A lightweight aluminum casting for the front and rear covers of a gearbox and its preparation method

Abstract

The invention discloses a lightweight aluminum casting for a front and rear cover of a gearbox and a preparation method thereof, and relates to the technical field of aluminum castings. In order to improve the performance of the aluminum casting gearbox, the invention limits the raw materials thereof when preparing the aluminum casting, takes aluminum as the main raw material, and adds copper and zinc components therein to improve its casting performance. On this basis, the present application further adds manganese element to the raw materials, and Al and Mn will form an ε-AlMn phase at high temperature, thereby refining the grains in the aluminum alloy, increasing the number of grain boundaries, and improving the strength of the aluminum casting. On this basis, the present application further prepares a composite coating structure, and uses tempering heating to allow diffusion between different coatings, thereby achieving improved bonding between coatings, effectively improving the service life of the aluminum casting coating under thermal cycling, and greatly improving the durability of the aluminum casting gearbox.

Description

Technical Field

[0001] The present invention relates to the technical field of aluminum castings, and specifically to a lightweight aluminum casting for the front and rear covers of a gearbox and a preparation method thereof. Background Art

[0002] The gearbox is a key component in the vehicle power transmission system, responsible for transmitting the power generated by the engine to the wheels through components such as gears and shafts, and adjusting the vehicle speed and torque during this process to achieve better vehicle control;

[0003] Currently, with the implementation of vehicle lightweighting, lightweight aluminum casting gearboxes have become the first choice for gearboxes in the automotive industry. And with various different requirements, improvements to aluminum casting gearboxes are constantly emerging. The use performance of aluminum castings can be improved through surface coatings on aluminum castings. However, since aluminum alloy gearboxes often need to face frequent temperature changes during use, especially in the winter environment in the north of China, the gearbox often needs to be at -20°C and then heat up to 120°C after long-term operation. This often leads to the failure of the surface coating of the aluminum casting, thereby causing a decrease in the wear resistance of the aluminum casting gearbox and affecting its use. Summary of the Invention

[0004] The purpose of the present invention is to provide a lightweight aluminum casting for the front and rear covers of a gearbox and a preparation method thereof to solve the problems raised in the prior art.

[0005] To achieve the above purpose, the present invention provides the following technical solution: A preparation method of a lightweight aluminum casting for the front and rear covers of a gearbox, comprising the following steps:

[0006] S1. Prepare the aluminum casting matrix;

[0007] S11. Melting and die-casting each component to obtain a die-cast blank;

[0008] S12. After cooling the die-cast blank to room temperature, take out the blank, use sandpaper to polish and remove the burrs on the die-cast blank, and then perform shot peening on the surface of the casting to obtain the aluminum casting matrix;

[0009] S2. Prepare the lightweight aluminum casting;

[0010] S21. Place the aluminum casting blank prepared in step S12 in a copper electroplating solution. During electroplating, set the temperature to 55 - 80°C, the current density to 0.5 - 1 A / dm 2 , and the electroplating thickness to 0.5 - 1.5 μm;

[0011] S22. After washing the surface of the aluminum casting blank processed in step S21 with absolute ethanol, under the protection of an argon atmosphere, heat it to 360 - 380 °C, keep it warm for 2 - 3 h, then cool it to room temperature, and place it in a nickel - copper electroplating solution. Control the electroplating temperature at 45 - 50 °C and the current density at 4.5 - 5 A / dm 2 , and the electroplating thickness is 3 - 5 μm;

[0012] S23. After rinsing the surface of the aluminum casting blank processed in step S22 with deionized water, place it in a nickel - chromium electroplating solution. Control the electroplating temperature at 60 - 70 °C and the current density at 1.5 - 2 A / dm 2 , and the electroplating thickness is 0.5 - 1 μm;

[0013] S24. After rinsing the surface of the aluminum casting blank processed in step S23 with deionized water, place it in a chromium electroplating solution again. Control the electroplating temperature at 80 - 90 °C and the current density at 0.5 - 1 A / dm 2 , and the electroplating thickness is 0.2 - 0.7 μm. After the electroplating is completed, rinse and dry the surface of the aluminum casting blank with absolute ethanol. Under an argon atmosphere, heat the aluminum casting blank to 350 - 400 °C, keep it warm for 0.5 - 1 h, then heat it to 550 - 590 °C again, keep it warm for 4 - 8 h, cool it to 350 - 400 °C, keep it warm for 0.5 - 2 h again, then stop heating and cool it in the furnace to room temperature to obtain the lightweight aluminum casting for the front and rear covers of the gearbox.

[0014] Furthermore, by weight percentage, the components of the aluminum casting blank are: Mg 4 - 10%, Si 6.8 - 10%, Mn 1.26 - 2.24%, Cu 5.5 - 8%, Ni 0.5 - 1.8%, Y 0.1 - 0.15%, Zn 5 - 18%, Sc 0.05 - 0.1%, and the balance is Al and unavoidable impurities.

[0015] Furthermore, in step S1, the preparation method of the die - casting blank is as follows:

[0016] After weighing and proportioning each component raw material, under the protection of an argon atmosphere, put it into a melting furnace, heat and melt it to a liquid state, add a refining agent, refine and skim the slag, then place the molten metal in a holding furnace, let it stand for 15 - 30 min, remove the top 15 - 30 mm thick molten metal on the surface of the molten metal, and then die - cast the remaining molten metal. After the die - casting is completed, obtain the die - casting blank.

[0017] Furthermore, in step S11, during die - casting, the temperature of the die - casting mold is 160 - 210 °C and the die - casting speed is 2.5 - 3 m / s.

