mg 0.25%, Cu0.5%, Fe 0.15%, Mo 0.2%, Mn 0.3%, Sr 0.015%, Ca 0.05%, and the rest are Al and unavoidable impurities, and the sum of the mass fractions of the impurity elements is ≤0.2%, and the mass fraction of a single impurity element is ≤0.05%.

[0070] The preparation method of the above alloy is:

[0071] (1) preparing industrial pure Al (purity ≥ 99.5%), pure Mg (purity > 99.9%), pure Cu (purity > 99.9%) and aluminum-based master alloys such as Al-20Si, Al-10Mn, Al-20Fe, and Al-5Mo as raw materials according to mass percentage, drying them at 200° C. for later use; (2) placing industrial pure Al and Al-20Si master alloys in a graphite crucible and heating them to melt under an argon protective atmosphere to form an alloy melt; (3) heating the temperature to 750° C., adding pure Cu and Al-20Fe master alloys to the alloy melt of step (2), stirring the melt until it is completely melted, and keeping the temperature at 750° C. for 5 min; (4) cooling the temperature to 735° C., adding Al-10Mn and Al-5Mo master alloys to the alloy melt of step (3), and stirring the melt until it is completely melted; and After complete melting, the melt is stirred thoroughly and kept within the temperature range for 5 minutes; (5) The temperature is further lowered to 700°C, and pure Mg is added to the alloy melt of step (4). After complete melting, the melt is stirred thoroughly and kept within the temperature range for 5 minutes; (6) The temperature is raised to 720°C, and Sr and Ca composite modifiers are added to the alloy melt of step (5) to modify the eutectic Si. The modification time is 15 minutes, and the eutectic Si is added in the form of Al-10Sr and Al-10Ca intermediate alloys; (7) The alloy melt of step (6) is heated to 720°C, degassed, and then introduced into a standing furnace. After standing for 10 minutes, slag is removed; (8) The Al-Si melt is poured into a mold at 720°C. The mold cooling rate is 400K / s. The mold is stood until completely solidified to obtain an ingot. Its metallographic structure is as follows: Figure 1 As shown. Figure 1 It can be seen that there are a small amount of Q-Al5Cu2Mg8Si phase and a small amount of short rod-shaped Fe-containing intermetallic compounds in the structure. The high-strength and tough Al-Si series heat-treatment-free cast aluminum alloy of this embodiment is tested with reference to GB / T 228-2002, and the yield strength obtained is 116MPa, the tensile strength is 235MPa, and the elongation is 9.53%.

[0072] Example 2

[0073] This embodiment provides a heat-treatment-free high-strength and toughness Al-Si cast aluminum alloy and a preparation method thereof. The composition and mass percentage of the heat-treatment-free high-strength and toughness Al-Si cast aluminum alloy are as follows: Si 7%, Mg 0.3%, Cu 0.7%, Fe0.15%, Mo 0.2%, Mn 0.3%, Sr 0.025%, Ca 0.001%, and the rest are Al and unavoidable impurities, and the sum of the mass fractions of the impurity elements is ≤0.2%, and the mass fraction of a single impurity element is ≤0.05%.

[0074] The preparation method of the above alloy is basically the same as that of Example 1. The metallographic structure of the alloy ingot is as follows: Figure 2 As shown. Figure 2 It can be seen that there are a small amount of Q-Al5Cu2Mg8Si phase and a small amount of short rod-shaped Fe-containing intermetallic compounds in the structure. The high-strength and tough Al-Si series heat-treatment-free cast aluminum alloy of this embodiment is tested with reference to GB / T 228-2002, and the yield strength is 132MPa, the tensile strength is 254.5MPa, and the elongation is 8.85%.

[0075] Example 3

[0076] This embodiment provides a heat-treatment-free high-strength and toughness Al-Si cast aluminum alloy and a preparation method thereof. The composition and mass percentage of the heat-treatment-free high-strength and toughness Al-Si cast aluminum alloy are as follows: Si 6.8%, Mg 0.3%, Cu 0.7%, Fe 0.3%, Mo 0.1%, Mn 0.001%, Sr 0.02%, Ca 0.025%, and the rest are Al and unavoidable impurities, and the sum of the mass fractions of the impurity elements is ≤0.2%, and the mass fraction of a single impurity element is ≤0.05%.

