Heat-treatment-free die-casting aluminum alloy for high-toughness light-weight large complex structural component and preparation method of heat-treatment-free die-casting aluminum alloy

Abstract

The invention belongs to the technical field of aluminum alloy materials and preparation, and relates to a heat-treatment-free die-casting aluminum alloy for a high-toughness light-weight large complex structural component and a preparation method of the heat-treatment-free die-casting aluminum alloy, the aluminum alloy comprises 8.5-10.5 wt% of silicon, 0.10-0.30 wt% of magnesium, 0.28-0.6 wt% of manganese, 0.08-0.50 wt% of iron, 0.04-0.15 wt% of titanium, 0.08-0.2 wt% of strontium, 0.1-0.2 wt% of zirconium, 0.01-0.03 wt% of lanthanum, 0.005-0.015 wt% of yttrium, less than or equal to 0.054 wt% of chromium, less than or equal to 0.3 wt% of molybdenum, less than or equal to 0.1 wt% of vanadium, less than or equal to 0.6 wt% of zinc and the balance aluminum. And the balance of aluminum and inevitable trace impurities. According to the aluminum alloy, in a 150 DEG C * 1000 h long-time thermal stability volatility test, the long-time thermal stability volatility is low, and when secondary aluminum with a higher proportion is used for production, the anti-fatigue performance is excellent.

Description

Technical Field

[0001] The present invention relates to the technical field of aluminum alloy materials and preparation thereof, and in particular to a heat-treatment-free die-casting aluminum alloy for high-strength, toughness, lightweight, large and complex structural parts and a preparation method thereof. Background Art

[0002] As high-strength and lightweight die-castings continue to grow in size, heat treatment may cause deformation of such large, thin-walled die-castings, which will greatly increase the difficulty of subsequent shaping and the scrap rate. On the one hand, heat-treatment-free die-casting aluminum alloy materials can be used directly in the cast state to avoid the above problems, and on the other hand, they can also reduce the manufacturing cost of parts. In recent years, its development and application have gradually become a research hotspot.

[0003] Chinese patent CN115003832A discloses a die-cast aluminum alloy for structural parts, comprising the following components in mass percentage: 6.0-11.0wt.% silicon, 0.3-0.8wt.% copper, 0.1-0.4wt.% magnesium, 0.3-0.8wt.% manganese, 0.01-0.05wt.% strontium, 0.05-0.15wt.% vanadium, not more than 0.5wt.% iron, not more than 0.15wt.% titanium, not more than 0.03wt.% chromium, remainder Al and incidental impurities. The alloy has a yield strength of at least about 130MPa and a bending angle of at least about 20° at a cross-sectional thickness of 3mm when in the cast state and without further treatment. The alloy has a high strength, a deviation in toughness, and a general balance of strength and toughness, and no corresponding composition design is performed for the long-term thermal stability of the alloy and the related properties after adding recycled aluminum, especially the fatigue resistance.

[0004] Chinese patent CN114164362A discloses a heat-treatment-free high-strength and tough aluminum alloy, the mass percentage of the aluminum alloy components is: Si 8.5-11.5%, Cu 0.05-0.5%, Mg 0.05-0.5%, Mo 0.1-0.5%, Sr 0.005-0.1%, B 0.005-0.1%, Cd 0.05-0.3%, Zr 0.05-0.25%, and the rest is Al and unavoidable impurities. The alloy uses boronization to refine the grains, and uses strontium modification to refine the eutectic silicon. The addition of Mo not only avoids the poisoning phenomenon caused by the simultaneous addition of B and Sr, but also refines the eutectic silicon to a submicron size, greatly improving the strength and toughness of the alloy; at the same time, combined with solid solution strengthening and dispersion strengthening, the alloy is given excellent mechanical properties. The tensile strength of the heat-treatment-free high-strength and tough aluminum alloy component is 300-400MPa, the yield strength is 180-320MPa, and the elongation is 8-21%. The alloy still has the problem of high strength and poor toughness, and the balance of strength and toughness is insufficient. In addition, no corresponding composition design is carried out for the long-term thermal stability of the alloy and the related properties after adding recycled aluminum, especially the fatigue resistance.

[0005] Chinese patent CN112899532A discloses a high-strength and tough aluminum alloy recycled from waste aluminum, which is composed of the following components in mass percentage: Si 8.52-8.74%, Mg 0.35-0.38%, Fe 0.63-0.64%, Cr 0.037-0.043%, Ti0.012-0.016%, Mn 0.034-0.035%, Ni 0.020-0.030%, Ba 0.030-0.040%, C 0.004-0.006%, B 0.005-0.010%, and the balance is Al and impurity elements. The alloy uses waste aluminum as the main raw material to regenerate a high-strength and tough aluminum alloy, realizes the recycling of metal resources such as Al, Si, and Mg, improves the use value of waste aluminum, and reduces the production cost of aluminum alloys. However, the toughness of the alloy is seriously insufficient and cannot meet the toughness requirements of large and complex structural parts. Moreover, the control range of Fe content is too narrow, which makes it difficult to effectively control in actual production, greatly increasing production costs. In addition, no corresponding composition design is carried out for the long-term thermal stability of the alloy and the fatigue resistance after adding recycled aluminum.