[0018] Furthermore, in step 21, the copper electroplating solution contains: 150-180 g / L copper sulfate, 40-60 g / L nickel sulfate, 8-15 g / L sodium acetate, 20-30 g / L boric acid, and 0.3-0.8 g / L sodium dodecylbenzene sulfonate.

[0019] Furthermore, in step 22, the nickel-copper electroplating solution contains: 100-200 g / L nickel sulfate, 30-45 g / L copper sulfate, 8-15 g / L sodium acetate, 20-30 g / L boric acid, and 0.3-0.8 g / L sodium dodecylbenzene sulfonate.

[0020] Furthermore, in step 23, the nickel-chromium electroplating solution contains: 40-60 g / L nickel sulfate, 40-60 g / L chromium sulfate, 10-20 g / L sodium acetate, 10-40 g / L sodium sulfite, and 0.5-0.8 g / L sodium dodecyl sulfate.

[0021] Furthermore, in step 24, the chromium electroplating solution contains: 80-120 g / L of chromium sulfate, 10-20 g / L of sodium acetate, 10-40 g / L of sodium sulfite, and 0.5-0.8 g / L of sodium dodecyl sulfate.

[0022] Furthermore, a lightweight aluminum casting for the front and rear covers of a gearbox is prepared by the above method.

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

[0024] In order to improve the performance of the aluminum casting gearbox, the present invention limits the raw materials when preparing the aluminum casting, using aluminum as the main raw material, and adding copper and zinc components therein to improve its casting performance. On this basis, the present application also adds manganese elements to the raw materials. At high temperatures, Al and Mn will form an ε-AlMn phase, thereby refining the grains in the aluminum alloy, increasing the number of grain boundaries, and improving the strength of the aluminum casting;

[0025] And on this basis, the present application further prepares a composite coating structure. When preparing the first coating, since the hardness of the aluminum element itself is relatively low, only 25-35Hv, the present application uses a copper electroplating solution containing more copper and less nickel to prepare the coating. The hardness of copper is approximately between 50-60Hv, which can effectively reduce the stress changes caused by the hardness difference between the coating and the substrate after direct nickel plating, and can effectively improve the bonding performance between the coating and the aluminum substrate. And on this basis, the present application further prepares a multi-layer coating, and in this process is always assisted by tempering heating, so that diffusion can occur between different coatings, thereby achieving an improvement in the bonding strength between the coatings, effectively improving the service life of the aluminum casting coating under thermal cycling, and greatly improving the durability of the aluminum casting gearbox. DETAILED DESCRIPTION

[0026] Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0027] The matrix components of the aluminum casting prepared in this application are as follows: Mg 5.25 - 5.35%, Si 6.14 - 6.16%, Mn 1.24 - 1.26%, Cu 5.5%, Ni 0.55 - 0.56%, Y 0.11 - 0.13%, Zn 10.14 - 10.2%, Sc 0.05 - 0.1%, and the balance is Al and unavoidable impurities.

[0028] Example 1. A method for preparing a lightweight aluminum casting for the front and rear covers of a gearbox, comprising the following steps:

[0029] S1. Prepare the matrix of the aluminum casting;

[0030] S11. After weighing and proportioning the raw material components, under the protection of an argon atmosphere, put them into a melting furnace. After heating and melting to a liquid state, add a refining agent. After refining and skimming the slag, place the molten metal in a holding furnace. After standing for 30 minutes, remove the top 20 mm thick molten metal on the surface of the molten metal, and then die-cast the remaining molten metal. During die-casting, the temperature of the die-casting mold is 200 °C, and the die-casting speed is 2.5 m / s. After die-casting, obtain a die-cast blank;

[0031] S12. After cooling the die-cast blank to room temperature, take out the blank, and use sandpaper to polish and remove the burrs on the die-cast blank, and then perform shot peening on the surface of the casting to obtain the matrix of the aluminum casting;

[0032] S2. Prepare the lightweight aluminum casting;

[0033] S21. Place the aluminum casting blank prepared in step S12 in a copper electroplating solution. During electroplating, set the temperature to 68 °C and the current density to 0.5 A / dm 2 , and the electroplating thickness is 0.5 μm;

[0034] Among them, the copper electroplating solution contains: copper sulfate 150 g / L, nickel sulfate 50 g / L, sodium acetate 8 g / L, boric acid 20 g / L, sodium dodecylbenzenesulfonate 0.5 g / L;

[0035] S22. After washing the surface of the aluminum casting blank treated in step S21 with absolute ethanol, under the protection of an argon atmosphere, heat it to 380 °C, keep it warm for 150 minutes, then cool it to room temperature, and place it in a nickel-copper electroplating solution. Control the electroplating temperature to 45 °C and the current density to 5 A / dm 2 , and the electroplating thickness is 3 μm;

[0036] Among them, the nickel - copper electroplating solution contains: nickel sulfate 130 g / L, copper sulfate 45 g / L, sodium acetate 14 g / L, boric acid 25 g / L, sodium dodecylbenzenesulfonate 0.5 g / L;

[0037] S23. After rinsing the surface of the aluminum casting blank after being treated in step S22 with deionized water, place it in the nickel - chromium electroplating solution, control the electroplating temperature at 60 °C, and the current density at 2 A / dm 2 , and the electroplating thickness is 0.5 μm;

[0038] Among them, the nickel - chromium electroplating solution contains: nickel sulfate 50 g / L, chromium sulfate 50 g / L, sodium acetate 15 g / L, sodium sulfite 30 g / L, sodium dodecyl sulfate 0.8 g / L;

[0039] S24. After rinsing the surface of the aluminum casting blank after being treated in step S23 with deionized water, place it in the chromium electroplating solution again, control the electroplating temperature at 80 °C, and the current density at 1 A / dm 2 , the electroplating thickness is 0.2 μm. After electroplating, rinse the surface of the aluminum casting blank with anhydrous ethanol and dry it. Under an argon atmosphere, heat the aluminum casting blank to 400 °C, keep it warm for 1 h, then heat it to 550 °C again, keep it warm for 4 h, cool it to 370 °C, keep it warm for 1.5 h again, stop heating, and cool it to room temperature with the furnace to obtain the lightweight aluminum casting for the front and rear covers of the gearbox;

[0040] Among them, the chromium electroplating solution contains: chromium sulfate 80 g / L, sodium acetate 20 g / L, sodium sulfite 40 g / L, sodium dodecyl sulfate 0.8 g / L.

