A heat-treatment-free die-cast aluminum alloy for electric bicycles and a preparation method thereof

Abstract

The invention relates to a heat-treatment-free die-casting aluminum alloy for an electric bicycle and a preparation method thereof. The alloy comprises Si: 7.0wt%-11.0wt%; Mg: 0.8-2.0wt%; Cu: 0.5-1.5wt%; Zn: 2.0-8.0wt%; B: 0.001wt%-0.20wt%; Ti: 0.05-0.2wt%; Mn: 0.1-0.8wt%; Fe: 0.05-0.8wt%; Sr: 0.005-0.5wt%; Zr: <0.1wt%; Cr: <0.1wt%; the sum of the weight percentages of other impurities is controlled below 1.0wt%, and the remainder is Al. Compared with the prior art, the material obtained in the present invention can achieve a tensile strength of 310-380MPa, a yield strength of 200-270MPa, an elongation of 2-5%, and a hardness of 100-120HB without heat treatment. The corresponding caliper product can withstand a jaw pressure of >24.5MPa, which meets the product safety requirements, greatly reduces the production cost, and has huge economic benefits.

Description

Technical Field

[0001] The invention relates to an electric bicycle, and in particular to a heat-treatment-free die-casting aluminum alloy for an electric bicycle and a preparation method thereof. Background Art

[0002] The caliper is one of the main parts of the electric bicycle disc brake. After processing, it is used in conjunction with the brake disc, friction plate, brake bracket, etc. It is the part with the most concentrated stress and the most frequent variable load pressure in the electric bicycle. It is related to the safety performance of the electric bicycle, so its design standards are very strict. At present, the caliper material used for electric bicycles is mainly ZL111 aluminum alloy in T6 state, which is generally produced by gravity casting or low-pressure casting. Compared with the high-pressure die-casting production process, the parts produced by gravity casting and low-pressure casting have a low proportion of defects such as pores and cracks. Therefore, the current process is generally based on gravity casting or low-pressure casting. In order to meet the product performance, the ZL111 material must be subjected to high-temperature and long-term solid solution heat treatment and low-temperature aging process to meet the use requirements. If the material has defects such as pores and shrinkage during the casting or casting process, it is very easy to cause bulging, cracks, deformation and other defects during the subsequent high-temperature heat treatment process, resulting in product scrapping. Therefore, the caliper produced by traditional casting or low-pressure casting process has poor yield and production efficiency, and the overall economic benefits are low.

[0003] Patent CN115505799A introduces a high-strength and toughness gravity casting aluminum alloy, its preparation method and application. The aluminum alloy is characterized in that it contains the following components calculated by mass percentage: Si: 5.0~10.0wt%, Cu: 0.001~0.5wt%, Mg: 0.001~1.0wt%, Zn: 0.001~0.5wt%, Fe: 0.003~0.8wt%, Ti: 0.001~0.5wt%, Cr: 0.001~0.4wt%, Zr: 0.001~0.3wt%, Sr: 0.001~0.055wt%, RE: 0.001~0.55wt%, the sum of other unavoidable impurity elements is not more than 0.3wt%, and the balance is aluminum. The castings described in the patent need to undergo solution treatment + low-temperature aging treatment, with a solution temperature of 500℃~600℃, and after keeping warm for 6-8h, they are placed in water at a temperature of 30℃~100℃ for quenching treatment; the low-temperature aging treatment includes the following steps: the temperature is 170℃~190℃, and maintained for 7~8h. The products described in the patent still cannot avoid the heat treatment process, and rare earth elements need to be added additionally, and the production cost and production efficiency are not ideal. Summary of the invention

[0004] The purpose of the present invention is to overcome the defects of the above-mentioned prior art and to provide a heat-free die-cast aluminum alloy for electric bicycles and a preparation method thereof. Since the material can meet the performance requirements without heat treatment, the material can be formed by high-efficiency high-pressure die-casting to produce electric bicycle caliper products. The overall production efficiency is significantly higher than gravity casting and low-pressure casting. Since the product does not require heat treatment, not only the high-temperature and long-term heat treatment process is eliminated, but also the risks of product bulging, deformation, etc. are avoided, the yield rate is improved, and the performance can still meet the requirements, greatly improving the economic benefits.