[0006] CN116287891A discloses a heat-treatment-free die-casting aluminum alloy. Based on the total weight of the die-casting aluminum alloy, the die-casting aluminum alloy includes: 6.5-8.3 weight % Si, 0.2-0.4 weight % Mg, 0.25-0.50 weight % Cu, 0.09-0.25 weight % Fe, 0.5-0.8 weight % Mn, 0.05-0.20 weight % Ti, 0.02-0.04 weight % Sr, 0.01-0.1 weight % Zr, less than or equal to 0.05 weight % Hf, less than or equal to 0.25 weight % Zn, less than or equal to 0.1 weight % rare earth elements, less than or equal to 0.05 weight % other impurity elements and the remainder Al; wherein the rare earth elements include at least one of La, La and Y; and the ratio of the total weight of Cu and Mg to the total weight of Zr and Hf is less than or equal to 22. The ultimate tensile strength of the die-cast aluminum alloy can be 270-320MPa, the yield strength can be 135-170MPa, the elongation at break is not less than 10%, the parameter HHcs of the thermal cracking tendency is not greater than 50, and the parameter UF of the corrosion resistance is not greater than 3.5mm. Although the toughness of the alloy can meet the use requirements of large integrated die-casting structural parts, the corresponding composition design is not carried out for the long-term thermal stability of the alloy and the fatigue resistance after adding recycled aluminum.

[0007] The existing alloy technology generally has the problem that the long-term thermal stability of the alloy and the mechanical properties after the addition of recycled aluminum, especially the fatigue resistance and insufficient strength-toughness balance, are not fully considered during the alloy design. As a result, the addition rate of scrap aluminum used as raw materials in the production of high-strength, tough and lightweight large structural parts is low, which is not conducive to energy conservation and emission reduction, reducing material costs and recycling. Summary of the invention

[0008] The purpose of the present invention is to overcome the shortcomings of the prior art and provide a high-strength, tough, lightweight, heat-treatment-free die-cast aluminum alloy for large and complex structural parts and a preparation method thereof. By controlling the element ratio, especially simultaneously controlling the total mass percentage of Mn+Fe, the ratio of rare earth elements La / Y, and the total mass percentage of La+2Y, the purity of the alloy melt is significantly improved and the long-term thermal stability fluctuation rate of the aluminum alloy at 150°C*1000h is reduced.

[0009] The purpose of the present invention is achieved by adopting the following technical solutions:

[0010] On the one hand, the present invention provides a heat-treatment-free die-cast aluminum alloy for high-strength, tough, lightweight, large and complex structural parts, which comprises, relative to the total weight of the aluminum alloy: 8.5-10.5wt% silicon, 0.10-0.30wt% magnesium, 0.28-0.6wt% manganese, 0.08-0.50wt% iron, 0.04-0.15wt% titanium, 0.08-0.2wt% strontium, 0.1-0.2wt% zirconium, 0.01-0.03wt% lanthanum, 0.005-0.015wt% yttrium, ≤0.054wt% chromium, ≤0.3wt% molybdenum, ≤0.1wt% vanadium, and ≤0 .6wt%, and the rest are aluminum and inevitable trace impurities, wherein the content of a single element of the trace impurities is ≤0.06wt%, and the total amount of the trace impurities is ≤0.15wt%, wherein the value M of the sum of the total mass percentages of manganese and iron (Mn+Fe) is 0.6-0.8wt%; the ratio of lanthanum to yttrium (La / Y) N is 1.8-2.2, and the value K of the sum of the total mass percentages of lanthanum and twice yttrium (La+2Y) is 0.035-0.05wt%, and the aluminum alloy has a tensile strength of 260-290MPa, a yield strength of 130-150MPa, and an elongation after fracture of 11-15%.

[0011] Furthermore, based on the total weight of the aluminum alloy, the aluminum alloy comprises: 8.6-9.6wt% silicon, 0.20-0.23wt% magnesium, 0.28-0.6wt% manganese, 0.08-0.45wt% iron, 0.08-0.13wt% titanium, 0.12-0.2wt% strontium, 0.1-0.15wt% zirconium, 0.01-0.03wt% lanthanum, 0.01-0.015wt% yttrium, and ≤0.054wt% chromium. t%, molybdenum ≤0.3wt%, vanadium ≤0.1wt%, zinc ≤0.6wt%, and the rest are aluminum and inevitable trace impurities, among which the content of a single element of the trace impurities is ≤0.06wt%, and the total amount of the trace impurities is ≤0.15wt%, among which, the sum of the total mass percentages of manganese and iron, M, is 0.63-0.74wt%; the ratio of lanthanum to yttrium, N, is 2.0, and the sum of the total mass percentages of lanthanum and twice yttrium, K, is 0.04wt%.

[0012] Furthermore, relative to the total weight of the aluminum alloy, it contains: 8.87-9.22wt% silicon, 0.20-0.23wt% magnesium, 0.28-0.6wt% manganese, 0.09-0.42wt% iron, 0.08-0.12wt% titanium, 0.16-0.19wt% strontium, 0.15wt% zirconium, 0.02wt% lanthanum, 0.01wt% yttrium, ≤0.054wt% chromium, ≤0.3wt% molybdenum, ≤0.1wt% vanadium, ≤0.6wt% zinc, and the rest is aluminum and inevitable trace impurities, wherein the content of a single element of the trace impurities is ≤0.06wt%, and the total amount of the trace impurities is ≤0.15wt%, wherein the sum of the total mass percentages of manganese and iron, M, is 0.63-0.74wt%; the ratio N of lanthanum to yttrium is 2.0, and the sum of the total mass percentages of lanthanum and twice yttrium, K, is 0.04wt%.

[0013] According to the characteristics of heat-treatment-free die-casting aluminum alloy materials for high-strength, tough, lightweight and large-scale complex structural parts and the requirements of integrated die-casting process, the present invention reasonably controls the range of each element and strictly controls the proportion of main alloy elements, especially the M value (total content of Mn+Fe) and the N value (La / Y ratio).

