Heat-treatment-free Al-Si alloy suitable for large-scale integrated gravity / low-pressure casting forming and preparation method of heat-treatment-free Al-Si alloy

Abstract

The invention relates to a heat treatment-free Al-Si alloy suitable for large-scale integrated gravity / low-pressure casting molding and a preparation method thereof, and the Al-Si alloy comprises the following components in percentage by mass: 8.0%-8.5% of Si, 0.5%-0.7% of Mg, 0.15%-0.25% of Zn, 0.2%-0.25% of Zr, 0.15%-0.25% of Y and the balance of Al and inevitable impurity elements. In the Al-Si alloy, Mg and Zn are added, so that the strength of the alloy is effectively improved on the premise of not influencing the flowability of the alloy; by adding Zr, primary alpha-Al can be refined, and formed Al3Zr can stably exist as a nucleation core; al3Y is generated by adding Y, grains can be further refined, gas dissolved in the alloy is reduced, in addition, Y can be adsorbed on the growth surface of eutectic Si, the original growth mode is changed, and the eutectic Si is converted into a fiber shape from a plate shape.

Description

Technical Field

[0001] The present invention belongs to the technical field of cast aluminum alloys, and particularly relates to a heat-treatment-free Al-Si alloy suitable for large integrated gravity / low-pressure casting and a preparation method thereof. Background Art

[0002] Al-Si alloys are a type of metallic material mainly composed of aluminum and silicon elements. Hypoeutectic Al-Si alloys refer to Al-Si alloys with a silicon content of <12.6 wt%, generally in the range of 5 wt% - 12 wt%. Aluminum-silicon alloys have good casting properties, can fill complex mold cavities and are not prone to hot cracking, making them suitable for manufacturing castings with complex structures. In addition, due to the characteristics of low density, high specific strength, and corrosion resistance of Al-Si alloys, they are widely used in the fields of aerospace, automotive, and digital.

[0003] In recent years, aluminum alloy castings have been developing towards integration, complexity, and thin-walledness. Under such conditions, the performance requirements for aluminum alloy castings are becoming increasingly high, especially for casting performance and mechanical properties, requiring the ability to fill complex cavities and have strong mechanical properties in the as-cast state. Traditional Al-Si alloys have good casting properties but insufficient strength and toughness in the as-cast state, unable to meet the current performance requirements for Al-Si alloys. Although heat treatment strengthening can greatly improve the mechanical properties of Al-Si alloys, it increases costs and carbon emissions. In addition, there is a risk of deformation of castings during the heat treatment process, affecting subsequent use. Therefore, developing a heat-treatment-free high-strength and tough Al-Si alloy has great practical significance. Summary of the Invention

[0004] In view of this, in order to solve the technical problems of high cost, high carbon emissions, and easy deformation of castings in the method of heat treatment strengthening the mechanical properties of Al-Si alloys in the prior art, the present invention provides a heat-treatment-free Al-Si alloy suitable for large integrated gravity / low-pressure casting and a preparation method thereof.

[0005] The technical solutions adopted by the present invention to solve the above technical problems are as follows.

[0006] In a first aspect, the present invention provides a heat-treatment-free Al-Si alloy suitable for large integrated gravity / low-pressure casting, comprising Si: 8.0 wt% - 8.5 wt%, Mg: 0.5 wt% - 0.7 wt%, Zn: 0.15 wt% - 0.25 wt%, Zr: 0.2 wt% - 0.25 wt%, Y: 0.15 wt% - 0.25 wt%, and the balance being Al and unavoidable impurity elements.

[0007] Preferably, it includes Si: 8.0 wt%, Mg: 0.6 wt%, Zn: 0.2 wt%, Zr: 0.2 wt%, Y: 0.15 wt% - 0.25 wt%, and the balance is Al and inevitable impurity elements.

[0008] In a second aspect, the present invention also provides a preparation method of a heat - treatment - free Al - Si alloy applicable to large - scale integrated gravity / low - pressure casting, comprising the following steps:

[0009] Step 1: Weigh pure Al, Al - Si alloy, pure Mg, pure Zn, Al - Y master alloy, and Al - Zr master alloy in proportion;

[0010] Step 2: Melt pure Al and Al - Si alloy at 800 ± 2.5 °C, stir evenly, cool down to 760 ± 2.5 °C for heat preservation, skim off impurities, and obtain a melt;

[0011] Step 3: First, add pure Mg wrapped with aluminum foil to the melt. After it is completely melted, stir evenly and keep it warm; then add pure Zn wrapped with aluminum foil to the melt. After it is completely melted, stir evenly and keep it warm;

[0012] Step 4: Then add Al - Zr master alloy wrapped with aluminum foil to the melt. After it is completely melted, stir evenly and keep it warm; then add Al - Y master alloy wrapped with aluminum foil to the melt. After it is completely melted, stir evenly and keep it warm;

[0013] Step 5: Finally, add a slag - removing agent to the melt, stir evenly, skim off impurities, introduce argon gas into the melt for refining, and skim off impurities again;

[0014] Step 6: Measure the temperature of the refined melt. When the melt cools down to 720 ± 2.5 °C, pour the melt into a steel mold pre - heated to 200 ± 2.5 °C to obtain a casting.

[0015] Preferably, in Step 1, the purity of the pure Al ≥ 99.8%, the purity of the pure Mg ≥ 99.8%, and the purity of the pure Zn ≥ 99.8%.

[0016] Preferably, in Step 1, the Al - Si alloy is an Al - 20 wt% Si alloy, the Al - Y master alloy is an Al - 10 wt% Y master alloy, and the Al - Zr master alloy is Al - 5 wt% Zr.

