A non-heat-treated high-strength and toughness die-casting aluminum alloy for new energy vehicles and a preparation method thereof

Abstract

The present invention relates to a non-heat-treated high-strength and toughness die-casting aluminum alloy for new energy vehicles and a preparation method thereof. The alloy comprises Si: 8wt%-11wt%; Mg<0.5wt%; Cu<2.0wt%; Zn<1.0wt%; Ti<0.2wt%; B<0.005wt%; Sr<0.1wt%; Ce<0.5wt%; V<0.5wt%; Zr<0.5wt%; Sc<0.05wt%; Fe<1.0wt%; Mn<1.0wt%; the sum of the weight percentages of other impurities is controlled below 1.0wt%, and the balance is Al. Amorphous powders of Al‑Ti‑C‑B, Al‑Sr, Al‑Ce, Al‑Sc and Al‑Zr master alloys were prepared by belt spinning combined with high-energy ball milling. Al‑Ti‑C‑B, Al‑Sr and Al‑Ce were added as refiners and modifiers to significantly improve the elongation of the material. A variety of second phases MnAl6, Al2Cu, Al3Sc and Al3(Sc) were introduced by Cu, Mn, Sc and Zr. 1‑x Zr x ), together with Mg2Si and eutectic Si, effectively improve the strength of the material, making its tensile strength greater than 300MPa, yield strength greater than 120MPa, and elongation 10-14%.

Description

Technical Field

[0001] The present invention relates to an aluminum alloy, and in particular to a non-heat-treated high-strength and toughness die-casting aluminum alloy for new energy vehicles and a preparation method thereof Background Art

[0002] The density of aluminum alloy is about 1 / 3 of that of steel, and it is the most widely used lightweight material in automobiles. Studies have shown that replacing low-carbon steel, cast iron or high-strength steel with aluminum alloy can achieve a weight reduction effect of 30% to 60%, and each kilogram of aluminum alloy can reduce greenhouse gas emissions by 13 to 20 kg. Replacing steel with aluminum is a development trend in automobile lightweight technology.

[0003] If the weight of the vehicle is reduced by 10%, electric vehicles can save 4%-5% of electricity and the cruising range will also be improved. The reduction in vehicle weight can also shorten the braking distance of the vehicle, and at the same time reduce the noise and vibration of the vehicle. Lightweighting is an urgent requirement for the development of new energy vehicles. Due to the configuration requirements of electrification and intelligence, new energy vehicles have added three-electric systems and a large number of intelligent equipment, which has increased weight compared to traditional vehicles. For new energy vehicles, the weight of the battery in the vehicle body accounts for a large part of the overall weight. However, if the battery is too small, the cruising range of new energy vehicles cannot be guaranteed. Therefore, major new energy vehicle manufacturers have spent a lot of effort on lightweighting the vehicle body, especially the lightweighting of the battery. After all, it is the reduction in battery weight that can make the cruising range of new energy vehicles longer. Since new energy vehicle users are sensitive to cruising range and charging time, the lightweight design of new energy vehicles is particularly necessary.

[0004] In the research and development of high-performance die-casting aluminum alloy materials for automotive structural parts, Germany's Rheinfelden is in a leading position. They have developed three different aluminum alloy materials (Silafont36, Castasil37, Magsimal59) for different requirements of automotive structural parts. At present, most aluminum alloy automotive structural parts use these three materials. Among them, Silafont36 and Castasil37 alloys are Al-Si alloys, and their Si content is close to the eutectic point, with very good casting performance. Unlike Castasil37 alloy, Mg element is added to Silafont36 alloy, which improves the strength of the alloy by generating Mg2Si phase with Si. This is also the reason why the Si content of this alloy is higher than that of Castasil37 alloy. However, the Mg content must be controlled (not exceeding 0.5%). Excessive Mg content will increase the number of Mg2Si phases in the alloy, improve the alloy strength, but will cause a sharp drop in elongation. Normally, Silafont36 alloy needs to undergo T7 heat treatment to adjust the strength and plasticity to an acceptable range (yield strength = 150 MPa, elongation = 17%). Magsimal59 alloy is an Al-Mg alloy. All the added Si elements react with Mg to form Mg2Si phase. There is no blocky elemental Si and no need for metamorphic treatment. Moreover, the alloy does not require heat treatment and can have high strength and plasticity (yield strength = 170 MPa, elongation = 10%) at the same time. It can be used directly in the cast state, but the castability of this alloy is lower than that of Al-Si alloy.