[0014] Si is the first main alloying element in the heatless aluminum alloy of the present invention, and its content is controlled at 8.5-10.5wt%, which ensures good filling capacity of the alloy while taking into account strength and toughness. When the silicon content is lower than 8.5wt%, the strength of the alloy does not reach the peak area, and the casting performance of the alloy is biased; when the silicon content is higher than 10.5wt%, the strength increase is limited and the toughness decrease rate increases. Preferably, the silicon content is 8.5-10.5wt%, and 8.6-9.6wt% is further preferred. It should be pointed out that compared with the cost of the related invention patents disclosed, the Si content range in the present invention selects a medium-high value range interval because the inventor has found through a large number of experiments that the filling capacity (flow length) is a key factor in determining the integrated die-casting process window and mold design of large structural parts. The stronger the filling capacity, the wider the process window of integrated die-casting, and the more choices of mold design.

[0015] Mg is the second main alloying element in the heatless aluminum alloy of the present invention, and its content is controlled at 0.10-0.30wt%. Mg will form Mg with Si. 2 Si strengthening phase can significantly improve the room temperature strength of the alloy, but it will also significantly reduce the toughness of the alloy. In the present invention, considering the characteristics of high cooling rate and few casting defects of vacuum integrated die casting, the Mg content is controlled in the range of 0.10-0.30wt%, and the Mg-containing cast Al-Si alloy has the potential to further improve its mechanical properties through heat treatment or natural aging. Within this content range, the toughness and thermal stability of the alloy are taken into account. Preferably, the magnesium content is 0.20-0.23wt%.

[0016] Mn is the third main alloying element in the heatless aluminum alloy of the present invention, and its content is controlled at 0.28-0.6wt%. Mn has three main functions in the high-strength and tough heatless aluminum alloy of the present invention. One is to dissolve impure iron to form (Fe, Mn)Al 6 , reduce the harmful effects of iron, secondly, prevent mold sticking and increase mold life, thirdly, as a strengthening element, it forms MnAl with aluminum 6 In the high-strength and tough heatless aluminum alloy of the present invention, the M value (the total mass percentage of Mn+Fe) must be strictly controlled within the range of 0.6%-0.8%.

[0017] Fe is a non-main alloying element in the heatless aluminum alloy of the present invention, and its content is controlled at 0.08-0.50wt%. The main function of Fe in the high-strength and tough heatless aluminum alloy of the present invention is to prevent mold sticking and improve mold life. The Fe content range directly determines which recycled scrap aluminum can be selected and which scrap aluminum cannot be selected during the actual production of aluminum alloy ingots, thus directly determining the final material cost and carbon reduction ratio. Considering that the Fe-containing phase has a greater negative impact on the toughness of the alloy, the design of the entire alloy system revolves around reducing the negative impact of the iron-rich phase on the toughness of the alloy. As the first aspect of the main innovation of the patent of the present invention, the regulation of the iron-rich phase is achieved by controlling the M value (the total mass percentage of Mn+Fe).

[0018] In the die-cast aluminum alloy of the present invention, the combined addition of microalloying elements lanthanum La and yttrium Y has two main effects: one is to effectively modify the primary iron-rich phase, and the other is to improve the long-term thermal stability volatility of the alloy. This is the second main innovation of the present invention. The inventors have found through a large number of experiments that when the rare earth elements La and Y are added together, and the La / Y ratio (N value) is controlled to be 1.8-2.2, the primary iron-rich phase can be effectively modified, thereby minimizing the impact of the iron-rich phase on the toughness of the alloy. At the same time, the inventors also found that when the rare earth elements La and Y are added together, and the La / Y ratio (N value) is controlled to be 1.8-2.2, it has a significant effect on improving the thermal stability of the alloy. In the long-term thermal stability volatility test at 150°C and 1000 hours, the long-term thermal stability volatility of the embodiment of the present invention is significantly reduced compared with the comparative example. In the high-strength and toughness die-casting aluminum alloy of the present invention, the control range of lanthanum is 0.01-0.03wt%, the control range of yttrium is 0.005-0.015wt%, and the control range of N value (La / Y ratio) is 1.8-2.2.

[0019] Secondly, the rare earth elements La and Y play a role in purifying the alloy melt. On the one hand, rare earth has a great affinity with hydrogen, can absorb and dissolve hydrogen in large quantities, and form stable compounds of LaH and YH, which will not gather into bubbles and be removed in the form of aluminum slag, improving the pinhole rate of the alloy; on the other hand, rare earth elements La and Y will form refractory compounds with oxygen and nitrogen. The ABB company's prefil-foorprinter aluminum slag detector is used to perform qualitative and quantitative analysis of aluminum slag, reduce oxide inclusions in the alloy, improve the purity of the alloy melt, and improve the fatigue performance of the alloy. The K value (La+2Y) is controlled at 0.035-0.05. If the K value is lower than 0.035, the rare earth element content is low and the melt cannot be purified; if the K value is higher than 0.05, the purification effect is not significantly improved, and the alloy cost is increased. The K value is preferably in the range of 0.035-0.05, and an excellent purification effect is achieved at the lowest addition amount.

[0020] Sr is a microalloying element in the die-casting aluminum alloy of the present invention, and its content is controlled at 0.08-0.2wt%. The main function of Sr in the high-strength and toughness die-casting aluminum alloy of the present invention is to modify the eutectic Si phase and the Fe-containing phase. In the present invention, considering the modification effect of the Fe-containing phase, during the preparation process of the high-strength and toughness die-casting aluminum alloy, Sr is added twice, the first addition is added in the form of AlSr10 master alloy, and the second addition is added in the form of AlSr10Ti5C combined with a refining modifier, and the total content range is controlled to be 0.01-0.03wt%.