[0077] The preparation method of the above alloy is basically the same as that of Example 1. The metallographic structure of the alloy ingot is as follows: Figure 3 As shown. Figure 3 It can be seen that eutectic Si is uniformly distributed in the structure. The high-strength and toughness Al-Si series heat-treatment-free cast aluminum alloy of this embodiment was tested with reference to GB / T 228-2002, and the obtained yield strength was 136MPa, the tensile strength was 264MPa, and the elongation was 14.09%.

[0078] Example 4

[0079] This embodiment provides a heat-treatment-free high-strength and toughness Al-Si cast aluminum alloy and a preparation method thereof. The composition and mass percentage of the heat-treatment-free high-strength and toughness Al-Si cast aluminum alloy are as follows: Si 7.9%, Mg 0.25%, Cu 0.5%, Fe 0.15%, Mo 0.2%, Mn 0.3%, Sr 0.022%, Ca 0.012%, and the rest are Al and unavoidable impurities, and the sum of the mass fractions of the impurity elements is ≤0.2%, and the mass fraction of a single impurity element is ≤0.05%.

[0080] The preparation method of the above alloy is basically the same as that of Example 1, except that the mold cooling rate is 500K / s.

[0081] The metallographic structure of the alloy ingot is as follows: Figure 4 As shown. Figure 4It can be seen that there are a large number of reticular and short rod-shaped Fe-containing intermetallic compounds in the structure. The high-strength and tough Al-Si series heat-treatment-free cast aluminum alloy of this embodiment was tested with reference to GB / T 228-2002, and the obtained yield strength was 125MPa, the tensile strength was 254MPa, and the elongation was 12.05%.

[0082] Example 5

[0083] This embodiment provides a heat-treatment-free high-strength and toughness Al-Si cast aluminum alloy and a preparation method thereof. The composition and mass percentage of the heat-treatment-free high-strength and toughness Al-Si cast aluminum alloy are as follows: Si 8.4%, Mg 0.3%, Cu 0.7%, Fe 0.5%, Mo 0.1%, Mn 0.3%, Sr 0.018%, Ca 0.035%, and the rest are Al and unavoidable impurities, and the sum of the mass fractions of the impurity elements is ≤0.2%, and the mass fraction of a single impurity element is ≤0.05%.

[0084] The preparation method of the above alloy is basically the same as that of Example 1. The metallographic structure of the alloy ingot is as follows: Figure 5 As shown. Figure 5 It can be seen that there are a large number of reticular and short rod-shaped Fe-containing intermetallic compounds and a small amount of Q-Al5Cu2Mg8Si phase in the structure. The high-strength and tough Al-Si series heat-treatment-free cast aluminum alloy of this embodiment is tested with reference to GB / T 228-2002, and the yield strength obtained is 142MPa, the tensile strength is 268MPa, and the elongation is 7.32%.

[0085] Example 6

[0086] This embodiment provides a heat-treatment-free high-strength and toughness Al-Si cast aluminum alloy and a preparation method thereof. The composition and mass percentage of the heat-treatment-free high-strength and toughness Al-Si cast aluminum alloy are as follows: Si 7.3%, Mg 0.5%, Cu 0.6%, Fe 0.3%, Mo 0.2%, Mn 0.3%, Sr 0.023%, Ca 0.045%, and the rest are Al and unavoidable impurities, and the sum of the mass fractions of the impurity elements is ≤0.2%, and the mass fraction of a single impurity element is ≤0.05%.

[0087] The preparation method of the above alloy is basically the same as that of Example 1. The metallographic structure of the alloy ingot is as follows: Figure 6 As shown. Figure 6It can be seen that there are a large number of reticular and short rod-shaped Fe-containing intermetallic compounds and a small amount of Q-Al5Cu2Mg8Si phase in the structure. The high-strength and tough Al-Si series heat-treatment-free cast aluminum alloy of this embodiment is tested with reference to GB / T 228-2002, and the yield strength is 139MPa, the tensile strength is 262MPa, and the elongation is 10.46%.

