A rare earth modified heat cracking resistant die-casting aluminum alloy and preparation method thereof

Abstract

The present invention relates to a rare earth modified heat cracking resistant die casting aluminum alloy and a preparation method thereof. The components of the die casting aluminum alloy include: Ce: 0.01-8.17 wt%; La: 0.01-8.13wt%; Ga: 0.001-0.65wt%; Fe: 0.05-1.2wt%; Mn: 0.005-1.5wt%; Cr: 0.005-0.3wt%; Ni: 0.001-0.4wt%; Mg: 0.005-0.31wt%; Si: 0.05-0.5wt%; Zn: 0.009-0.35wt%; Zr: 0.01-0.21wt%; Ti: 0.01-0.25w%; B: 0.001-0.1wt%; the sum of the weight percentages of the remaining impurities is controlled below 0.5wt%, and the remainder is Al; wherein the mass ratio of Mg to Si is 0.1 to 1.73:1. Compared with the prior art, the die-casting aluminum alloy of the present invention has good hot cracking resistance, die casting and brazing properties.

Description

Technical Field

[0001] The invention relates to the technical field of die-casting aluminum alloys, and in particular to a rare earth modified heat cracking resistant die-casting aluminum alloy and a preparation method thereof. Background Art

[0002] In the modern industrial field, aluminum alloy materials are widely used in automobile manufacturing and 3C electronic products due to their lightweight, high strength, corrosion resistance and other characteristics. In particular, with the increasing demand for energy conservation, emission reduction and efficiency improvement, the research and development and application of lightweight and high-performance materials have received attention. Among them, die-cast aluminum alloys are widely used due to their good production efficiency and mechanical properties. However, traditional die-cast aluminum alloys cannot be brazed due to their low melting point and poor brazing performance, which limits the promotion and application of die-cast aluminum alloys.

[0003] In order to solve these problems, the improvement of the brazing property of die-cast aluminum alloys has become more and more important, and more and more companies and universities are involved. However, although the solidus temperature of die-cast aluminum alloys can be increased to meet the brazing process through the adjustment of elements at this stage, some die-casting properties and thermal cracking resistance are sacrificed at the same time, resulting in unqualified product quality, and still unable to meet the needs of some products with high-precision assembly or sealing requirements.

[0004] Patent CN117210725A discloses a brazable low thermal conductivity high pressure die-cast aluminum alloy, the elements of which include: up to 0.5 mass% silicon; preferably up to 0.2 mass% silicon; up to 2 mass% iron, preferably up to 0.5 mass% iron; up to 0.3 mass% copper; up to 0.3 mass% zinc; up to 0.85 mass% manganese; preferably up to 0.35 mass% manganese; up to 0.6 mass% chromium; preferably up to 0.5 mass% chromium; up to 0.9 mass% magnesium; preferably up to 0.8 mass% magnesium; up to 0.15 mass% titanium; up to 1.5 mass% nickel; preferably up to 0.1 mass% nickel; 5 to 15 mass% rare earth; the rare earth is preferably one or more of cerium, lanthanum, and praseodymium; up to 0.5 mass% molybdenum; preferably up to 0.2 mass% molybdenum; and at least two or more of the above elements are contained, with the remainder being Al. In this technology, the Fe content is less than 2.0%, preferably less than 0.5%, the Ni content is less than 1.5, preferably less than 0.1%, the Mn content is less than 0.85%, preferably less than 0.35%, and the Cr content is less than 0.6%. In this technology, Fe is proposed mainly to increase demoulding properties, but it will reduce thermal conductivity, preferably less than 0.5%. The role of Mn and Cr is to reduce electrical and thermal conductivity, refine recrystallized grains, and reduce the harmful effects of Fe. The main purpose of adding Fe, Mn, and Cr in this technology is to focus on the relationship between the thermal conductivity of the product and the amount of element addition. Although its tensile strength can reach 230MPa, the yield strength can reach 115MPa, and the elongation can reach 5.6%, due to the lack of control of elements such as Cu and Mg that have a great influence on thermal cracking, and the overall content of high melting point elements Fe, Ni, and Mn is too high, in the actual die-casting and brazing process, cracks are prone to occur in some thin walls or thick-thin transition areas, and product quality cannot be guaranteed. It is difficult to achieve good process effects and quality assurance in the actual production of complex parts.