[0021] Zn is controlled as an impurity element in the heatless aluminum alloy of the present invention, and its content is ≤0.6wt%. The upper limit of the content range of Zn as an impurity element in the high-strength and tough heatless aluminum alloy of the present invention is significantly higher than that of other impurity elements, mainly because: 1) within this content range, Zn element has no significant effect on the strength and toughness of the alloy; 2) in the actual aluminum ingot production, the selection range of recycled aluminum can be significantly increased, which is conducive to reducing material costs.

[0022] Another aspect of the present invention provides a method for preparing the above-mentioned high-strength, light-weight, heat-treatment-free die-casting aluminum alloy for large and complex structural parts, comprising the following steps:

[0023] (1) preparing raw and auxiliary materials in accordance with the mass ratio, including: aluminum ingots for remelting, industrial silicon, pure magnesium ingots, 80% iron agent, AlMn10 master alloy, AlSr10 master alloy, AlTi10 master alloy, AlLa10 master alloy, AlY10 master alloy, AlSr10Ti5C combined refining modifier;

[0024] (2) placing aluminum ingots for remelting, industrial silicon, 80% iron agent, AlMn10 master alloy, AlTi10 master alloy, AlLa10 master alloy, AlY10 master alloy, and AlZr10 master alloy in a proportion in an aluminum melting furnace, controlling the furnace temperature at 760-770° C. and heating until fully melted to obtain a first alloy liquid;

[0025] (3) The temperature of the first alloy liquid is controlled at 700-720° C., and pure magnesium ingot and AlSr10 master alloy are added to the first alloy liquid in proportion to obtain a second alloy liquid;

[0026] (4) the temperature of the second alloy liquid is controlled at 700-710° C., and 0.1-0.3% of AlSr10Ti5C combined refining modifier is added to obtain a third alloy liquid;

[0027] 5) The temperature of the third alloy liquid is controlled at 680-700°C, and online degassing, slag removal, filtering and casting are carried out to obtain a heat-free die-casting aluminum alloy.

[0028] Furthermore, in step (4), the AlSr10Ti5C combined refining modifier is the combined refining modifier disclosed in CN108384972A, purchased from Lizhong Sitong Light Alloy Group Co., Ltd., with the model number of AlSr10Ti5C and the name of combined refining modifier.

[0029] Furthermore, in step (5), during the slag removal, 3 wt‰ refining agent is added for purification.

[0030] Furthermore, in step (5), the refining agent adopts the refining agent disclosed in CN109306412A, wherein the content of Na element in the refining agent is 15-35wt%, the content of K element is 5-10wt%, the content of Si element is 1-5wt%, the content of Cl element is 20-50wt%, the content of F is 8-15wt%, the content of Al element is ≤5wt%, the content of C element is ≤5wt%; the content of Ca is ≤5wt%, and the content of Mg element is 3-10wt%.

[0031] Furthermore, in step (5), the degassing is furnace degassing; during the furnace degassing, the furnace temperature is adjusted to 680-700°C, and argon gas is used for furnace degassing.

[0032] Furthermore, in step (5), the outlet pressure of the argon gas for degassing in the furnace is 0.4-0.6Mpa, and the degassing time is not less than 40min. Furthermore, the speed of the degasser for online degassing is 400-450rpm, and the argon gas flow rate is 15-25LPM; before online degassing, the degassing box is preheated at a temperature of 350-400°C.

[0033] In terms of raw material selection, the heat-free aluminum alloy of the present invention has higher upper limits of Fe, Zn, and Cu elements compared with Alcoa C611 and other heat-free alloys, so a higher proportion of recycled aluminum can be selected in terms of raw material selection; compared with Rhinefield castsail-37 and other heat-free alloys, no more expensive alloying elements such as Mo and V are added and the upper limit value is higher. Considering the above two points, the heat-free aluminum alloy of the present invention has obvious cost advantages and carbon reduction advantages while ensuring the performance.

[0034] In terms of modification and refinement, the main innovation of the present invention is that, in view of the high requirements for material toughness of high-strength and lightweight large structural parts and the characteristics of aluminum-silicon cast aluminum alloys, the traditional aluminum-titanium-boron grain refiner is not used, but the material is modified with traditional aluminum-strontium and then AlSr10Ti5C combined refinement modifier is added. A large number of test results show that the addition of AlSr10Ti5C combined refinement modifier can effectively refine the grains while further strengthening the modification.

[0035] In terms of purification treatment, the present invention ensures that the aluminum liquid has a high purity by efficiently removing non-metallic inclusions, oxides and gas in the aluminum liquid, thereby avoiding the production of defective products in the later stage due to poor purification effect of the gas content in the aluminum liquid.

[0036] Advantages and beneficial effects of the present invention:

[0037] (1) The present invention significantly reduces the long-term thermal stability fluctuation rate of the heat-treatment-free die-cast aluminum alloy by controlling the element ratio, especially controlling the total mass percentage of Mn+Fe to 0.6%-0.75%, the rare earth element La / Y ratio to 1.8-2.2, and the total mass percentage of La+2Y to 0.035%-0.055%. In the long-term thermal stability test of 150℃*1000h, the long-term thermal stability fluctuation rate is not higher than 35%.

[0038] (2) The selection range of recycled scrap aluminum for the heat-treatment-free die-casting aluminum alloy of the present invention is greatly widened, and the proportion of recycled aluminum added can be significantly increased. Moreover, under the condition of a high proportion of recycled aluminum added, the fatigue strength is not significantly reduced, and the stability of the elongation test data is not significantly reduced. This can not only reduce carbon, but also effectively reduce costs.