[0041] Example 2. A method for preparing a lightweight aluminum casting for the front and rear covers of a gearbox, comprising the following steps:

[0042] Compared with Example 1, the electroplating layer thickness in step S21 is increased in this example;

[0043] S1. Prepare the aluminum casting matrix;

[0044] S11. After weighing and proportioning each component raw material, under the protection of an argon atmosphere, put it into a melting furnace, heat it to melt until it becomes liquid, add a refining agent, refine and skim the slag, then place the molten metal in a holding furnace, let it stand for 30 min, take out and remove the top 20 - mm - thick molten metal on the surface of the molten metal, and then die - cast the remaining molten metal. During die - casting, the die - casting mold temperature is 200 °C, the die - casting speed is 2.5 m / s. After die - casting, obtain the die - cast blank;

[0045] S12. After cooling the die-cast blank to room temperature, take out the blank, remove the burrs on the surface of the die-cast blank by sanding, and then perform shot peening on the surface of the casting to obtain the aluminum casting matrix;

[0046] S2. Prepare lightweight aluminum castings;

[0047] S21. Place the aluminum casting blank prepared in step S12 in a copper electroplating solution. During electroplating, set the temperature to 68 °C and the current density to 0.5 A / dm 2 , and the electroplating thickness is 1.5 μm;

[0048] Among them, the copper electroplating solution contains: 150 g / L of copper sulfate, 50 g / L of nickel sulfate, 8 g / L of sodium acetate, 20 g / L of boric acid, and 0.5 g / L of sodium dodecylbenzenesulfonate;

[0049] S22. After washing the surface of the aluminum casting blank treated in step S21 with absolute ethanol, protect it in an argon atmosphere, heat it to 380 °C, keep it warm for 150 min, then cool it to room temperature, and then place it in a nickel-copper electroplating solution. Control the electroplating temperature at 45 °C and the current density at 5 A / dm 2 , and the electroplating thickness is 3 μm;

[0050] Among them, the nickel-copper electroplating solution contains: 130 g / L of nickel sulfate, 45 g / L of copper sulfate, 14 g / L of sodium acetate, 25 g / L of boric acid, and 0.5 g / L of sodium dodecylbenzenesulfonate;

[0051] S23. After rinsing the surface of the aluminum casting blank treated in step S22 with deionized water, place it in a nickel-chromium electroplating solution. Control the electroplating temperature at 60 °C and the current density at 2 A / dm 2 , and the electroplating thickness is 0.5 μm;

[0052] Among them, the nickel-chromium electroplating solution contains: 50 g / L of nickel sulfate, 50 g / L of chromium sulfate, 15 g / L of sodium acetate, 30 g / L of sodium sulfite, and 0.8 g / L of sodium dodecyl sulfate;

[0053] S24. After rinsing the surface of the aluminum casting blank treated in step S23 with deionized water, place it in a chromium electroplating solution again. Control the electroplating temperature at 80 °C and the current density at 1 A / dm 2 , and the electroplating thickness is 0.2 μm. After electroplating, rinse and dry the surface of the aluminum casting blank with absolute ethanol. Under an argon atmosphere, heat the aluminum casting blank to 400 °C, keep it warm for 1 h, then heat it to 550 °C again, keep it warm for 4 h, then cool it to 370 °C, keep it warm for 1.5 h again, stop heating, and cool it to room temperature with the furnace to obtain lightweight aluminum castings for the front and rear covers of the gearbox;

[0054] Among them, the chromium electroplating solution contains: 80 g / L of chromium sulfate, 20 g / L of sodium acetate, 40 g / L of sodium sulfite, and 0.8 g / L of sodium dodecyl sulfate.

[0055] Example 3. A method for preparing a lightweight aluminum casting for the front and rear covers of a gearbox, comprising the following steps:

[0056] Compared with Example 2, in this example, the thickness of the electroplated layer in step S22 is increased;

[0057] S1. Prepare the aluminum casting matrix;

[0058] S11. After weighing and proportioning each component raw material, under the protection of an argon atmosphere, put it into a melting furnace, heat it to melt until it becomes liquid, add a refining agent, after refining and skimming the slag, place the molten metal in a holding furnace, let it stand for 30 min, then remove the top 20 mm thick molten metal on the surface of the molten metal, and then die-cast the remaining molten metal. During die-casting, the temperature of the die-casting mold is 200 °C, and the die-casting speed is 2.5 m / s. After die-casting, a die-cast blank is obtained;

[0059] S12. After cooling the die-cast blank to room temperature, take out the blank, use sandpaper to polish and remove the burrs on the die-cast blank, and then perform shot peening on the surface of the casting to obtain the aluminum casting matrix;

[0060] S2. Prepare the lightweight aluminum casting;

[0061] S21. Place the aluminum casting blank prepared in step S12 in a copper electroplating solution. During electroplating, set the temperature to 68 °C and the current density to 0.5 A / dm 2 , and the electroplating thickness is 1.5 μm;