[0005] The object of the present invention can be achieved by the following technical scheme: a heat-treatment-free die-cast aluminum alloy for electric bicycles, the alloy comprising Si: 7.0wt%-11.0wt%; Mg: 0.8-2.0wt%; Cu: 0.5-1.5wt%; Zn: 2.0-8.0wt%; B: 0.001wt%-0.20wt%; Ti: 0.05-0.2wt%; Mn: 0.1-0.8wt%; Fe: 0.05-0.8wt%; Sr: 0.005-0.5wt%; Zr: <0.1wt%; Cr: <0.1wt%; the sum of the weight percentages of the remaining impurities is controlled below 1.0wt%, and the remainder is Al.

[0006] Preferably, the alloy includes Si: 9.0wt%-10.2wt%; Mg: 1.0-1.3wt%; Cu: 0.5-1.5wt%; Zn: 5.5-6.5wt%; B: 0.01wt%-0.05wt%; Ti: 0.05-0.15wt%; Mn: 0.4-0.7wt%; Fe: 0.2-0.5wt%; Sr: 0.025-0.1wt%; Zr: <0.1wt%; Cr: <0.1wt%; the sum of the weight percentages of the remaining impurities is controlled below 1.0wt%, and the balance is Al.

[0007] Furthermore, in the alloy, (Mn+Cr) / Fe=0.5-2:1.

[0008] Furthermore, the Zr, Mn, Cr, Ti and B are added in the form of Al-Zr, Al-Mn, Al-Cr and Al-Ti-B amorphous master alloys.

[0009] Furthermore, the amorphous intermediate alloy is obtained by the following method: Al-Ti-B, Al-Sr, Al-Mn, Al-Cr and Al-Zr are treated by gas quenching atomization method to obtain intermediate phase alloy amorphous powder.

[0010] Specifically, the intermediate alloy amorphous powder is obtained by the following method: the gas quenching atomization method is described, Al-Ti-B, Al-Sr, Al-Mn, Al-Cr and Al-Zr intermediate phase alloys are added respectively, the alloy is heated to a molten state of 800-1400°C, an inert gas is used as a protective and cooling medium, and a high-speed gas flow is used to impact the molten liquid flow to form tiny droplets, and the cooling rate reaches 10 3 -10 4 K / s, amorphous alloy powder is formed after rapid cooling, and the air flow pressure is 0.5-4Mpa.

[0011] The present invention also provides a method for preparing a heat-treatment-free die-cast aluminum alloy for an electric bicycle, comprising the following steps:

[0012] 1) Put high-purity aluminum into a heating furnace, heat it to 700°C, completely melt it and keep it warm for 15 minutes;

[0013] 2) Raise the temperature to 780°C and add Fe agent;

[0014] 3) Cool down to 760°C and add Si and Cu elements;

[0015] 4) Cooling to 730° C., adding Al-Zr, Al-Cr, Al-Mn, Al-Sr and Al-Ti-B amorphous master alloys;

[0016] 5) Cool down to 720°C and add pure Mg and pure Zn metal materials;

[0017] 6) After all the raw materials are melted, they are cast to obtain aluminum alloy ingots.

[0018] Furthermore, the aluminum alloy casting is subjected to high pressure die casting to form an electric bicycle caliper, which specifically includes the following steps:

[0019] 1) The aluminum alloy ingot is melted again at 750°C and kept warm, and a protective gas is introduced to isolate it from the air during the warming process;

[0020] 2) The molten alloy obtained in step 1) is pre-filled into the barrel by the die-casting machine punch, and the die-casting mold is pre-maintained at a temperature of 250-350° C. by a mold temperature controller. At the same time, the die-casting mold is equipped with a heat-insulating barrel. During die-casting, the barrel temperature is maintained at 200-250° C. The molten aluminum alloy casting received by the barrel is quickly entered into the die-casting mold at a pressure of 20-40 MPa and an injection speed of 4 m / s for cooling and forming;

[0021] 3) Demolding, taking out the casting by a robot arm to obtain an electric bicycle caliper product.