[0039] (3) The heat-treatment-free die-cast aluminum alloy of the present invention is mainly used in the production of large-scale automotive structural parts that are large in size, complex in structure, have high requirements for strength and toughness, and are difficult to heat treat. Without the need for heat treatment, it can meet the production needs of high-strength and lightweight automotive structural parts with a tensile strength of 260 to 290 MPa, a yield strength of 130 to 150 MPa, and an elongation after fracture of 11 to 15%. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 This is a real picture of a 3mm vacuum die-casting test piece;

[0041] Figure 2 This is the metallographic structure diagram of the 3 mm vacuum die-casting specimen prepared in Example 5.

[0042] Figure 3 This is the typical microstructure of the quaternary AlSiFeMn phase in the 3 mm vacuum die-cast test piece prepared in Example 5.

[0043] Figure 4 These are the energy spectrum analysis results of the quaternary AlSiFeMn phase in the 3 mm vacuum die-casting specimen prepared in Example 5.

[0044] Figure 5 This is the oxidized slag organization diagram of Example 5.

[0045] Figure 6 This is the oxidized slag organization diagram of Comparative Example 6.

[0046] Figure 7 The typical microstructure of La-rich and Y-phase in the 3 mm vacuum die-casting specimen prepared in Example 5;

[0047] Figure 8 These are the energy spectrum analysis results of the quaternary AlSiFeMnYLaMg phase in the 3 mm vacuum die-casting specimen prepared in Example 5. DETAILED DESCRIPTION

[0048] The present invention is described below with reference to specific embodiments. It should be noted that these embodiments are merely illustrative and do not limit the present invention in any way.

[0049] Example 1

[0050] A heat-treatment-free die-cast aluminum alloy for high-strength, toughness, lightweight, large and complex structural parts, comprising Si: 9.11wt%; Mg: 0.22wt%; Mn: 0.59wt%; Fe: 0.09wt%; Sr: 0.18wt%; Ti: 0.08wt%; La: 0.02wt%; Y: 0.01wt%, Zr: 0.15%, and the balance is Al. The total mass percentage M of Mn+Fe is 0.68wt%, the La / Y ratio N is 2, and the total mass percentage K of La+2Y is 0.04wt%.

[0051] The preparation method is:

[0052] The raw materials and the added proportions are: aluminum ingot Al99.70 for remelting, 83.34wt%; 3303 industrial silicon, 9.11wt%; pure magnesium ingot Mg9995, 0.22wt%; AlMn10 master alloy, 5.9wt%; AlSr10 master alloy, 0.18wt%; AlTi10 master alloy, 0.8wt%; AlLa10 master alloy, 0.2%; AlY10 master alloy, 0.1%; AlZr10 master alloy, 1.5%.

[0053] Aluminum ingots Al99.70, 3303 industrial silicon, iron agent, AlMn10 master alloy, AlTi10 master alloy, AlLa10 master alloy, AlY10 master alloy and AlZr10 master alloy are placed in a melting furnace in proportion for remelting, and the furnace temperature is controlled at 760-770° C. and heated to fully melt to obtain a first alloy liquid; the aluminum liquid temperature is controlled at 720° C., pure magnesium ingots and AlSr10 master alloy are added to the first alloy liquid in proportion to obtain a second alloy liquid; the aluminum liquid temperature is controlled at 710° C., 0.1-0.3% AlSr10Ti5C combined refining modifier (using the combined refining modifier disclosed in CN108384972A) is added to obtain a third alloy liquid; the third alloy liquid is degassed and deslaged online, Filtration to obtain a die-cast aluminum alloy melt, the actual process parameters are: the furnace temperature is controlled at 700°C, 3wt‰ refining agent is added for purification, the refining agent contains 15-35wt% Na, 5-10wt% K, 1-5wt% Si, 20-50wt% Cl, 8-15wt%, ≤5wt% Al, ≤5wt% C; Ca content ≤5wt%, 3-10wt% Mg; the argon outlet pressure of the furnace degassing is 0.5Mpa, and the degassing time is 40min; the degasser speed of the online degassing is 450rpm, and the argon flow rate is 20LPM; before online degassing, the degassing box is preheated at 380°C.

[0054] The die-casting aluminum alloy melt material prepared according to the above method is vacuum die-casted according to the following method and process, and the mechanical properties are tested.

[0055] (1) The die-casting aluminum alloy melt material is added to the aluminum melting furnace of the die-casting machine, the aluminum liquid temperature is controlled at 700-710°C, argon gas is introduced and the melt is continuously stirred for 30 minutes to further remove the gas in the melt; after slagging, it is allowed to stand for 10 minutes, and the aluminum liquid temperature is controlled at 705°C.

[0056] (2) A LK IMPRESS-Ⅲ DCC500 die-casting machine was used for vacuum high-pressure casting. The casting pressure was 1000 bar, the slow shot speed was 0.2 m / s, the fast shot speed was 5 m / s, the mold temperature and the barrel temperature were 180 °C, the mold used was a flat mold with a length of 200 mm and a width of 65 mm, and a wall thickness of 3 mm. The vacuum machine used was an Aigaia HG600 vacuum machine, and the cavity vacuum degree was <50 mbar.

[0057] The mechanical properties of the 3 mm die-casting specimens were tested, and the results are shown in Table 1. The aluminum slag was qualitatively and quantitatively analyzed using the ABB prefil-foorprinter aluminum slag detector. The content of oxide inclusions in the alloy is shown in Table 2.

[0058] Embodiment 2-5

[0059] A series of aluminum alloys were prepared by the same process as in Example 1, and the specific components and contents are shown in Table 1 (the balance is aluminum and inevitable impurities, not shown). The prepared aluminum alloys were vacuum die-casted by the same process as in Example 1, and the mechanical properties and oxidation slag inclusion tests were performed on the 3 mm die-cast test pieces, and the test results are shown in Table 2.