[0062] Among them, the copper electroplating solution contains: 150 g / L of copper sulfate, 50 g / L of nickel sulfate, 8 g / L of sodium acetate, 20 g / L of boric acid, and 0.5 g / L of sodium dodecylbenzenesulfonate;

[0063] S22. After washing the surface of the aluminum casting blank treated in step S21 with absolute ethanol, under the protection of an argon atmosphere, heat it to 380 °C, keep it warm for 150 min, then cool it to room temperature, and then place it in a nickel-copper electroplating solution. Control the electroplating temperature to 45 °C and the current density to 5 A / dm 2 , and the electroplating thickness is 5 μm;

[0064] Among them, the nickel-copper electroplating solution contains: 130 g / L of nickel sulfate, 45 g / L of copper sulfate, 14 g / L of sodium acetate, 25 g / L of boric acid, and 0.5 g / L of sodium dodecylbenzenesulfonate;

[0065] S23. After rinsing the surface of the aluminum casting blank processed in step S22 with deionized water, place it in a nickel-chromium electroplating solution, control the electroplating temperature at 60 °C, and the current density at 2 A / dm 2 , and the electroplating thickness is 0.5 μm;

[0066] Among them, the nickel-chromium electroplating solution contains: nickel sulfate 50 g / L, chromium sulfate 50 g / L, sodium acetate 15 g / L, sodium sulfite 30 g / L, sodium dodecyl sulfate 0.8 g / L;

[0067] S24. After rinsing the surface of the aluminum casting blank processed in step S23 with deionized water, place it in a chromium electroplating solution again, control the electroplating temperature at 80 °C, and the current density at 1 A / dm 2 , the electroplating thickness is 0.2 μm. After electroplating, rinse and dry the surface of the aluminum casting blank with absolute ethanol. Under an argon atmosphere, heat the aluminum casting blank to 400 °C, hold for 1 h, then heat it to 550 °C again, hold for 4 h, cool to 370 °C, hold for 1.5 h again, stop heating, and cool it to room temperature with the furnace to obtain a lightweight aluminum casting for the front and rear covers of the gearbox;

[0068] Among them, the chromium electroplating solution contains: chromium sulfate 80 g / L, sodium acetate 20 g / L, sodium sulfite 40 g / L, sodium dodecyl sulfate 0.8 g / L.

[0069] Example 4. A method for preparing a lightweight aluminum casting for the front and rear covers of a gearbox, comprising the following steps:

[0070] Compared with Example 3, the electroplating layer thickness in step S23 is increased in this example;

[0071] S1. Prepare the aluminum casting matrix;

[0072] S11. After weighing and proportioning each component of the raw materials, under the protection of an argon atmosphere, put them into a melting furnace, heat and melt to a liquid state, add a refining agent, refine and skim the slag, then place the molten metal in a holding furnace, let it stand for 30 min, remove the top 20 mm thick molten metal on the surface of the molten metal, and then cast the remaining molten metal. During casting, the temperature of the casting die is 200 °C, and the casting speed is 2.5 m / s. After casting, obtain a casting blank;

[0073] S12. After cooling the casting blank to room temperature, take out the blank, use sandpaper to polish and remove the burrs on the casting blank, and perform shot peening on the surface of the casting to obtain the aluminum casting matrix;

[0074] S2. Prepare a lightweight aluminum casting;

[0075] S21. Place the aluminum casting blank prepared in step S12 into the copper electroplating solution. During electroplating, set the temperature to 68 °C and the current density to 0.5 A / dm 2 , and the electroplating thickness is 1.5 μm;

[0076] Among them, the copper electroplating solution contains: 150 g / L of copper sulfate, 50 g / L of nickel sulfate, 8 g / L of sodium acetate, 20 g / L of boric acid, and 0.5 g / L of sodium dodecylbenzenesulfonate;

[0077] S22. After washing the surface of the aluminum casting blank treated in step S21 with absolute ethanol, under the protection of an argon atmosphere, heat it to 380 °C, keep it warm for 150 min, then cool it to room temperature, and place it in the nickel-copper electroplating solution. Control the electroplating temperature at 45 °C and the current density at 5 A / dm 2 , and the electroplating thickness is 5 μm;

[0078] Among them, the nickel-copper electroplating solution contains: 130 g / L of nickel sulfate, 45 g / L of copper sulfate, 14 g / L of sodium acetate, 25 g / L of boric acid, and 0.5 g / L of sodium dodecylbenzenesulfonate;

[0079] S23. After rinsing the surface of the aluminum casting blank treated in step S22 with deionized water, place it in the nickel-chromium electroplating solution. Control the electroplating temperature at 60 °C and the current density at 2 A / dm 2 , and the electroplating thickness is 1 μm;

[0080] Among them, the nickel-chromium electroplating solution contains: 50 g / L of nickel sulfate, 50 g / L of chromium sulfate, 15 g / L of sodium acetate, 30 g / L of sodium sulfite, and 0.8 g / L of sodium dodecyl sulfate;

[0081] S24. After rinsing the surface of the aluminum casting blank treated in step S23 with deionized water, place it in the chromium electroplating solution again. Control the electroplating temperature at 80 °C and the current density at 1 A / dm 2 , and the electroplating thickness is 0.2 μm. After electroplating, rinse and dry the surface of the aluminum casting blank with absolute ethanol. Under an argon atmosphere, heat the aluminum casting blank to 400 °C, keep it warm for 1 h, then heat it to 550 °C again, keep it warm for 4 h, then cool it to 370 °C, keep it warm for 1.5 h again, stop heating, and cool it to room temperature with the furnace to obtain the lightweight aluminum casting for the front and rear covers of the gearbox;

[0082] Among them, the chromium electroplating solution contains: 80 g / L of chromium sulfate, 20 g / L of sodium acetate, 40 g / L of sodium sulfite, and 0.8 g / L of sodium dodecyl sulfate.