[0005] Since traditional commercial die-cast aluminum alloys generally sacrifice toughness to obtain higher strength, they cannot meet the requirements of automotive structural parts for high toughness of alloys. In view of the urgent demand for high-strength and toughness aluminum alloy die-cast structural parts for lightweight automobiles and the fact that large die-cast parts cannot be heat-treated, a high-performance die-cast aluminum alloy material that does not require heat treatment has been developed. Its strength, toughness and die-casting properties can meet the requirements of structural parts such as automotive shock towers and can be used directly in the cast state.

[0006] Chinese patent application 202010605109.3 discloses a high-strength and high-toughness die-cast aluminum alloy material and a preparation method thereof, the alloy including Si: 3wt%-6wt%; Mg: 1.5wt%-3.0wt%; Mn: 0.2wt%-1.8wt%; Cu<2.5%; Fe<0.5wt%; Ti: 0.01wt%-0.2wt%; Sr: 0.005wt%-0.1wt%; Zn<1.0wt%; Y<0.8wt%; Ce<0.5wt%; the sum of the weight percentages of the remaining impurities is controlled below 1.0wt%, and the remainder is Al. Among them, Al-Ti, Al-Y, Al-Ce and Al-Sr master alloy nanopowders are prepared by direct current arc plasma method as raw materials for addition. Compared with the prior art, the silicon content of the aluminum alloy of the present invention is greatly improved, the fluidity and casting performance of the aluminum liquid are significantly improved, and the elongation is significantly improved, which is more suitable for large automobile parts, such as shock towers, front and rear axles, and front and rear longitudinal beams, etc., which are die-casted on die-casting machines above 4000T. However, it is not suitable for use in new energy vehicles, because the product obtained by the formula under the action of its preparation method has high hydrogen content and pinhole degree, and low elongation. Summary of the invention

[0007] The purpose of the present invention is to overcome the defects of the above-mentioned prior art and provide a non-heat-treated high-strength and toughness die-cast aluminum alloy for new energy vehicles and a preparation method thereof. The tensile strength of the tensile sheet sample is greater than 300MPa, the yield strength is greater than 120MPa, and the elongation is 10-14%.

[0008] The object of the present invention can be achieved by the following technical scheme: a non-heat-treated high-strength and toughness die-cast aluminum alloy for new energy vehicles, the alloy comprising Si: 8wt%-11wt%; 0.1≤Mg<0.5wt%; 0.1≤Cu<2.0wt%; 0.4≤Zn<1.0wt%; 0.01≤Ti<0.2wt%; 0.001≤B<0.005wt%; 0.013≤Sr<0.1wt%; 0.12≤Ce<0.5wt%; 0.12≤V<0.5wt%; 0.12≤Zr<0.5wt%; 0≤Sc<0.05wt%; 0.12≤Fe<1.0wt%; 0.05≤Mn<1.0wt%; the sum of the weight percentages of the remaining impurities is controlled below 1.0wt%, and the balance is Al.

[0009] The Ti, C, B, Sr, Ce, Sc and Zr are added in the form of intermediate phase alloys, and Al-Ti-CB, Al-Sr, Al-Ce, Al-Sc and Al-Zr intermediate alloys are used. The intermediate alloy is an intermediate alloy amorphous powder with an average particle size of less than 50nm.