[0060] Example 6

[0061] The raw materials and the addition ratio are: 80% recycled aluminum, 50% of which are waste automobile wheels, 30% are waste A356 steering knuckles, and the rest are 3303 metal silicon, AlTi10 master alloy, AlMn10 master alloy, metal Mg, AlZr5 master alloy, AlLa10 master alloy, and AlY10 master alloy. The composition is adjusted to the qualified composition as shown in Table 1. The obtained aluminum alloy is vacuum die-casted by the same process as in Example 1, and the 3 mm die-cast test piece is subjected to mechanical property tests and oxidation slag inclusion tests. The test results are shown in Table 2.

[0062] Example 7

[0063] The raw materials and the addition ratios are as follows: 90% recycled aluminum, 30% scrap automobile wheels, 30% scrap A356 steering knuckles, 30% 1 series alloys, and the rest 3303 metal silicon, AlTi10 master alloy, AlMn10 master alloy, metal Mg, AlZr5 master alloy, AlLa10 master alloy, and AlY10 master alloy. The composition is adjusted to the qualified composition as shown in Table 1. The obtained aluminum alloy is vacuum die-casted by the same process as in Example 1, and the 3 mm die-cast test piece is subjected to mechanical property tests and oxidation slag inclusion tests. The test results are shown in Table 2.

[0064] Example 8

[0065] The raw materials and the addition ratios are as follows: 95% recycled aluminum, 35% scrap automobile wheels, 30% scrap A356 steering knuckles, 30% 1 series alloys, and the rest 3303 metal silicon, AlTi10 master alloy, AlMn10 master alloy, metal Mg, AlZr5 master alloy, AlLa10 master alloy, and AlY10 master alloy. The composition is adjusted to the qualified composition as shown in Table 1. The obtained aluminum alloy is vacuum die-casted by the same process as in Example 1, and the 3 mm die-cast test piece is subjected to mechanical property tests and oxidation slag inclusion tests. The test results are shown in Table 2.

[0066] Table 1 Element contents of aluminum alloys prepared in Examples 1 to 8 (wt%)

[0067]

[0068]

[0069] Table 2 Different indexes and properties of alloys

[0070]

[0071] Notes: 1. The "standard deviation" data in the table is obtained by statistics of 10 groups of elongation data. 2. Long-term thermal stability fluctuation rate: (yield strength after long-term heat treatment-cast yield strength)% / cast yield strength, long-term heat treatment process is 150℃, 1000 hours.

[0072] In Examples 1-8, the content of each component was changed and the mechanical properties of the prepared aluminum alloy specimens were tested. The results showed that when the content of each component, M value (Mn+Fe), N value (La / Y), and K value (La+2Y) were all within the control range, the tensile strength, yield strength, and elongation after fracture of the prepared aluminum alloy specimens all met the performance requirements of large automotive structural parts.

[0073] Figure 2 This is the metallographic structure diagram of the 3 mm vacuum die-casting test piece prepared in Example 5. Figure 3 The typical microstructure of the quaternary AlSiFeMn phase in the 3 mm vacuum die-casting specimen prepared in Example 5 is shown in FIG. Figure 4 The energy spectrum analysis results of the quaternary AlSiFeMn phase in the 3 mm vacuum die-casting test piece prepared in Example 5 are as follows: Figure 5 This is the metallographic structure diagram of the oxidized slag prepared in Example 5.

[0074] Comparative Example 1

[0075] The only difference from Example 1 is that the Mn content is changed to 0.39wt%, the M value (Mn+Fe) is 0.48, and the other components and contents are shown in Table 3 (the balance is aluminum and inevitable impurities, not shown). The obtained aluminum alloy is vacuum die-casted using the same process as Example 1, and the test piece is tested for mechanical properties and oxidation slag inclusions, and the test results are shown in Table 4. The main difference between the performance of Comparative Example 1 and Example 1 is that the strength is insufficient.

[0076] Comparative Example 2

[0077] The only difference from Example 4 is that La and Y are not added, and the other components and contents are shown in Table 3 (the balance is aluminum and unavoidable impurities, not shown). The obtained aluminum alloy is vacuum die-casted using the same process as Example 4, and the test piece is subjected to mechanical property test and oxidation slag inclusion test, and the test results are shown in Table 4. The main difference between the performance of Comparative Example 2 and Example 4 is that the mean value of elongation after fracture is reduced, especially the data standard deviation of 30 groups of elongation after fracture data is significantly increased, which will cause a significant increase in the performance difference of different parts of large structural parts.

[0078] Comparative Example 3

[0079] The difference from Example 4 is only that the addition ratio of La and Y is different, the N value (La / Y) is 0.5, and the other components and contents are shown in Table 3 (the balance is aluminum and inevitable impurities, not shown). The obtained aluminum alloy is vacuum die-casted using the same process as Example 4, and the test piece is subjected to mechanical property test and oxidation slag test, and the test results are shown in Table 4. The main difference between the performance of Comparative Example 3 and Example 4 is that the mean value of elongation after fracture is reduced, especially the data standard deviation of 30 groups of elongation after fracture data is significantly increased, which will cause a significant increase in the performance difference of different parts of large structural parts.

[0080] Comparative Example 4

[0081] The difference from Example 5 is that the content of Mn is changed to 0.5wt%, the M value (Mn+Fe) is 0.93, and the other components and contents are shown in Table 3 (the balance is aluminum and inevitable impurities, not shown). The obtained aluminum alloy is vacuum die-casted using the same process as Example 1, and the test bar is subjected to mechanical property test and oxidation slag test, and the test results are shown in Table 4. The main difference between the performance of Comparative Example 4 and Example 5 is that the mean value of elongation after fracture is reduced, especially the data standard deviation of 30 groups of elongation after fracture data is significantly increased, which will cause a significant increase in the performance difference of different parts of large structural parts.