[0083] Example 5. A method for preparing a lightweight aluminum casting for the front and rear covers of a gearbox, comprising the following steps:

[0084] Compared with Example 4, the thickness of the electroplated layer in this example is increased in step S24;

[0085] S1. Prepare the aluminum casting substrate;

[0086] S11. After weighing and proportioning each component raw material, under the protection of an argon atmosphere, put it into a melting furnace. After heating and melting to a liquid state, add a refining agent. After refining and skimming the slag, place the molten metal in a holding furnace. After standing for 30 minutes, remove the molten metal with a thickness of 20 mm from the top layer of the molten metal surface, and then cast the remaining molten metal. During casting, the temperature of the die-casting mold is 200 °C, and the casting speed is 2.5 m / s. After die-casting, a die-cast blank is obtained;

[0087] S12. After cooling the die-cast blank to room temperature, take out the blank, and use sandpaper to polish and remove the burrs on the die-cast blank, and then perform shot peening on the surface of the casting to obtain the aluminum casting substrate;

[0088] S2. Prepare a lightweight aluminum casting;

[0089] S21. Place the aluminum casting blank prepared in step S12 in a copper electroplating solution. During electroplating, set the temperature to 68 °C and the current density to 0.5 A / dm 2 , and the electroplating thickness is 1.5 μm;

[0090] Among them, the copper electroplating solution contains: 150 g / L of copper sulfate, 50 g / L of nickel sulfate, 8 g / L of sodium acetate, 20 g / L of boric acid, and 0.5 g / L of sodium dodecylbenzenesulfonate;

[0091] S22. After washing the surface of the aluminum casting blank treated in step S21 with absolute ethanol, under the protection of an argon atmosphere, heat it to 380 °C, keep it warm for 150 minutes, then cool it to room temperature, and place it in a nickel-copper electroplating solution. Control the electroplating temperature to 45 °C and the current density to 5 A / dm 2 , and the electroplating thickness is 5 μm;

[0092] Among them, the nickel-copper electroplating solution contains: 130 g / L of nickel sulfate, 45 g / L of copper sulfate, 14 g / L of sodium acetate, 25 g / L of boric acid, and 0.5 g / L of sodium dodecylbenzenesulfonate;

[0093] S23. After rinsing the surface of the aluminum casting blank treated in step S22 with deionized water, place it in a nickel-chromium electroplating solution. Control the electroplating temperature to 60 °C and the current density to 2 A / dm 2 , and the electroplating thickness is 1 μm;

[0094] Among them, the nickel-chromium electroplating solution contains: nickel sulfate 50 g / L, chromium sulfate 50 g / L, sodium acetate 15 g / L, sodium sulfite 30 g / L, sodium dodecyl sulfate 0.8 g / L;

[0095] S24. After rinsing the surface of the aluminum casting blank treated in step S23 with deionized water, place it in the chromium electroplating solution again, control the electroplating temperature at 80 °C, and the current density at 1 A / dm 2 , the electroplating thickness is 0.7 μm. After electroplating, rinse and dry the surface of the aluminum casting blank with anhydrous ethanol. Under an argon atmosphere, heat the aluminum casting blank to 400 °C, keep it warm for 1 h, then heat it up to 550 °C again, keep it warm for 4 h, cool it to 370 °C, keep it warm for 1.5 h again, stop heating, and cool it to room temperature with the furnace to obtain a lightweight aluminum casting for the front and rear covers of the gearbox;

[0096] Among them, the chromium electroplating solution contains: chromium sulfate 80 g / L, sodium acetate 20 g / L, sodium sulfite 40 g / L, sodium dodecyl sulfate 0.8 g / L.

[0097] Example 6. A method for preparing a lightweight aluminum casting for the front and rear covers of a gearbox, comprising the following steps:

[0098] Compared with Example 1, in this example, the temperature and current density parameters in steps S22 and S23 are changed;

[0099] S1. Prepare the aluminum casting matrix;

[0100] S11. After weighing and proportioning each component of the raw materials, under the protection of an argon atmosphere, put them into a melting furnace, heat and melt to a liquid state, add a refining agent, refine and skim the slag, then place the molten metal in a holding furnace, let it stand for 30 min, and then remove the top 20 mm thick molten metal on the surface of the molten metal, and then cast the remaining molten metal. During casting, the temperature of the casting mold is 200 °C, and the casting speed is 2.5 m / s. After casting, obtain a casting blank;

[0101] S12. After cooling the casting blank to room temperature, take out the blank, and use sandpaper to polish and remove the burrs on the casting blank, and then perform shot peening on the surface of the casting to obtain the aluminum casting matrix;

[0102] S2. Prepare a lightweight aluminum casting;

[0103] S21. Place the aluminum casting blank prepared in step S12 in the copper electroplating solution. During electroplating, set the temperature at 68 °C and the current density at 0.5 A / dm 2 , and the electroplating thickness is 0.5 μm;

[0104] Among them, the copper electroplating solution contains: 150 g / L of copper sulfate, 50 g / L of nickel sulfate, 8 g / L of sodium acetate, 20 g / L of boric acid, and 0.5 g / L of sodium dodecylbenzenesulfonate;

[0105] S22. After washing the surface of the aluminum casting blank treated in step S21 with absolute ethanol, under the protection of an argon atmosphere, heat it to 360 °C, keep it warm for 150 min, then cool it to room temperature, and place it in the nickel-copper electroplating solution. Control the electroplating temperature at 50 °C and the current density at 4.5 A / dm 2 , and the electroplating thickness is 3 μm;