[0022] The obtained caliper material does not require heat treatment and can reach a tensile strength of 310-380MPa, a yield strength of 200-270MPa, an elongation of 2-5%, and a hardness of 100-120HB in a natural state. The product can withstand a jaw pressure greater than 24.5MPa.

[0023] Compared with the prior art, the present invention has the following advantages:

[0024] 1) The Al-Ti-B, Al-Zr, Al-Sr and other multi-alloys prepared by the gas quenching atomization method of the present invention have amorphous powder particle size of <30um, and the size is small and uniform. The material modification and refinement of the aluminum liquid by adding amorphous powder is more uniform than the traditional addition method. The addition of amorphous powder reduces the defects introduced during the addition, and is not easy to produce slag inclusions or undissolved particle phases, thereby improving the purity of the aluminum liquid. At the same time, due to the characteristics of the amorphous structure of the amorphous powder itself, the crystal structure grown with Al-Ti-B, Al-Zr and the like as nucleation particles is more random, thereby more effectively refining the grains and improving the toughness of the material.

[0025] 2) The present invention adopts a specific ratio of (Mn+Cr) / Fe. The addition of Mn can expand the α-Fe phase area. The Mn atom size is similar to that of Fe, and it is easy to interact with Fe. Its addition will transform the long needle-shaped β-Fe phase into a Chinese character-shaped α-Fe phase, greatly weakening the adverse factors of the long needle-shaped β-Fe phase on the mechanical properties of the alloy and inhibiting the formation of β-Fe. The addition of a trace amount of Cr will also transform the long needle-shaped β-Fe phase in the alloy into a fishbone-shaped α-Fe phase or a mesh-shaped α-Al(Mn,Cr)Si phase. The transformed α-Fe phase will be distributed in the dendrite gap, reducing the adverse effects of the needle-shaped phase and reducing stress concentration. Through the combined modification of Mn and Cr, not only can the die-casting performance be improved and the sticking of the mold be reduced, but also the tolerance of the material to Fe can be improved, the harmful effects of Fe can be eliminated, and the toughness can be guaranteed.

[0026] 3) The present invention improves the performance and hardness of the material by adding certain amounts of Mg, Cu, Zr and Zn. The addition of Zr can form fine Al 3 Zr dispersed intermediate phase, the precipitation phase is uniform and fine, has a strong dislocation pinning effect, and improves the strength of the material. The addition of aging elements Cu, Mg and Zn can form nano-scale and submicron-scale Al 2 Cu、Mg 2 Si and MgZn 2The corresponding GP zone and pre-precipitation phase effectively ensure the strength and hardness of the material, and the excess Zn not only plays a solid solution strengthening effect, but also uses the high solid solubility of excess Zn to produce lattice distortion on the matrix. The distortion promotes the formation of more small-sized Mg-Si and other aging clusters, which is beneficial to the increase in the number of GP zones in the material. At the same time, the presence of excess Zn reduces the activation energy of the precipitation of the Mg-Si pre-aging phase β″, making it easier to precipitate the β″ phase, thereby improving the response speed of material hardening and further improving the strength and hardness of the product. DETAILED DESCRIPTION

[0027] 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.

[0028] Examples 1-6

[0029] A heat-treatment-free die-cast aluminum alloy for electric bicycles includes components in percentages as shown in the following Table 1, with the remainder being aluminum and unavoidable impurities.

[0030] The alloy material includes Si: 7.0wt%-11.0wt%; Mg: 0.8-2.0wt%; Cu: 0.5-1.5wt%; Zn: 2.0-8.0wt%; B: 0.001wt%-0.20wt%; Ti: 0.05-0.2wt%; Mn: 0.1-0.8wt%; Fe: 0.05-0.8wt%; Sr: 0.005-0.5wt%; Zr: <0.1wt%; Cr: <0.1wt%; the sum of the weight percentages of the remaining impurities is controlled below 1.0wt%, and the balance is Al.