[0005] Patent CN116377262A discloses a method for making a high-pressure die-cast aluminum alloy that can be used for brazing, and its elements include: up to 0.5% by weight of silicon; up to 0.5% by weight of iron; up to 0.3% by weight of copper; up to 0.3% by weight of zinc; 0.6-1.5% by weight of manganese; up to 0.2% by weight of chromium; 0.3-1.0% by weight of magnesium; up to 0.05% by weight of titanium; 5.0-12.0% by weight of rare earth; wherein the rare earth: 3*Mn is controlled between 2.0 and 3.8. The addition of Fe forms an Al-Fe eutectic to increase the fluidity of the material, the addition of Mn changes the Fe phase morphology and reduces the sticking phenomenon, the addition of Re improves the strength and refines the grains, and the addition of Mg improves the mechanical properties. As we all know, a small amount of Mn in aluminum alloy can transform long needle-shaped β-Fe into blocky Al (Fe, Mn) phase. This technology has a low Fe content. Excessive Mn will form coarse Mn and affect the fluidity of the material. The addition of Mg will increase the tendency of grain boundary cracking in the alloy at the end of solidification, and the sensitivity to hot cracking will increase significantly. In addition, the performance of products strengthened by Mg fluctuates greatly with different wall thicknesses. These problems are likely to lead to cracking verification of products after pressing and uneven performance. At the same time, since the product needs to go through the brazing process, the Mg content in this technology is as high as 0.3-1.0%. Aluminum alloys with too high Mg content (> 0.35%) are not suitable for brazing using the potassium fluoroaluminate (NOCOLOK) brazing process commonly used in the industry. This is because the brazing flux in the brazing will react with the Mg element at high temperature to cause the brazing flux to deactivate and the brazing effect to be poor. Therefore, this patent cannot be applied to the production of precision parts or conventional brazing process products, and has corresponding limitations.

[0006] Therefore, developing a die-cast aluminum alloy with excellent die-casting properties, thermal cracking resistance and good brazing performance can not only play a role in existing automotive manufacturing fields such as runner plates and heat exchange modules, but also meet the needs of lightweight and high-precision assembly in electronic structural parts in the 3C electronic product field. Summary of the invention

[0007] The purpose of the present invention is to provide a rare earth modified heat crack resistant die-casting aluminum alloy and a preparation method thereof in order to overcome the defects of the above-mentioned prior art. The present invention develops a rare earth modified aluminum alloy with excellent performance in heat crack resistance, brazing performance and die-casting properties through a specific rare earth element modification process to meet the industry's high performance requirements for materials.

[0008] The purpose of the present invention can be achieved by the following technical scheme: a rare earth modified heat cracking resistant die-casting aluminum alloy, the composition of the die-casting aluminum alloy includes: Ce: 0.01-8.17 wt%; La: 0.01-8.13 wt%; Ga: 0.001-0.65 wt%; Fe: 0.05-1.2 wt%; Mn: 0.005-1.5 wt%; Cr: 0.005-0.3 wt%; Ni: 0.001-0.4 wt%; Mg: 0.005-0.31 wt%; Si: 0.05-0.5 wt%; Zn: 0.009-0.35 wt%; Zr: 0.01-0.21 wt%; Ti: 0.01-0.25 w%; B: 0.001-0.1 wt%; the sum of the weight percentages of the remaining impurities is controlled below 0.5 wt%, and the balance is Al;

[0009] The mass ratio of Mg to Si is 0.1~1.73:1.

[0010] Further, the die-cast aluminum alloy comprises a yield strength of at least 50 MPa, an elongation of 15%, and a conductivity of 12-31 Ms / m when in the cast state without heat treatment;

[0011] The die-cast aluminum alloy comprises a yield strength of at least 40 MPa, an elongation of 15%, and a conductivity of 13-32 Ms / m after heat treatment at 600° C. for 30 minutes;

[0012] The die-cast aluminum alloy has a hot cracking tendency factor HTS of less than 5 in a cast state.

[0013] Furthermore, the mass percentage of Ce+La+Ga is 6-12%, that is, the sum of the three rare earth elements in the alloy is 6-12%.

[0014] Furthermore, the mass ratio of Mg to Si is 0.17~1.13:1.