[0106] Among them, the nickel-copper electroplating solution contains: 130 g / L of nickel sulfate, 45 g / L of copper sulfate, 14 g / L of sodium acetate, 25 g / L of boric acid, and 0.5 g / L of sodium dodecylbenzenesulfonate;

[0107] S23. After rinsing the surface of the aluminum casting blank treated in step S22 with deionized water, place it in the nickel-chromium electroplating solution. Control the electroplating temperature at 70 °C and the current density at 1.5 A / dm 2 , and the electroplating thickness is 0.5 μm;

[0108] Among them, the nickel-chromium electroplating solution contains: 50 g / L of nickel sulfate, 50 g / L of chromium sulfate, 15 g / L of sodium acetate, 30 g / L of sodium sulfite, and 0.8 g / L of sodium dodecyl sulfate;

[0109] S24. After rinsing the surface of the aluminum casting blank treated in step S23 with deionized water, place it in the chromium electroplating solution again. Control the electroplating temperature at 80 °C and the current density at 1 A / dm 2 , and the electroplating thickness is 0.2 μm. After the electroplating is completed, rinse and dry the surface of the aluminum casting blank with absolute ethanol. Under an argon atmosphere, heat the aluminum casting blank to 400 °C, keep it warm for 1 h, then heat it to 550 °C again, keep it warm for 4 h, cool it to 370 °C, keep it warm for 1.5 h again, then stop heating, and cool it to room temperature with the furnace to obtain the lightweight aluminum casting for the front and rear covers of the gearbox;

[0110] Among them, the chromium electroplating solution contains: 80 g / L of chromium sulfate, 20 g / L of sodium acetate, 40 g / L of sodium sulfite, and 0.8 g / L of sodium dodecyl sulfate.

[0111] Example 7. A method for preparing a lightweight aluminum casting for the front and rear covers of a gearbox, comprising the following steps:

[0112] Compared with Example 1, in this example, the copper sulfate content parameter in the electroplating solution in steps S21 and S22 is changed;

[0113] S1. Prepare the aluminum casting matrix;

[0114] S11. After weighing and proportioning each component raw material, under the protection of an argon atmosphere, it is put into a melting furnace. After heating and melting to the liquid state, a refining agent is added. After refining and skimming the slag, the molten metal is placed in a holding furnace. After standing for 30 min, after removing the top 20 mm thick molten metal on the surface of the molten metal, the remaining molten metal is die-cast. During die-casting, the temperature of the die-casting mold is 200 °C, and the die-casting speed is 2.5 m / s. After die-casting, a die-cast blank is obtained;

[0115] S12. After cooling the die-cast blank to room temperature, the blank is taken out, and after using sandpaper to polish and remove the burrs on the die-cast blank, shot peening treatment is carried out on the surface of the casting to obtain an aluminum casting matrix;

[0116] S2. Prepare a lightweight aluminum casting;

[0117] S21. Place the aluminum casting blank prepared in step S12 in a copper electroplating solution. During electroplating, set the temperature to 68 °C and the current density to 0.5 A / dm 2 , and the electroplating thickness is 0.5 μm;

[0118] Among them, the copper electroplating solution contains: 180 g / L of copper sulfate, 50 g / L of nickel sulfate, 8 g / L of sodium acetate, 20 g / L of boric acid, and 0.5 g / L of sodium dodecylbenzenesulfonate;

[0119] S22. After washing the surface of the aluminum casting blank treated in step S21 with absolute ethanol, under the protection of an argon atmosphere, it is heated to 380 °C, held for 150 min, cooled to room temperature, and then placed in a nickel-copper electroplating solution. Control the electroplating temperature to 45 °C and the current density to 5 A / dm 2 , and the electroplating thickness is 3 μm;

[0120] Among them, the nickel-copper electroplating solution contains: 130 g / L of nickel sulfate, 30 g / L of copper sulfate, 14 g / L of sodium acetate, 25 g / L of boric acid, and 0.5 g / L of sodium dodecylbenzenesulfonate;

[0121] S23. After rinsing the surface of the aluminum casting blank treated in step S22 with deionized water, place it in a nickel-chromium electroplating solution. Control the electroplating temperature to 60 °C and the current density to 2 A / dm 2 , and the electroplating thickness is 0.5 μm;

[0122] Among them, the nickel-chromium electroplating solution contains: 50 g / L of nickel sulfate, 50 g / L of chromium sulfate, 15 g / L of sodium acetate, 30 g / L of sodium sulfite, and 0.8 g / L of sodium dodecyl sulfate;

[0123] S24. After rinsing the surface of the aluminum casting blank processed in step S23 with deionized water, place it in the chromium electroplating solution again, control the electroplating temperature at 80 °C, and the current density at 1 A / dm 2 , the electroplating thickness is 0.2 μm. After the electroplating is completed, rinse and dry the surface of the aluminum casting blank with absolute ethanol. Under an argon atmosphere, heat the aluminum casting blank to 400 °C, keep it warm for 1 h, then heat it to 550 °C again, keep it warm for 4 h, cool it to 370 °C, keep it warm for 1.5 h again, stop heating, and cool it to room temperature with the furnace to obtain the lightweight aluminum casting for the front and rear covers of the gearbox;

[0124] Among them, the chromium electroplating solution contains: chromium sulfate 80 g / L, sodium acetate 20 g / L, sodium sulfite 40 g / L, and sodium dodecyl sulfate 0.8 g / L.