[0010] The intermediate alloy amorphous powder is obtained by the following method: the smelted master alloy is crushed into blocks of appropriate size and loaded into a specially made quartz tube with a small hole at the bottom. The quartz tube is fixed in a vacuum chamber, the top of the quartz tube is connected to the pneumatic brake system, and the distance between the bottom and the roller is generally 2-3mm. Vacuum to 10 -3 Pa level, fill with hydrogen pressure of 0.2-0.3MPa, adjust the roller speed to 2200-2300r / min. Start the high-frequency induction power supply with a current of 18-20A. After the alloy is completely melted, turn on the injection switch, use the pressure difference to spray the melt on the roller to quickly cool it to form a strip, and use the collection tube to collect the prepared strip sample. Under this working parameter, the thickness of the prepared strip sample is generally about 24-30μm and the width is about 2mm. Put the strip sample prepared by the belt into a stainless steel ball mill in a glove box filled with argon gas at a ratio of 30:1 between stainless steel balls and strip samples. After ball milling at a speed of 2500-4000rpm for 48 hours, take out the powder in the glove box to obtain Al-Ti-CB, Al-Sr, Al-Ce, Al-Sc and Al-Zr intermediate alloy amorphous powders with an average particle size of less than 50nm. After adding aluminum liquid to such intermediate alloy amorphous powder during smelting, the content of the added alloying elements can be more accurately controlled, so that the alloying elements can be dispersed more evenly and quickly, and the hydrogen content and pinhole degree of the aluminum alloy are less. Among them, TiC, Sr, Ce, Sc and Zr doped with B elements in Al-Ti-CB can more effectively refine the aluminum matrix and silicon modification, and Ce, Sc and Zr introduce a variety of second phases Al4Ce, Al3Sc, Al3(Sc 1-x Zr x ) together with Mg2Si and Al2Cu act as the second phase reinforcement to achieve the strengthening and toughening of the material.

[0011] The present invention also provides a method for preparing a non-heat-treated high-strength and toughness die-casting aluminum alloy for new energy vehicles, comprising the following steps:

[0012] 1) Put high-purity aluminum into a heating furnace, heat it to 680°C, completely melt it and keep it warm for 15 minutes;

[0013] 2) Raise the temperature to 780°C and add Si, Mn, Fe, Zn, Cu and V single elements;

[0014] 3) cooling to 750°C and adding Al-Ti-CB, Al-Sr, Al-Ce, Al-Sc and Al-Zr intermediate phase alloy amorphous powders;

[0015] 4) Cooling to 720°C and adding pure Mg metal material;

[0016] 5) After all the raw materials are melted, they are cast to obtain aluminum alloy castings.

[0017] The aluminum alloy casting obtained in step (5) is melted again at 750° C. and kept warm. During the keeping warm period, a protective gas is introduced to isolate it from the air. Then, the aluminum alloy casting is injected into a die-casting mold and pressed to obtain a 3 mm thick tensile sheet sample.

[0018] The die-casting mold is a mold temperature controller, which keeps the temperature at 250-350°C in advance. At the same time, the die-casting machine is equipped with a heat-insulating barrel. During die-casting, the barrel temperature is maintained at 200-250°C, and the injection speed is 4m / s. The molten aluminum alloy casting is quickly cooled and formed under a pressure of 20-40MPa.

[0019] The tensile strength of the tensile sheet sample is greater than 300MPa, the yield strength is greater than 120MPa, and the elongation is 10-14%.

[0020] Compared with the prior art, the present invention has the following advantages:

[0021] 1) Al-Ti-BC master alloy mainly contains two kinds of nucleation particles: TiB2 particles and TiC particles doped with B. In the master alloy, TiB2 particles and TiC particles are generated at the same time and distributed alternately, the aggregation degree of particles is significantly reduced, and they are evenly distributed on the matrix. TiC particles are doped with a small amount of B element to form TiB2 with good stability. x C y Particles. It can provide more effective nucleation substrates for the nucleation, so that the alloy can be efficiently refined. Therefore, the master alloy has a good refinement effect and anti-degradation property on the alloy. In addition, the alloy does not contain excessive B elements and will not react with the modified Sr element. Therefore, the addition of Al-Ti-BC master alloy does not affect the modification effect of the modifier on the eutectic silicon in the alloy.

[0022] 2) Ce and Sr form a relatively large supercooling at the front end of the Si phase precipitation, inhibiting the growth of Si, thereby refining the Si phase. At the same time, rare earths hinder the growth of the Si phase and cause multiple twins. The increased twins of the Si phase will cause a significant change in the size of the Si phase, turning the plate-like Si phase into a small short rod-like eutectic phase, thereby achieving a metamorphic effect on the Si phase and improving the elongation of the aluminum alloy.