[0031] Table 1 is a table showing the content of each element in the aluminum alloy of Examples 1-6 and the composition of the materials obtained therefrom

[0032]

[0033]

[0034] Prepare materials according to Table 1 above, wherein Zr, Mn, Cr, Ti, and B are added in the form of Al-Zr, Al-Mn, Al-Cr, and Al-Ti-B amorphous master alloys, and the mesophase alloy amorphous powder is made of commercially available master alloys as raw materials. Al-Ti-B, Al-Sr, Al-Mn, Al-Cr, and Al-Zr are treated by gas quenching atomization to obtain mesophase alloy amorphous powder, so that Zr, Mn, Cr, Ti, and Sr are uniformly dispersed in aluminum liquid;

[0035] 1) Put high-purity aluminum into a heating furnace, heat it to 700°C, completely melt it and keep it warm for 15 minutes;

[0036] 2) Raise the temperature to 780°C and add Fe agent;

[0037] 3) Cool down to 760°C and add Si and Cu elements;

[0038] 4) Cooling to 730° C., adding Al-Zr, Al-Cr, Al-Mn, Al-Sr and Al-Ti-B amorphous master alloys;

[0039] 5) Cool down to 720°C and add pure Mg and pure Zn metal materials;

[0040] 6) After all the raw materials are melted, they are cast to obtain aluminum alloy ingots.

[0041] The aluminum alloy casting is subjected to high pressure die casting to form an electric bicycle caliper, comprising the following steps:

[0042] 1) The aluminum alloy ingot is melted again at 750°C and kept warm, and a protective gas is introduced to isolate it from the air during the warming process;

[0043] 2) When keeping warm, introduce protective gas to isolate it from the air, and then inject it into the die casting mold;

[0044] 3) The molten alloy obtained in step 1) is pre-filled into the barrel by the die-casting machine punch, and the die-casting mold is pre-maintained at a temperature of 250-350° C. by a mold temperature controller. At the same time, the die-casting mold is equipped with a heat-insulating barrel. During die-casting, the barrel temperature is maintained at 200-250° C. The molten aluminum alloy casting received by the barrel is quickly cooled and formed into the die-casting mold at a pressure of 20-40 MPa and a shot speed of 4 m / s;

[0045] 4) demoulding, taking out the casting by a robotic arm to obtain a caliper product for an electric bicycle;

[0046] The aluminum alloy casting is subjected to high pressure die casting to form a 3 mm thick tensile sheet, comprising the following steps:

[0047] 1) The aluminum alloy ingot is melted again at 750°C and kept warm, and a protective gas is introduced to isolate it from the air during the warming process;

[0048] 2) When keeping warm, introduce protective gas to isolate it from the air, and then inject it into the die casting mold;

[0049] 3) The molten alloy obtained in step 1) is pre-filled into the barrel by the die-casting machine punch, and the die-casting mold is pre-maintained at a temperature of 250-350° C. by a mold temperature controller. At the same time, the die-casting mold is equipped with a heat-insulating barrel. During die-casting, the barrel temperature is maintained at 200-250° C. The molten aluminum alloy casting received by the barrel is quickly cooled and formed into the die-casting mold at a pressure of 20-40 MPa and a shot speed of 4 m / s;

[0050] 4) demoulding, taking out the casting by a robotic arm to obtain a 3 mm thick tensile sheet;

[0051] The tensile sheet does not need to be heat treated, and its tensile strength, yield strength and elongation are tested according to the national standard GB / T 228.1-2010.

[0052] The caliper products do not need to be heat treated, and the hardness and jaw pressure of the caliper products are tested.

[0053] The commercially available ZL111-T6 was used as a comparative example.

[0054] Table 2 is a performance comparison table of Examples 1-6 and ZL111-T6

[0055]

[0056] It can be seen from the above table that the material prepared by the present invention can achieve a tensile strength of 310-380 MPa, a yield strength of 200-270 MPa, an elongation of 2-5%, and a hardness of 100-120 HB without heat treatment, and the product can withstand a jaw pressure of >24.5 MPa.

[0057] The material properties of the corresponding product of the present invention (without heat treatment) are close to those of ZL111-T6, and the strengthening and toughening effect of heat-treated aluminum alloy T6 can be achieved without special heat treatment, which greatly reduces the production cost and has extremely high economic benefits.