[0015] Furthermore, the alloy structure of the die-cast aluminum alloy includes α-Al and Al-Re eutectic structures;

[0016] The eutectic structure mainly includes α-Al phase, Al 11 Ce3 phase, Al11La3 phase, Mg2Si phase, Al3Zr phase, AlFeNi phase and multi-component Al (Fe, Mn, Cr, Re) phase.

[0017] Furthermore, the composition of the die-casting aluminum alloy includes: Ce: 0.01-8.17 wt%; La: 0.01-8.13wt%; Ga: 0.001-0.65wt%; Fe: 0.07-0.81wt%; Mn: 0.006-1.28wt%; Cr: 0.008-0.21wt%; Ni: 0.001-0.37wt%; Mg: 0.02-0.31wt%; Si: 0.08-0.3wt%; Zn: 0.009-0.2wt%; Zr: 0.01-0.21wt%; Ti: 0.08-0.2w%; B: 0.016-0.036wt%; the sum of the weight percentages of the remaining impurities is controlled below 0.5wt%, and the balance is Al.

[0018] The present invention also provides a method for preparing a rare earth modified heat cracking resistant die-casting aluminum alloy, the method comprising the following steps:

[0019] Step S1: first weigh pure Al raw material, Mg ingot, Zn ingot, Al-Si, Al-Fe, Al-Zr, Al-Ni, Al-Mn, Al-Cr, Al-La, Al-Ce, Al-Ga and Al-Ti-B alloy according to mass ratio;

[0020] Step S2: firstly, pure Al element is put into a heating furnace and heated to 680°C to obtain molten aluminum liquid. After the aluminum liquid metal is completely melted, it is kept at a temperature for 20-30 minutes;

[0021] Step S3: Raise the temperature to 780°C, add Al-Si, Al-Fe, Al-Cr, Al-Mn, Al-Zr, Al-Ni to the aluminum liquid in proportion, and wait for them to be completely dissolved;

[0022] Step S4: Cooling to 750°C, adding Al-Ce, Al-La, Al-Ga, and Al-Ti-B master alloys, and keeping the temperature for 20-30 minutes;

[0023] Step S5: Cooling to 720°C, adding Mg ingots and Zn ingots, keeping the temperature for 15-20 minutes and then performing degassing and refining;

[0024] Step S6: Cast a small sample for component analysis. If the sample is qualified, the melt is sent to a molding device for molding to obtain the rare earth modified thermal cracking resistant die-cast aluminum alloy.

[0025] Furthermore, the molding equipment is a vacuum die-casting machine, and the specific molding steps are: melting the qualified refined melt again at 720-740°C and keeping it warm, introducing protective gas to isolate it from the air during the insulation, and then injecting it into the die-casting mold for die-casting to obtain a rare earth modified heat-cracking resistant die-casting aluminum alloy.

[0026] Furthermore, the solidus of the rare earth modified heat crack resistant die-cast aluminum alloy is higher than 620°C, can withstand high temperature brazing at 580-620°C, and has good brazing properties.

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

[0028] 1) The present invention effectively improves the flux fluidity during the brazing process and the mechanical properties of the material after welding through the designed addition of Si and Zn. The specific effects of the designed addition of Si and Zn are: 1) At present, the commercially available flux is mainly potassium fluoroaluminate (NOCOLOK). The addition of Zn and Si can improve the activity of potassium fluoroaluminate, enhance the mass transfer between the flux and the substrate and the brazing material, and further reduce the tension between the brazing material and the substrate, thereby improving the fluidity of the material. However, since Si significantly reduces the liquidus temperature, it is more appropriate to control it at 0.05-0.5%; 2) Due to the high brazing temperature (>580℃), the precipitated phases in the material matrix after die casting at such a high temperature will all dissolve back into the aluminum matrix, the strengthening effect of the precipitated phase disappears, and the performance decay after welding is very obvious. The present invention considers utilizing the natural aging of Si, Mg and Cu after welding to improve the mechanical properties of the material. In the present invention, the ratio of Si to Mg is controlled at 0.1~1.73:1 to avoid poisoning reaction between excess Mg and flux potassium fluoroaluminate to weaken the protective effect of the flux, thereby ensuring the brazing effect. At the same time, by adding a small amount of Zn, the transformation of the solute cluster GP zone to the pre-precipitation precipitation phase is stimulated, and high-density and uniformly distributed solute clusters are formed during the placement process after brazing. These clusters can serve as the core of the pre-precipitated β" phase and Q phase, thereby improving the distribution density and precipitation rate of the GP zone corresponding to the aging, and effectively avoiding the problem of mechanical property attenuation of the material after brazing.