[0023] 3) Sc and Zr are added to the alloy, Sc has a strong grain refinement effect, and at the same time, a large number of dispersed and coherent secondary Al3Sc and Al3(Sc 1-x Zr x ) phase particles strongly pin dislocations and subgrain boundaries, resulting in strong substructure strengthening. It itself has an extremely strong direct precipitation strengthening effect on the alloy. This strengthening effect is due to the fact that the dispersed and fine second phase particles strongly pin dislocations to hinder the movement of dislocations, greatly increasing the shear stress required for dislocation slip, thereby causing the strengthening of the alloy.

[0024] 4) Compared with the alloy nanopowder prepared by DC arc plasma method, since the plasma method relies on arc discharge evaporation to prepare powder, due to the different boiling points of different metals, the composition of the prepared alloy nanopowder is different from that of the preform. The amorphous alloy powder prepared by the rapid cooling belt spinning method combined with high-energy ball milling completely solves this problem. The composition can be precisely controlled. At the same time, the particle size of the prepared powder is less than 50nm, the alloy element composition is dispersed faster, the amorphous powder contains less hydrogen, and after adding aluminum alloy, the pinhole degree is less, and the defects introduced are less, which helps the material achieve high elongation. DETAILED DESCRIPTION

[0025] 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.

[0026] Examples 1-8

[0027] A non-heat-treated high-strength and toughness die-cast aluminum alloy for new energy vehicles includes the components in the mass percentages described in the following Table 1, with the remainder being aluminum and unavoidable impurities.

[0028] The alloy material includes Si: 8wt%-11wt%; Mg<0.5wt%; Cu<2.0wt%; Zn<1.0wt%; Ti<0.2wt%; B<0.005wt%; Sr<0.1wt%; Ce<0.5wt%; V<0.5wt%; Zr<0.5wt%; Sc<0.05wt%; Fe<1.0wt%; Mn<1.0wt%; the sum of the weight percentages of other impurities is controlled below 1.0wt%, and the balance is Al.

[0029] Table 1 is a table showing the content of each element in the aluminum alloy of Examples 1-8 and the composition of the materials obtained therefrom

[0030]

[0031] The preparation methods of the aluminum alloys described in the above embodiments are as follows:

[0032] 1) Calculate the mass of the required master alloy and prepare the material;

[0033] 2) Place high-purity aluminum into a heating furnace, heat to 600°C, completely melt and keep warm for 15 minutes;

[0034] 3) Raise the temperature to 780°C and add Si, Mn, Fe, Zn, Cu and V single elements;

[0035] 4) cooling to 750°C and adding Al-Ti-CB, Al-Sr, Al-Ce, Al-Sc and Al-Zr intermediate phase alloy amorphous powders;

[0036] 5) Cooling to 720°C and adding pure Mg metal material;

[0037] 6) After all the raw materials are melted, they are cast to obtain aluminum alloy castings. Since the refining agent elements have a certain influence on the strength and elongation of the material, and the materials are all high-purity materials and pre-processed elements, this alloy material is not refined. After the alloy material is cast into an ingot, it is stored for use.

[0038] 7) The aluminum alloy casting is melted again at 750°C and kept warm. The material needs to be isolated from the air during the insulation. Generally, nitrogen is introduced to isolate it from the air during the insulation. Then it is injected into the die-casting mold and a standard tensile sheet with a thickness of 3 mm is obtained by molding. The die-casting mold is a mold temperature controller, which pre-maintains the temperature at 250-350°C. At the same time, the die-casting machine is equipped with a heat-insulating barrel. During die-casting, the barrel temperature is maintained at 200-250°C. The injection speed is 4m / s, and the molten aluminum alloy casting is quickly cooled and formed at a pressure of 20-40MPa. The present invention can more effectively refine the aluminum matrix and silicon metamorphism by doping TiC, Sr, Ce, Sc and Zr with B elements in Al-Ti-CB. Ce, Sc and Zr introduce a variety of second phases Al4Ce, Al3Sc, Al3(Sc 1-x Zr x ) together with Mg2Si and Al2Cu as the second phase reinforcement, the strength of the aluminum alloy is further improved without losing the elongation, thereby realizing the non-heat treatment toughening of the die-cast aluminum alloy. From Table 2, it can be seen that the yield strength of the non-heat treatment high-toughness die-cast aluminum alloy for new energy vehicles is 120-140MPa, the tensile strength is 300-320MPa, and the elongation is 10-14%.