[0125] Comparative Example 1. A method for preparing a lightweight aluminum casting for the front and rear covers of a gearbox, comprising the following steps:

[0126] Compared with Example 1, this comparative example does not perform the treatments of steps S21 and S22;

[0127] S1. Prepare the aluminum casting matrix;

[0128] S11. After weighing and proportioning each component raw material, under the protection of an argon atmosphere, put it into a melting furnace, heat and melt it to a liquid state, add a refining agent, refine and skim the slag, then place the molten metal in a holding furnace, let it stand for 30 min, remove the top 20 mm thick molten metal on the surface of the molten metal, and then die-cast the remaining molten metal. During die-casting, the die-casting mold temperature is 200 °C, and the die-casting speed is 2.5 m / s. After the die-casting is completed, obtain the die-cast blank;

[0129] S12. After cooling the die-cast blank to room temperature, take out the blank, use sandpaper to polish and remove the burrs on the die-cast blank, and perform shot peening on the surface of the casting to obtain the aluminum casting matrix;

[0130] S2. Prepare the lightweight aluminum casting;

[0131] S21. After rinsing the surface of the aluminum casting blank with deionized water, place it in the nickel-chromium electroplating solution, control the electroplating temperature at 60 °C, and the current density at 2 A / dm 2 , the electroplating thickness is 0.5 μm;

[0132] Among them, the nickel-chromium electroplating solution contains: nickel sulfate 50 g / L, chromium sulfate 50 g / L, sodium acetate 15 g / L, sodium sulfite 30 g / L, and sodium dodecyl sulfate 0.8 g / L;

[0133] After rinsing the surface of the aluminum casting blank processed in step S21 with deionized water, place it in the chromium electroplating solution again, control the electroplating temperature at 80 °C, and the current density at 1 A / dm 2 , the electroplating thickness is 0.2 μm. After the electroplating is completed, rinse and dry the surface of the aluminum casting blank with absolute ethanol. Under an argon atmosphere, heat the aluminum casting blank to 400 °C, keep it warm for 1 h, then heat it up to 550 °C again, keep it warm for 4 h, cool it to 370 °C, keep it warm for 1.5 h again, stop heating, and cool it to room temperature in the furnace to obtain the lightweight aluminum casting for the front and rear covers of the gearbox;

[0134] Among them, the chromium electroplating solution contains: chromium sulfate 80 g / L, sodium acetate 20 g / L, sodium sulfite 40 g / L, and sodium dodecyl sulfate 0.8 g / L.

[0135] Comparative Example 2. A method for preparing a lightweight aluminum casting for the front and rear covers of a gearbox, comprising the following steps:

[0136] Compared with Example 1, in this comparative example, copper sulfate was not added during the electroplating layer in steps S21 and S22;

[0137] S1. Prepare the aluminum casting matrix;

[0138] S11. After weighing and proportioning each component raw material, under the protection of an argon atmosphere, put it into a melting furnace, heat and melt it to a liquid state, add a refining agent, refine and skim the slag, then place the molten metal in a holding furnace, let it stand for 30 min, remove the top 20 mm thick molten metal on the surface of the molten metal, and then die-cast the remaining molten metal. During die-casting, the die-casting mold temperature is 200 °C, and the die-casting speed is 2.5 m / s. After die-casting, obtain the die-cast blank;

[0139] S12. After cooling the die-cast blank to room temperature, take out the blank, use sandpaper to polish and remove the burrs on the die-cast blank, and perform shot peening on the surface of the casting to obtain the aluminum casting matrix;

[0140] S2. Prepare the lightweight aluminum casting;

[0141] S21. Place the aluminum casting blank prepared in step S12 in the copper electroplating solution. During electroplating, set the temperature at 68 °C and the current density at 0.5 A / dm 2 , the electroplating thickness is 0.5 μm;

[0142] Among them, the copper electroplating solution contains: nickel sulfate 50 g / L, sodium acetate 8 g / L, boric acid 20 g / L, and sodium dodecylbenzenesulfonate 0.5 g / L;

[0143] S22. After washing the surface of the aluminum casting blank processed in step S21 with absolute ethanol, under the protection of an argon atmosphere, heat it to 380 °C, keep it warm for 150 min, then cool it to room temperature, and place it in a nickel-copper electroplating solution. Control the electroplating temperature at 45 °C and the current density at 5 A / dm 2 , and the electroplating thickness is 3 μm;

[0144] Among them, the nickel-copper electroplating solution contains: nickel sulfate 130 g / L, sodium acetate 14 g / L, boric acid 25 g / L, sodium dodecylbenzenesulfonate 0.5 g / L;

[0145] S23. After rinsing the surface of the aluminum casting blank processed in step S22 with deionized water, place it in a nickel-chromium electroplating solution. Control the electroplating temperature at 60 °C and the current density at 2 A / dm 2 , and the electroplating thickness is 0.5 μm;

[0146] Among them, the nickel-chromium electroplating solution contains: nickel sulfate 50 g / L, chromium sulfate 50 g / L, sodium acetate 15 g / L, sodium sulfite 30 g / L, sodium dodecyl sulfate 0.8 g / L;

[0147] S24. After rinsing the surface of the aluminum casting blank processed in step S23 with deionized water, place it in a chromium electroplating solution again. Control the electroplating temperature at 80 °C and the current density at 1 A / dm 2 , and the electroplating thickness is 0.2 μm. After electroplating, rinse and dry the surface of the aluminum casting blank with absolute ethanol. Under an argon atmosphere, heat the aluminum casting blank to 400 °C, keep it warm for 1 h, then heat it to 550 °C again, keep it warm for 4 h, cool it to 370 °C, keep it warm for 1.5 h again, stop heating, and cool it to room temperature with the furnace to obtain lightweight aluminum castings for the front and rear covers of the gearbox;

[0148] Among them, the chromium electroplating solution contains: chromium sulfate 80 g / L, sodium acetate 20 g / L, sodium sulfite 40 g / L, sodium dodecyl sulfate 0.8 g / L.