[0029] 2) The present invention is mainly based on Al-Re eutectic structure, and the added Ce, La and Ga are all low-melting point eutectic rare earths. The combined addition of diversified rare earths effectively reduces the liquidus temperature of the aluminum alloy. The reduction of the liquidus can effectively reduce the pouring temperature, reduce the amount of air intake, purify the aluminum liquid, and reduce the surface tension of the aluminum liquid, thereby improving the fluidity of the aluminum liquid. Excessive rare earths are prone to produce coarse rare earths, which in turn affect the mechanical properties of the material. The eutectic structure formed by too little rare earth has a poor effect on improving the fluidity of the aluminum liquid. Too much rare earth exceeds the multi-eutectic point, resulting in the appearance of large rare earth precipitation phases, which in turn affects the fluidity of the alloy. After repeated verification by the inventors, a narrow solid-liquid phase range and a better die-casting effect can be obtained within the range of 6-12%.

[0030] 3) In order to further reduce mold sticking and improve the die casting properties of the material, Fe is added to the alloy. Due to the existence of the composition gradient, the high Fe component reduces the speed of iron penetration into the aluminum liquid and reduces the degree of metallurgical reaction between the aluminum liquid and the mold steel. Compared with the traditional modification of the Fe phase by Mn and Cr, this innovative application uses the combined supplementary addition of Mn, Ni and Cr to modify and disperse the morphology of the Fe element. Through the deposition of Ni, Mn and Cr on the surface of the Fe phase, the diffusion of Fe atoms is weakened, thereby changing the distribution morphology of the Fe phase and making the Fe phase distributed in a dispersed phase. This distribution of dispersed phases has better fluidity and structural uniformity than the block phase modified by Mn / Cr alone.

[0031] 4) The present invention adds Zr elements by design, and forms dispersed Al3Zr in the aluminum matrix to prevent the growth of grains during brazing, thereby ensuring the mechanical properties after welding. Since Al3Zr is a high-temperature insoluble phase, the precipitated phase still has a low solid solubility at the brazing temperature, and the distribution is dispersed. This distribution can effectively pin the grain boundaries and hinder the growth of grains at high temperatures, thereby effectively reducing the coarsening of the grain structure during brazing, and ensuring the reliability of the mechanical properties of the product after welding. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 Schematic diagram of the thermal cracking specimen of the present invention.

[0033] Figure 2 This is the microstructure of the die-cast aluminum alloy of Example 2 of the present invention (1000 times).

[0034] Figure 3 This is the microstructure of the die-cast aluminum alloy of comparative example 1 of the present invention (1000 times).

[0035] Figure 4 This is the microstructure of the die-cast aluminum alloy of Example 3 of the present invention (1000 times).

[0036] Figure 5 This is the microstructure (1000 times) of the die-cast aluminum alloy of Comparative Example 2 of the present invention.

[0037] Figure 6 This is the microstructure of the die-cast aluminum alloy of Example 7 of the present invention (1000 times). DETAILED DESCRIPTION

[0038] The following is a detailed description of an embodiment of the present invention. This embodiment is implemented on the premise of the technical solution of the present invention, and a detailed implementation method and a specific operation process are given, but the protection scope of the present invention is not limited to the following embodiment.

[0039] The purpose of the present invention can be achieved by the following technical scheme: a rare earth modified heat cracking resistant die-casting aluminum alloy, the alloy comprises: Ce: 0.01-8.17 wt%; La: 0.01-8.13 wt%; Ga: 0.001-0.65 wt%; Fe: 0.05-1.2 wt%; Mn: 0.005-1.5 wt%; Cr: 0.005-0.3 wt%; Ni: 0.001-0.4 wt%; Mg: 0.005-0.31 wt%; Si: 0.05-0.5 wt%; Zn: 0.009-0.35 wt%; Zr: 0.01-0.21 wt%; Ti: 0.01-0.25 w%; B: 0.001-0.1 wt%; the sum of the weight percentages of the remaining impurities is controlled below 0.5 wt%, and the balance is Al.

[0040] The mass ratio of Mg to Si is 0.1~1.73:1.

[0041] The raw materials used in the present invention are all commercially available raw materials in the art, and the equipment or devices used are all conventional equipment or devices.