[0088] Comparative Example 1

[0089] This comparative example provides a heat-treatment-free Al-Si cast aluminum alloy and a preparation method thereof. The composition and mass percentage of the heat-treatment-free Al-Si cast aluminum alloy are as follows: Si 7.1%, Mg 0.25%, Cu 0.6%, Fe 0.3%, Mo0.2%, Mn 0.3%, and the rest are Al and unavoidable impurities, and the sum of the mass fractions of the impurity elements is ≤0.2%, and the mass fraction of a single impurity element is ≤0.05%. The preparation method of the above alloy is basically the same as that of Example 1, and the metallographic structure of the alloy ingot is as follows: Figure 7 As shown. Figure 7 It can be seen that there are a lot of lath-shaped eutectic Si in the structure. The Al-Si series heat treatment-free cast aluminum alloy of this comparative example was tested with reference to GB / T 228-2002, and the yield strength was 122MPa, the tensile strength was 247MPa, and the elongation was 3.6%.

[0090] Comparative Example 2

[0091] This comparative example provides a heat-treatment-free Al-Si cast aluminum alloy and a preparation method thereof. The composition and mass percentage of the heat-treatment-free Al-Si cast aluminum alloy are as follows: Si 7%, Mg 0.3%, Cu 0.8%, Fe 0.3%, Mo 0.5%, Mn 0.5%, and the rest are Al and unavoidable impurities, and the sum of the mass fractions of the impurity elements is ≤0.2%, and the mass fraction of a single impurity element is ≤0.05%.

[0092] The preparation method of the above alloy is basically the same as that of Example 1. The metallographic structure of the alloy ingot is as follows: Figure 8 As shown. Figure 8 It can be seen that there are a large number of net-like or long strip-like Fe-containing intermetallic compounds in the structure. The Al-Si series heat-treatment-free cast aluminum alloy of this comparative example was tested with reference to GB / T 228-2002, and the obtained yield strength was 103 MPa, the tensile strength was 217 MPa, and the elongation was 2.33%.

[0093] Comparative Example 3

[0094] This comparative example provides a heat-treatment-free Al-Si cast aluminum alloy and a preparation method thereof. The composition and mass percentage of the heat-treatment-free Al-Si cast aluminum alloy are as follows: Si 6.8%, Mg 0.2%, Cu 0.3%, Fe 0.3%, Mo 0.2%, Mn 0.3%, and the rest are Al and unavoidable impurities, and the sum of the mass fractions of the impurity elements is ≤0.2%, and the mass fraction of a single impurity element is ≤0.05%.

[0095] The preparation method of the above alloy is basically the same as that of Example 1. The metallographic structure of the alloy ingot is as follows: Fig. 9 As shown. Fig. 9 It can be seen that the eutectic Si is unevenly distributed in the structure and there are skeletal Fe-containing compounds. The Al-Si series heat-treatment-free cast aluminum alloy of this comparative example was tested with reference to GB / T 228-2002, and the yield strength obtained was 92MPa, the tensile strength was 201MPa, and the elongation was 4.63%.

[0096] Comparative Example 4

[0097] This comparative example provides a heat-treatment-free Al-Si cast aluminum alloy and a preparation method thereof. The composition and mass percentage of the heat-treatment-free Al-Si cast aluminum alloy are as follows: Si 7.9%, Mg 0.25%, Cu 0.5%, Fe 0.3%, Mo0.2%, Mn 0.3%, and the rest are Al and unavoidable impurities, and the sum of the mass fractions of the impurity elements is ≤0.2%, and the mass fraction of a single impurity element is ≤0.05%.

[0098] The preparation method of the above alloy is basically the same as that of Example 1, except that the mold cooling rate is 50K / s.

[0099] The metallographic structure of the alloy ingot is as follows: Fig.10 As shown. Fig.10 It can be seen that eutectic Si is aggregated in the structure. The Al-Si series heat treatment-free cast aluminum alloy of this comparative example was tested with reference to GB / T 228-2002, and the obtained yield strength was 107 MPa, the tensile strength was 214 MPa, and the elongation was 4.71%.

[0100] Obviously, the above embodiments are merely examples for clear explanation and are not intended to limit the implementation methods. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived from these are still within the protection scope of the invention.