[0082] Comparative Example 5

[0083] The only difference from Example 5 is that no AlSr10Ti5C combined refining modifier is added during the preparation of the die-cast aluminum alloy. The obtained aluminum alloy is vacuum die-casted using the same process as Example 5, and the test bars are tested for mechanical properties and oxidation slag inclusions, and the test results are shown in Table 4. The main difference between the performance of Comparative Example 5 and Example 5 is that the data standard deviation of 30 groups of elongation after fracture data is significantly increased, which will cause a significant increase in the performance differences of different parts of large structural parts.

[0084] Comparative Example 6

[0085] The only difference from Example 5 is that La and Y are not added. The other components and their contents are shown in Table 3 (the balance is aluminum and unavoidable impurities, not shown). The obtained aluminum alloy is vacuum die-casted using the same process as Example 5, and the test pieces are subjected to mechanical property tests and oxidation slag tests. The test results are shown in Table 4.

[0086] Comparative Example 7

[0087] The only difference from Example 6 is that La and Y are not added. The other components and contents are shown in Table 3 (the balance is aluminum and unavoidable impurities, not shown). The obtained aluminum alloy is vacuum die-casted using the same process as Example 6, and the test piece is subjected to mechanical property tests and oxidation slag tests, and the test results are shown in Table 4.

[0088] Comparative Example 8

[0089] The only difference from Example 7 is that La and Y are not added. The other components and contents are shown in Table 3 (the balance is aluminum and unavoidable impurities, not shown). The obtained aluminum alloy is vacuum die-casted using the same process as Example 6, and the test piece is subjected to mechanical property tests and oxidation slag tests, and the test results are shown in Table 4.

[0090] Comparative Example 9

[0091] The only difference from Example 4 is that Y is not added. The other components and their contents are shown in Table 3 (the balance is aluminum and unavoidable impurities, not shown). The obtained aluminum alloy is vacuum die-casted using the same process as Example 4, and the test pieces are subjected to mechanical property tests and oxidation slag tests. The test results are shown in Table 4.

[0092] Comparative Example 10

[0093] The only difference from Example 4 is that La is not added. The other components and their contents are shown in Table 3 (the balance is aluminum and unavoidable impurities, not shown). The obtained aluminum alloy is vacuum die-casted using the same process as Example 4, and the test pieces are subjected to mechanical property tests and oxidation slag tests. The test results are shown in Table 4.

[0094] Comparative Example 11

[0095] The only difference from Example 4 is that the lanthanum / yttrium ratio (La / Y) N is 2.5, lanthanum is 0.025wt%, yttrium is 0.01wt%, and other components and their contents are shown in Table 3 (the balance is aluminum and unavoidable impurities, not shown). The obtained aluminum alloy is vacuum die-casted using the same process as Example 4, and the test pieces are subjected to mechanical property tests and oxidation slag tests. The test results are shown in Table 4.

[0096] Comparative Example 12

[0097] The only difference from Example 4 is that the value K of La+2Y is 0.051wt%, lanthanum is 0.026wt%, yttrium is 0.0125wt%, and other components and their contents are shown in Table 3 (the balance is aluminum and inevitable impurities, not shown). The obtained aluminum alloy is vacuum die-casted using the same process as Example 4, and the test pieces are subjected to mechanical property tests and oxidation slag tests. The test results are shown in Table 4.

[0098] The metallographic structure of the 3 mm vacuum die-casting test piece prepared in Comparative Example 5 is as follows: Figure 6 As shown, the structure diagram of oxide slag is as follows Figure 7 shown.

[0099] Table 3 Element content of aluminum alloy prepared in comparative example (wt%)

[0100]

[0101] Note: The "standard deviation" data in the table is obtained by statistics of 10 sets of elongation data.

[0102] Table 4 Different indexes and properties of alloys in comparative examples

[0103]

[0104] like Figure 7 As shown, the fine La-rich and Y-rich phases (about 2 μm) are dispersed in the matrix, and this high-melting-point refractory phase can pin dislocations under high temperature conditions to enhance the high-temperature strength of the alloy, thereby improving the long-term stability of the alloy.

[0105] According to Comparative Example 6 ( Figure 6 ) and Example 5 ( Figure 5 ) shows that the addition of La and Y can purify the melt and reduce the formation of oxide inclusions in the metallographic phase, thereby improving the comprehensive performance of the alloy.

[0106] According to the data in Table 2 and Table 4, it can be seen that as the content of recycled aluminum increases in Examples 6 to 8, the mechanical properties and fatigue resistance of the alloys remain very stable. In Comparative Examples 7 to 8, La and Y are not added, and the mechanical properties and fatigue resistance of the alloys decrease significantly, because as the proportion of recycled aluminum increases, the slag inclusions in the aluminum melt increase, and these slag inclusions are not co-latticed with the matrix lattice, which easily causes stress concentration to form crack sources, resulting in a decrease in mechanical properties and fatigue resistance. The addition of La and Y elements has a purifying effect on the aluminum melt, reducing the harm of oxidized slag inclusions. At the same time, La and Y elements form fine dispersed stable compounds with Al, improving the toughness and thermal stability of the alloy.

[0107] The above only describes exemplary embodiments or embodiments of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention can be modified and varied in various ways. Any modification, equivalent substitution, improvement, etc. made within the spirit and principle of the present invention are included in the scope of the claims of this application.