[0042] Examples 1-8 and Comparative Examples 1-3

[0043] The formulas of various embodiments and comparative examples are shown in Table 1 below:

[0044] Table 1 is the aluminum alloy content of the embodiment and the comparative example

[0045]

[0046] The present invention also provides a method for preparing a rare earth modified heat cracking resistant die-casting aluminum alloy, which specifically comprises:

[0047] Step S1: first weigh commercially available pure Al raw material, Al-20Si alloy, Mg ingot, Zn ingot, Al-20Fe, Al-5Zr, Al-10Ni, Al-15Mn, Al-Cr, Al-20La, Al-20Ce, Al-20Ga and Al-Ti-B alloy according to mass ratio.

[0048] Step S2: firstly, pure Al element is put into a heating furnace, and heated to 680° C. to obtain molten aluminum liquid, and after the aluminum liquid metal is completely melted, it is kept at a temperature for 20-30 minutes;

[0049] Step S3: Raise the temperature to 780°C, add Al-Si, Al-Fe, Al-Cr, Al-Mn, Al-Zr, Al-Ni to the aluminum liquid in proportion, and wait for them to be completely dissolved;

[0050] Step S4: Cooling to 750°C, adding Al-Ce, Al-La, Al-Ga, and Al-Ti-B master alloys, and keeping the temperature for 20-30 minutes;

[0051] Step S5: Cooling to 720°C, adding Mg ingots and Zn ingots, keeping the temperature for 15-20 minutes and then performing degassing and refining;

[0052] Step S6: Cast a small sample for component analysis. If qualified, send the melt into a molding device, melt it again at 740-760°C and keep it warm. During the heat preservation, introduce protective gas to isolate it from the air, and then inject it into a die-casting mold for die-casting to obtain the rare earth modified heat cracking resistant die-casting aluminum alloy.

[0053] Comparative Example 4

[0054] The alloy was prepared using the formula and method of Example 3 of CN117210725A.

[0055] The obtained alloy was tested for performance, and the results are shown in Table 2 below:

[0056] In the example of Table 2, the material state refers to the state of the alloy after high pressure die casting without any heat treatment;

[0057] After welding refers to the test results of heating the sample from room temperature to 610℃ at a heating rate of 3-4℃ / min, keeping it at 610℃ for 15 minutes, and then taking it out and cooling it to room temperature in air;

[0058] Hardness refers to: the Brinell hardness of the sample material;

[0059] HTS: refers to the thermal cracking tendency factor of the sample;

[0060] In the present invention, the testing of mechanical properties, tensile strength, yield strength and elongation is carried out in accordance with the national standard GB / T 228.1-2010; the hardness is carried out in accordance with GB / T231.1-2018; and the conductivity is carried out in accordance with GB / T12966-2022.

[0061] The hot cracking tendency factor evaluation (HTS) is performed and evaluated according to the following process:

[0062] 1) Cast the molten aluminum corresponding to the sample into a special hot crack restraint rod mold;

[0063] 2) Wait for the sample to completely solidify before taking it out;

[0064] 3) After preparing the hot cracking tendency assessment specimen, observe the degree and quantity of hot cracking of the specimen under a low-power optical microscope, and calculate the results statistically. The HTS value in Table 2 is the average value of the hot cracking tendency of 10 mold assessment specimens. The lower the value, the lower the risk of hot cracking of the specimen;

[0065] 4) Thermal cracking tendency assessment specimens such as Figure 1 As shown in the figure, the calculation formula of the hot cracking tendency factor HTS of this method is: HTS=Σ(f crack ×f length ×f location ),in:

[0066] f crack Refers to the degree of cracks, with no cracks as 0, short cracks as 1, long cracks as 2, obvious cracks as 3, and complete breakage as 4;

[0067] f length Refers to the corresponding crack length, the first value is 32, the second value is 16, the third value is 8, and the fourth value is 4;

[0068] f location Refers to the location where the crack occurs, with the root value being 1, the edge value being 2, and the center area value being 3.