Claims

1. A heat-treatment-free die-cast aluminum alloy for electric bicycles, characterized in that: The alloy includes Si: 7.0wt%-11.0wt%; Mg: 0.8-2.0wt%; Cu: 0.5-1.5wt%; Zn: 2.0-8.0wt%; B: 0.001wt%-0.20wt%; Ti: 0.05-0.2wt%; Mn: 0.1-0.8wt%; Fe: 0.05-0.8wt%; Sr: 0.005-0.5wt%; Zr: <0.1wt%; Cr: <0.1wt%; the sum of the weight percentages of the remaining impurities is controlled below 1.0wt%, with the remainder being Al; the Zr, Cr, Mn, Sr, Ti and B are added in the form of Al-Zr, Al-Cr, Al-Mn, Al-Sr and Al-Ti-B amorphous master alloys; The amorphous master alloy is obtained by the following method: Al-Ti-B, Al-Sr, Al-Mn, Al-Cr and Al-Zr are treated by gas quenching atomization method to obtain amorphous intermediate phase alloy powder. The gas quenching atomization method is: Al-Ti-B, Al-Sr, Al-Mn, Al-Cr and Al-Zr intermediate phase alloys are heated to 800-1400°C molten state respectively, inert gas is used as protection and cooling medium, and a high-speed gas flow is used to impact the molten liquid flow to form tiny droplets, and the cooling rate reaches 10 3 -10 4 K / s, amorphous alloy powder is formed after rapid cooling, and the air flow pressure is 0.5-4MPa.

2. The heat-treatment-free die-cast aluminum alloy for electric bicycles according to claim 1, characterized in that: The alloy includes Si: 9.0wt%-10.2wt%; Mg: 1.0-1.3wt%; Cu: 0.5-1.5wt%; Zn: 5.5-6.5wt%; B: 0.01wt%-0.05wt%; Ti: 0.05-0.15wt%; Mn: 0.4-0.7wt%; Fe: 0.2-0.5wt%; Sr: 0.025-0.1wt%; Zr: <0.1wt%; Cr: <0.1wt%; the sum of the weight percentages of the remaining impurities is controlled below 1.0wt%, and the balance is Al.

3. A method for preparing a heat-treatment-free die-cast aluminum alloy for an electric bicycle as claimed in any one of claims 1 to 2, characterized in that: The following steps are involved: 1) Place high-purity aluminum into a heating furnace, heat to 700°C, completely melt and keep warm for 15 minutes; 2) Raise the temperature to 780°C and add Fe agent; 3) Cool down to 760°C and add Si and Cu elements; 4) Cooling to 730° C., adding Al-Zr, Al-Cr, Al-Mn, Al-Sr and Al-Ti-B amorphous master alloys; 5) Cool down to 720°C and add pure Mg and pure Zn metal materials; 6) After all the raw materials are melted, they are cast to obtain aluminum alloy ingots.

4. The method for preparing a heat-treatment-free die-cast aluminum alloy for electric bicycles according to claim 3, characterized in that: The aluminum alloy ingot is subjected to high-pressure die-casting to form an electric bicycle caliper.

5. The method for preparing a heat-treatment-free die-cast aluminum alloy for electric bicycles according to claim 4, characterized in that: The high pressure die casting steps are as follows: 1) The aluminum alloy ingot is melted again at 750°C and kept warm, and a protective gas is introduced to isolate it from the air during the warming process; 2) The molten alloy obtained in step 1) is pre-filled into the barrel by the die-casting machine punch, and the die-casting mold is pre-maintained at a temperature of 250-350° C. by a mold temperature controller. At the same time, the die-casting mold is equipped with a heat-insulating barrel. During die-casting, the barrel temperature is maintained at 200-250° C. The molten aluminum alloy received by the barrel is quickly injected into the die-casting mold at a pressure of 20-40 MPa and an injection speed of 4 m / s to be cooled and formed; 3) demolding to obtain the caliper product for electric bicycle.

6. The method for preparing a heat-treatment-free die-cast aluminum alloy for electric bicycles according to claim 4, characterized in that: The caliper material can achieve a tensile strength of 310-380 MPa, a yield strength of 200-270 MPa, an elongation of 2-5%, and a hardness of 100-120 HB without heat treatment, and the corresponding product can withstand a jaw pressure of more than 24.5 MPa.

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