Claims

1. A heat-treatment-free die-cast aluminum alloy for high-strength, light-weight, large and complex structural parts, characterized in that: The aluminum alloy comprises, relative to the total weight, 8.5-10.5wt% silicon, 0.10-0.30wt% magnesium, 0.28-0.6wt% manganese, 0.08-0.50wt% iron, 0.04-0.15wt% titanium, 0.08-0.2wt% strontium, 0.1-0.2wt% zirconium, 0.01-0.03wt% lanthanum, 0.005-0.015wt% yttrium, ≤0.054wt% chromium, ≤0.3wt% molybdenum, ≤0.1wt% vanadium, ≤0.6wt% zinc, The rest is aluminum and inevitable trace impurities, wherein the content of a single element of the trace impurities is ≤0.06wt%, and the total amount of the trace impurities is ≤0.15wt%, wherein the total mass percentage M of manganese and iron is 0.6-0.8wt%; the ratio N of lanthanum to yttrium is 1.8-2.2, the total mass percentage K of lanthanum and twice yttrium is 0.035-0.05wt%, and the aluminum alloy has a tensile strength of 260-290MPa, a yield strength of 130-150MPa, and an elongation after fracture of 11-15%.

2. The heat-treatment-free die-casting aluminum alloy for high-strength, light-weight, large and complex structural parts according to claim 1, characterized in that: Relative to the total weight of the aluminum alloy, it contains: 8.6-9.6wt% of silicon, 0.20-0.23wt% of magnesium, 0.28-0.6wt% of manganese, 0.08-0.45wt% of iron, 0.08-0.13wt% of titanium, 0.12-0.2wt% of strontium, 0.1-0.15wt% of zirconium, 0.01-0.03wt% of lanthanum, 0.01-0.015wt% of yttrium, ≤0.054wt% of chromium, ≤0.3wt% of molybdenum, ≤0.1wt% of vanadium, ≤0.6wt% of zinc, and the rest is aluminum and inevitable trace impurities, wherein the content of a single element of the trace impurities is ≤0.06wt%, and the total amount of the trace impurities is ≤0.15wt%, wherein the total mass percentage M of manganese and iron is 0.63-0.74wt%; the ratio N of lanthanum to yttrium is 2.0, and the total mass percentage K of lanthanum and twice yttrium is 0.04wt%.

3. The heat-treatment-free die-casting aluminum alloy for high-strength, light-weight, large and complex structural parts according to claim 1, characterized in that: Relative to the total weight of the aluminum alloy, it contains: silicon 8.87-9.22wt%, magnesium 0.20-0.23wt%, manganese 0.28-0.6wt%, iron 0.09-0.42wt%, titanium 0.08-0.12wt%, strontium 0.16-0.19wt%, zirconium 0.15wt%, lanthanum 0.02wt%, yttrium 0.01wt%, chromium ≤0.054wt%, molybdenum ≤0.3wt%, vanadium ≤0.1wt%, zinc ≤0.6wt%, and the rest is aluminum and inevitable trace impurities, wherein the content of a single element of the trace impurities is ≤0.06wt%, and the total amount of the trace impurities is ≤0.15wt%, wherein the total mass percentage M of manganese and iron is 0.63-0.74wt%; the ratio N of lanthanum to yttrium is 2.0, and the total mass percentage K of lanthanum and twice yttrium is 0.04wt%.

4. A method for preparing a heat-treatment-free die-cast aluminum alloy for high-strength, light-weight, large and complex structural parts according to any one of claims 1 to 3, characterized in that: The following steps are involved: (1) preparing raw and auxiliary materials in accordance with the mass ratio, including: aluminum ingots for remelting, industrial silicon, pure magnesium ingots, 80% iron agent, AlMn10 master alloy, AlSr10 master alloy, AlTi10 master alloy, AlLa10 master alloy, AlY10 master alloy, AlZr10 master alloy, AlSr10Ti5C combined refining modifier; (2) placing aluminum ingots for remelting, industrial silicon, 80% iron agent, AlMn10 master alloy, AlTi10 master alloy, AlLa10 master alloy, AlY10 master alloy, and AlZr10 master alloy in a proportion in an aluminum melting furnace, controlling the furnace temperature at 760-770° C. and heating until fully melted to obtain a first alloy liquid; (3) The temperature of the first alloy liquid is controlled at 700-720° C., and pure magnesium ingot and AlSr10 master alloy are added in proportion to obtain a second alloy liquid; (4) the temperature of the second alloy liquid is controlled at 700-710° C., and 0.1-0.3% of AlSr10Ti5C combined refining modifier is added to obtain a third alloy liquid; (5) The temperature of the third alloy liquid is controlled at 680-700°C, and online degassing, slag removal, filtering and casting are carried out to obtain a heat-treatment-free die-casting aluminum alloy.

5. The preparation method according to claim 4, characterized in that: During the slag removal, 3wt‰ refining agent is added for purification treatment, wherein the refining agent contains 15-35wt% Na, 5-10wt% K, 1-5wt% Si, 20-50wt% Cl, 8-15wt% F, ≤5wt% Al, ≤5wt% C; ≤5wt% Ca, and 3-10wt% Mg.

6. The preparation method according to claim 4, characterized in that: The degassing is furnace degassing, during which the furnace temperature is adjusted to 680-700° C., and argon gas is used for furnace degassing.

7. The preparation method according to claim 4, characterized in that: The outlet pressure of the argon gas for degassing in the furnace is 0.4-0.6Mpa, and the degassing time is not less than 40min.

8. The preparation method according to claim 4, characterized in that: The degasser rotation speed of the online degassing is 400-450rpm, and the argon flow rate is 15-25LPM; before the online degassing, the degassing box is preheated at a temperature of 350-400°C.

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