[0149] Tensile strength test: According to GB / T228-2008, conduct tensile strength tests on the aluminum castings prepared in Examples 1-5 and Comparative Examples 1-2;

[0150] Wear resistance test: Take the aluminum castings prepared in Examples 1-5 and Comparative Examples 1-2, and under room temperature environment, use SUJ2 steel balls to rub them. The normal load is 300 g, the friction rotation speed is 280 rpm, and after rubbing for 30 min, detect the wear scar morphology;

[0151] Heat the aluminum castings prepared in Examples 1-5 and Comparative Examples 1-2 to 140 °C, keep them warm for 10 min, then cool them to -20 °C, repeat the cycle 7 days later, and conduct wear resistance tests on them again;

[0152] Table 1.

[0153]

[0154] Finally, it should be noted that the above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or perform equivalent replacements for some of the technical features. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for preparing lightweight aluminum castings for front and rear covers of a gearbox, characterized in that: The following steps are involved: S1. Preparation of aluminum casting substrate; S11. Melting and die-casting the components to obtain a die-casting body; S12. After the die casting blank is cooled to room temperature, the blank is removed and polished with sandpaper to remove burrs from the die casting blank, and the surface of the casting is shot peened to obtain an aluminum casting matrix; S2. Preparation of lightweight aluminum castings; S21. The aluminum casting blank prepared in step S12 is placed in a copper electroplating solution. During electroplating, the temperature is set to 55-80°C, the current density is 0.5-1A / dm2, and the electroplating thickness is 0.5-1.5μm; the copper electroplating solution contains: 150-180g / L copper sulfate, 40-60g / L nickel sulfate, 8-15g / L sodium acetate, 20-30g / L boric acid, and 0.3-0.8g / L sodium dodecylbenzene sulfonate; S22. After washing the surface of the aluminum casting blank treated in step S21 with anhydrous ethanol, the surface is protected by argon atmosphere, heated to 360-380°C, kept for 2-3 hours, cooled to room temperature, and placed in a nickel-copper electroplating solution, the electroplating temperature is controlled to be 45-50°C, the current density is 4.5-5A / dm2, and the electroplating thickness is 3-5μm; S23. After the surface of the aluminum casting treated in step S22 is rinsed with deionized water, it is placed in a nickel-chromium electroplating solution, the electroplating temperature is controlled to be 60-70°C, the current density is 1.5-2A / dm2, and the electroplating thickness is 0.5-1μm; S24. After rinsing the surface of the aluminum casting blank treated in step S23 with deionized water, place it in the chromium electroplating solution again, control the electroplating temperature to 80-90°C, the current density to 0.5-1A / dm2, and the electroplating thickness to 0.2-0.7μm. After the electroplating is completed, rinse the surface of the aluminum casting blank with anhydrous ethanol and dry it. Under an argon atmosphere, heat the aluminum casting blank to 350-400°C, keep it warm for 0.5-1h, heat it again to 550-590°C, keep it warm for 4-8h, cool it to 350-400°C, keep it warm for 0.5-2h again, stop heating, and cool it to room temperature with the furnace to obtain lightweight aluminum castings for the front and rear covers of the gearbox.

2. The method for preparing a lightweight aluminum casting for a front and rear cover of a gearbox according to claim 1, characterized in that: In terms of weight percentage, the aluminum casting blank comprises Mg 4-10%, Si 6.8-10%, Mn 1.26-2.24%, Cu 5.5-8%, Ni 0.5-1.8%, Y 0.1-0.15%, Zn 5-18%, Sc 0.05-0.1%, and the balance is Al and unavoidable impurities.

3. The method for preparing a lightweight aluminum casting for a front and rear cover of a gearbox according to claim 1, characterized in that: In step S1, the method for preparing the die casting blank is as follows: After weighing and mixing the raw materials of each component, they are put into a smelting furnace under the protection of argon atmosphere. After heating and melting to liquid state, refining agent is added. After refining and slag removal, the molten metal is placed in a holding furnace. After standing for 15-30 minutes, the top 15-30mm thick molten metal on the surface of the molten metal is taken out and the remaining metal is liquid cast. After the die casting is completed, the die casting blank is obtained.

4. The method for preparing a lightweight aluminum casting for a front and rear cover of a gearbox according to claim 1, characterized in that: In step S11, during die casting, the die casting mold temperature is 160-210° C. and the die casting speed is 2.5-3 m / s.

5. The method for preparing a lightweight aluminum casting for a front and rear cover of a gearbox according to claim 1, characterized in that: In step 22, the nickel-copper electroplating solution contains: 100-200 g / L nickel sulfate, 30-45 g / L copper sulfate, 8-15 g / L sodium acetate, 20-30 g / L boric acid, and 0.3-0.8 g / L sodium dodecylbenzene sulfonate.

6. The method for preparing a lightweight aluminum casting for a front and rear cover of a gearbox according to claim 1, characterized in that: In step 23, the nickel-chromium electroplating solution contains: 40-60 g / L nickel sulfate, 40-60 g / L chromium sulfate, 10-20 g / L sodium acetate, 10-40 g / L sodium sulfite, and 0.5-0.8 g / L sodium dodecyl sulfate.

7. The method for preparing a lightweight aluminum casting for a gearbox front and rear cover according to claim 1, characterized in that: In step 24, the chromium electroplating solution contains: 80-120 g / L of chromium sulfate, 10-20 g / L of sodium acetate, 10-40 g / L of sodium sulfite, and 0.5-0.8 g / L of sodium dodecyl sulfate.

8. A lightweight aluminum casting for a front and rear cover of a gearbox prepared by the preparation method according to any one of claims 1 to 7.

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