[0069] Table 2 Performance of Examples 1-8 and Comparative Examples 1-3

[0070]

[0071] From the specific results analysis of Table 2 above:

[0072] The difference between Example 2 and Comparative Example 1 is that Example 2 controls the rare earth content and increases the Al-Re eutectic content, while the total amount of rare earth in the comparative example is less than 6w.t%. The results show that the die casting process of Example 2 is smooth, there is no die casting sticking phenomenon, and the mechanical properties are significantly higher than those of the comparative example, and the hot cracking tendency factor HTS is also significantly lower than that of the comparative example 1, proving that too little rare earth does not play a role in improving the die casting performance. Figure 2 and Figure 3 Microscopic comparison shows that Example 2 has more eutectic structure, while Comparative Example 1 has less eutectic structure, which is not conducive to improving fluidity, thus causing difficulties in die casting.

[0073] The difference between Example 3 and Comparative Example 2 is that a higher content of Si element is added to Comparative Example 2. The results show that under the conditions of similar tensile and yield strengths as those of Example 3, the elongation rate of Comparative Example 2 is significantly attenuated, and the toughness of the material is weakened. Figure 3 and Figure 4 Microscopic comparison shows that excessive addition of Si will destroy the Al-Re eutectic structure, resulting in coarsening of the structure, structural damage, decreased die-casting fluidity, and significantly decreased elongation of die-casting materials. At the same time, excessive addition of Si will significantly reduce the liquidus line of the material, making it easy to melt locally during brazing, which can be seen from the further reduction in elongation after welding.

[0074] Compared with Example 3, the difference is that a larger content of Mg element is added in Example 3. Example 3 shows that the hot cracking tendency factor HTS of the comparative example is significantly increased, the brittleness of the material is significantly increased, the product is prone to cracking, and is not conducive to improving the die-casting performance.

[0075] It can be seen from Comparative Example 4 that the alloy obtained by adopting the formula and method of Example 3 of CN117210725A has cracking during die casting, a strong tendency to thermal cracking, cracking, low elongation, and bulging after brazing, and the elongation is further deteriorated.

[0076] It can be seen from the above data that the rare earth modified heat crack resistant die-cast aluminum alloys of Examples 1-8 have excellent die-casting properties, heat resistance and good mechanical properties before / after brazing, and are very suitable for the production of automotive cooling module components and 3C high-precision electronic structural parts and other products. The die-cast aluminum alloy of the present invention has good economic benefits and application range for various production enterprises.

[0077] Figure 2 This is the die-cast aluminum alloy microstructure (1000 times) of Example 2 of the present invention. It can be seen from the figure that: the addition of Re within a reasonable range has a certain content of Al-Re eutectic structure, the eutectic structure is relatively evenly distributed, it is easy to feed shrinkage in the later stage of solidification, and the tendency of hot cracking is low. This distribution morphology can effectively improve the die-casting flowability and mechanical properties of the material.

[0078] Figure 3 This is the die-cast aluminum alloy microstructure (1000 times) of comparative example 1 of the present invention. It can be seen from the figure that although the addition of Re in a smaller range has an Al-Re eutectic structure, the overall proportion is small and the distribution is uneven. This distribution form has poor resistance to thermal cracking and poor die-casting performance.

[0079] Figure 4 This is the microstructure of the die-cast aluminum alloy of Example 3 of the present invention (1000 times). It can be seen from the figure that: with the addition of Re within a reasonable range, the eutectic structure is more evenly distributed, and the material shows good die-casting flowability and mechanical properties.

[0080] Figure 5 This is the die-cast aluminum alloy microstructure (1000 times) of Comparative Example 2 of the present invention. It can be seen from the figure that the addition of excessive Si causes the Al-Re eutectic structure to coarsen, which will reduce the die-casting fluidity of the product, and the mechanical properties show a decrease in elongation.

[0081] Figure 6 This is the microstructure of the die-cast aluminum alloy of Example 7 of the present invention (1000 times), as can be seen from the figure:

[0082] Through the modification effect of mixed rare earth in a reasonable range and the combined effect of Ni, Mn and Cr, the eutectic structure is evenly distributed and the precipitated phase is dispersed. The material shows excellent thermal cracking resistance, die casting performance and brazing / post-welding mechanical properties.

[0083] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the invention patent should be included in the protection scope of the invention patent.