[0039] Table 2 is the mechanical properties of the stretched sheet corresponding to Examples 1-8

[0040]

Claims

1. A non-heat-treated high-strength and toughness die-cast aluminum alloy for new energy vehicles, the alloy consisting of the following components Si: 8wt%-11wt%; 0.1≤Mg<0.5wt%; 0.1≤Cu<2.0wt%; 0.4≤Zn<1.0wt%; 0.01≤Ti<0.2wt%; 0.001≤B<0.005wt%; 0.013≤Sr<0.1wt%; 0.12≤Ce<0.5wt%; 0.12≤V<0.5wt%; 0.12≤Zr<0.5wt%; 0≤Sc<0.05wt%; 0.12≤Fe<1.0wt%; 0.05≤Mn<1.0wt%; the sum of the weight percentages of other impurities is controlled below 1.0wt%, and the balance is Al; The Ti, B, Sr, Ce, Sc and Zr are added in the form of an intermediate phase alloy, using Al-Ti-CB, Al-Sr, Al-Ce, Al-Sc and Al-Zr intermediate alloys, and the intermediate alloy is an intermediate alloy amorphous powder with an average particle size of 30-50nm; The amorphous master alloy powder is obtained by the following method: preparing Al-Ti-CB, Al-Sr, Al-Ce, Al-Sc and Al-Zr master alloy amorphous powders by using a rapid cooling belt spinning method combined with high-energy ball milling; The quenching strip-spinning method adopts a roller speed of 2200-2300 r / min and a hydrogen filling pressure of 0.2-0.3 MPa; The rotation speed of the ball mill of the high-energy ball milling method is as high as 2500-4000 r / min.

2. A method for preparing a non-heat-treated high-strength and toughness die-casting aluminum alloy for new energy vehicles as claimed in claim 1, characterized in that: The following steps are involved: 1) Put high-purity aluminum into a heating furnace, heat it to 680°C, completely melt it and keep it warm for 15 minutes; 2) Raise the temperature to 780°C and add Si, Mn, Fe, Zn, Cu and V single elements; 3) Cooling to 750°C, adding Al-Ti-CB, Al-Sr, Al-Ce, Al-Sc and Al-Zr intermediate phase alloy amorphous powders; 4) Cool down to 720°C and add pure Mg metal material; 5) After all the raw materials are melted, they are cast to obtain aluminum alloy castings.

3. The method for preparing the non-heat-treated high-strength and toughness die-casting aluminum alloy for new energy vehicles according to claim 2, characterized in that: The aluminum alloy casting obtained in step (5) is melted again at 750° C. and kept warm. During the keeping warm period, a protective gas is introduced to isolate the casting from the air. The casting is then injected into a die-casting mold and pressed to obtain a 3 mm thick tensile sheet specimen.

4. The method for preparing the non-heat-treated high-strength and toughness die-casting aluminum alloy for new energy vehicles according to claim 3, characterized in that: The die-casting mold is a mold temperature controller, which pre-maintains the temperature at 250-350°C. At the same time, the die-casting machine is equipped with an insulation barrel. During die-casting, the barrel temperature is maintained at 200-250°C, and the injection speed is 4m / s. The molten aluminum alloy casting is quickly cooled and formed under a pressure of 20-40MPa.

5. The method for preparing the non-heat-treated high-strength and toughness die-casting aluminum alloy for new energy vehicles according to claim 3, characterized in that: The tensile strength of the tensile sheet sample is greater than 300MPa, the yield strength is greater than 120MPa, and the elongation is 10-14%.

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