Claims

1. A heat-treatment-free high-strength and tough Al-Si cast aluminum alloy, characterized in that: Measured in percentage by mass, the constituent elements of the heat-treatment-free high-strength and tough Al-Si based cast aluminum alloy include Si 6% to 9%, Mg 0.1% to 0.5%, Cu 0.001% to 1.2%, Fe 0.15% to 0.5%, Mn 0.001% to 0.5%, Mo 0.001% to 0.5%, Sr 0.015%-0.025%, Ca 0.001%-0.05%, and the rest are Al and unavoidable impurities, the sum of the mass fractions of the impurities is ≤0.2%, and the mass fraction of a single impurity element is ≤0.05%.

2. The heat-treatment-free high-strength and tough Al-Si based cast aluminum alloy according to claim 1, characterized in that: The sum of the mass fractions of the Mn element and the Mo element in the aluminum alloy is ≤0.5%, and the mass ratio of (Mn+Mo) / Fe is 0.2-3.

3. The heat-treatment-free high-strength and tough Al-Si based cast aluminum alloy according to claim 1, characterized in that: The sum of the mass fractions of the Cu element and the Mg element in the aluminum alloy is ≥0.7%, and the mass ratio of Cu / Mg is 1-5.

4. The method for preparing the heat-treatment-free high-strength and tough Al-Si cast aluminum alloy according to any one of claims 1 to 3, characterized in that: The following steps are involved: (1) According to the mass percentage, the raw materials of pure Al, pure Mg, pure Cu, Al-20Si master alloy, Al-10Mn master alloy, Al-20Fe master alloy and Al-5Mo master alloy are dried for later use; (2) In an inert atmosphere, pure Al and Al-20Si master alloy are heated to melt to form an Al-Si alloy melt; (3) In an inert atmosphere, the temperature is raised to 750° C. to 760° C., pure Cu and Al-20Fe master alloy are added to the Al-Si alloy melt obtained in step (2), the melt is fully stirred after being completely melted, and the melt is kept at 730° C. to 750° C. for 3 min to 5 min; (4) Under an inert atmosphere, the temperature is lowered to 735° C. to 745° C., and the Al-10Mn master alloy and the Al-5Mo master alloy are added to the Al-Si alloy melt obtained in step (3). After the melt is completely melted, the melt is fully stirred and kept warm for 3 min to 5 min. (5) In an inert atmosphere, the temperature is further lowered to 700° C. to 710° C., pure Mg is added to the Al-Si alloy melt obtained in step (4), and the melt is fully stirred after being completely melted, and the temperature is kept for 5 min to 10 min; (6) in an inert atmosphere, subjecting the Al-Si alloy melt obtained in step (5) to a eutectic Si modification treatment at a temperature range of 710° C. to 720° C. for a modification time of 10 min to 20 min; (7) In an inert atmosphere, the Al-Si alloy melt obtained in step (6) is heated to 720° C. to 730° C., degassed, and then introduced into a standing furnace, and slag is removed after standing for 8 min to 10 min; (8) The Al-Si melt obtained in step (7) is poured into a mold and allowed to stand until it is completely solidified to obtain an ingot.

5. The preparation method according to claim 4, characterized in that: In step (1), the drying temperature is 200°C to 300°C.

6. The preparation method according to claim 4, characterized in that: In steps (3) to (5), the raw materials are pressed into the Al-Si alloy melt using a bell jar; after pressing, the raw materials are kept for 1 minute to 3 minutes.

7. The preparation method according to claim 4, characterized in that: In step (6), the eutectic Si modification treatment is: adding Sr and Ca composite modifiers to the Al-Si alloy melt; the Sr and Ca composite modifiers are added in the form of Al-10Sr master alloy and Al-10Ca master alloy.

8. The preparation method according to claim 4, characterized in that: In step (8), the casting temperature of the Al-Si melt is 700°C to 720°C.

9. The preparation method according to claim 4, characterized in that: In step (8), the cooling rate of the mold is ≥300K / s.

10. Application of the heat-treatment-free high-strength and tough Al-Si based cast aluminum alloy according to any one of claims 1 to 3 in the automobile industry.

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