Claims

1. A rare earth modified heat cracking resistant die casting aluminum alloy, characterized in that: The composition of the die-casting aluminum alloy includes: Ce: 0.01-8.17 wt%; La: 0.01-8.13 wt%; Ga: 0.001-0.65 wt%; Fe: 0.07-0.81 wt%; Mn: 0.005-1.28 wt%; Cr: 0.008-0.21 wt%; Ni: 0.001-0.4 wt%; Mg: 0.02-0.31 wt%; Si: 0.08-0.3 wt%; Zn: 0.009-0.2 wt%; Zr: 0.01-0.21 wt%; Ti: 0.08-0.18 w%; B: 0.001-0.1 wt%; the sum of the weight percentages of the remaining impurities is controlled to be below 0.5 wt%, and the balance is Al; The mass ratio of Mg to Si is 0.1~1.73:1; the mass percentage of Ce+La+Ga is 6~12%; The die-cast aluminum alloy has a yield strength of at least 50 MPa, an elongation of 15%, and a conductivity of 12-31 MS / m when in the cast state without heat treatment; The die-cast aluminum alloy comprises a yield strength of at least 40 MPa, an elongation of 15%, and a conductivity of 13-32 MS / m after heat treatment at 600° C. for 30 minutes; The hot cracking tendency factor HTS of the die-cast aluminum alloy in the casting state is less than 5; The alloy structure of the die-cast aluminum alloy includes α-Al and Al-Re eutectic structures; The eutectic structure mainly includes α-Al phase, Al 11 Ce3 phase, Al11La3 phase, Mg2Si phase, Al3Zr phase, AlFeNi phase and multi-component Al (Fe, Mn, Cr, Re) phase.

2. The rare earth modified heat cracking resistant die casting aluminum alloy according to claim 1, wherein The characteristic is that the mass ratio of Mg to Si is 0.17~1.13:

1.

3. The rare earth modified thermal cracking resistant die casting aluminum alloy according to claim 1, characterized in that: The composition of the die-casting aluminum alloy includes: Ce: 0.01-8.17 wt%; La: 0.01-8.13wt%; Ga: 0.001-0.65wt%; Fe: 0.07-0.81wt%; Mn: 0.006-1.28wt%; Cr: 0.008-0.21wt%; Ni: 0.001-0.37wt%; Mg: 0.02-0.31wt%; Si: 0.08-0.3wt%; Zn: 0.009-0.2wt%; Zr: 0.01-0.21wt%; Ti: 0.08-0.11w%; B: 0.016-0.036wt%; the sum of the weight percentages of the remaining impurities is controlled below 0.5wt%, and the balance is Al.

4. A method for preparing a rare earth modified heat cracking resistant die casting aluminum alloy as claimed in any one of claims 1 to 3, characterized in that: The method comprises the following steps: Step S1: first weigh pure Al raw material, Mg ingot, Zn ingot, Al-Si, Al-Fe, Al-Zr, Al-Ni, Al-Mn, Al-Cr, Al-La, Al-Ce, Al-Ga and Al-Ti-B alloy according to mass ratio; Step S2: Firstly, pure Al raw material is put into a heating furnace and heated to 680°C to obtain molten aluminum liquid. After the aluminum liquid metal is completely melted, it is kept at a temperature for 20-30 minutes; Step S3: Raise the temperature to 780°C, add Al-Si, Al-Fe, Al-Cr, Al-Mn, Al-Zr, Al-Ni to the aluminum liquid in proportion, and wait for them to be completely dissolved; Step S4: Cooling to 750°C, adding Al-Ce, Al-La, Al-Ga, and Al-Ti-B master alloys, and keeping the temperature for 20-30 minutes; Step S5: Cooling to 720°C, adding Mg ingots and Zn ingots, keeping the temperature for 15-20 minutes and then performing degassing and refining; Step S6: Cast a small sample for component analysis. If the sample is qualified, the melt is sent to a molding device for molding to obtain the rare earth modified thermal cracking resistant die-cast aluminum alloy.

5. The method for preparing a rare earth modified thermal cracking resistant die-casting aluminum alloy according to claim 4, characterized in that: The molding equipment is a vacuum die-casting machine, and the specific molding steps are: melting the qualified refined melt again at 720-740°C and keeping it warm, introducing protective gas to isolate it from the air during the insulation, and then injecting it into the die-casting mold for die-casting to obtain a rare earth modified heat cracking resistant die-casting aluminum alloy.

6. The method for preparing a rare earth modified heat cracking resistant die casting aluminum alloy according to claim 4, characterized in that: The rare earth modified heat cracking resistant die-casting aluminum alloy has a solidus line higher than 620° C., can withstand high-temperature brazing at 580-620° C., and has good brazing properties.

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