[0017] Preferably, before using the pure Al, pure Mg, and pure Zn, remove the surface oxide film and pre - heat them to 200 ± 2.5 °C.

[0018] Preferably, in Step 2, the stirring time is 3 min and the heat - preservation time is 20 min.

[0019] Preferably, in step 3, the stirring time is 2 min and the heat preservation time is 5 min.

[0020] Preferably, in step 4, the stirring time is 2 min and the heat preservation time is 10 min.

[0021] Preferably, in step 5, the addition amount of the drossing agent is 1 wt% of the melt mass.

[0022] Preferably, in step 5, the purity of the nitrogen is 99.99% and the nitrogen gas passing time is 2 min.

[0023] Preferably, in step 5, the stirring time is 2 min.

[0024] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0025] The heat-treatable Al-Si alloy applicable to large integrated gravity / low-pressure casting of the present invention adds trace amounts of Mg, Zn, Zr, and Y to the Al-Si alloy. Among them, the addition of Mg and Zn effectively improves the strength of the alloy without affecting the fluidity of the alloy. The addition of Zr plays a role in refining primary α-Al, and the formed Al 3 Zr can stably exist as a nucleation core. The addition of Y generates Al 3 Y can further refine the grains. On the other hand, as a rare earth element, Y can purify the melt, reduce the gas dissolved in the alloy. In addition, Y will adsorb on the growth surface of eutectic Si, change the original growth mode, and make the morphology of eutectic Si change from plate-like to fibrous.

[0026] The heat-treatable Al-Si alloy applicable to large integrated gravity / low-pressure casting of the present invention has low cost and simple operation. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the technical solutions in the embodiments and comparative examples of the present invention, the following will briefly introduce the drawings required in the embodiments and comparative examples. Obviously, the drawings in the following description are only some embodiments and comparative examples of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0028] Figure 1 Among them, (a) and (b) are respectively the tissue pictures of the alloy in Embodiment 1 of the present invention at 50 times and 1000 times;

[0029] Figure 2In the figure, (a) and (b) are the microstructure pictures of the alloy of Embodiment 2 of the present invention at 50 times and 1000 times respectively;

[0030] Figure 3 In the figure, (a) and (b) are the microstructure pictures of the alloy of Comparative Example 1 of the present invention at 50 times and 1000 times respectively;

[0031] Figure 4 In the figure, (a) and (b) are the microstructure pictures of the alloy of Comparative Example 2 of the present invention at 50 times and 1000 times respectively;

[0032] Figure 5 In the figure, (a) and (b) are the microstructure pictures of the alloy of Comparative Example 3 of the present invention at 50 times and 1000 times respectively. Detailed implementation manners

[0033] In order to enable those skilled in the art to better understand the technical solutions of the present invention, the present invention will be further introduced in detail below in conjunction with embodiments and comparative examples.

[0034] Embodiment 1

[0035] An Al-Si alloy prepared in this embodiment, its chemical composition is calculated by mass fraction as follows: Si: 8.3%, Mg: 0.66%, Zn: 0.23%, Zr: 0.23%, Y: 0.16%, and the rest are Al and inevitable impurity elements.

[0036] The preparation method of the Al-Si alloy in this embodiment includes the following steps:

[0037] Step 1: Weigh pure Al, Al-20wt% Si alloy, pure Mg, pure Zn, Al-10wt% Y master alloy and Al-5wt% Zr master alloy according to the above components.

[0038] Step 2: Place pure Al and Al-20wt% Si alloy in a graphite-clay crucible, melt them in a resistance furnace at 800°C. After pure Al and Al-20wt% Si alloy are completely melted, stir for 3 min, then reduce the temperature of the resistance furnace to 760°C and keep it warm for 20 min to remove refractory impurities on the surface of the melt.

[0039] Step 3: Add pure Mg wrapped with aluminum foil, press it into the melt, and after it is completely melted, stir for 2 min and then keep it warm for 5 min; add pure Zn wrapped with aluminum foil, press it into the melt, and after it is completely melted, stir for 2 min and then keep it warm for 5 min.

[0040] Step 4: Add the Al-5wt% Zr master alloy wrapped with aluminum foil, press it into the melt, wait until it is completely melted, stir for 2 min and then keep warm for 10 min; add the Al-10wt% Y master alloy wrapped with aluminum foil, press it into the melt, wait until it is completely melted, stir for 2 min and then keep warm for 10 min.

[0041] Step 5: Add a slag remover accounting for 1wt% of the melt mass, stir for 2 min, skim off the impurities, and then introduce high-purity argon gas (99.99%) into the melt for refining. Ventilate for 2 min and skim off the impurities again.

[0042] Step 6: Measure the temperature of the refined melt. When the melt cools down to 720 °C, pour it into a steel mold preheated to 200 °C to obtain a casting.

[0043] Test the chemical composition of the casting, observe the macrostructure and microstructure of the alloy with a microscope, and test the tensile mechanical properties of the alloy with a universal mechanical testing machine. The results are as Figure 1 shown in Table 1 and Table 2.

[0044] Example 2

[0045] An Al-Si alloy prepared in this example has a chemical composition by mass fraction as follows: Si: 8.21%, Mg: 0.67%, Zn: 0.22%, Zr: 0.25%, Y: 0.25%, and the rest are Al and inevitable impurity elements.

[0046] The preparation method of the Al-Si alloy in this example includes the following steps:

[0047] Step 1: Weigh pure Al, Al-20wt% Si alloy, pure Mg, pure Zn, Al-10wt% Y master alloy and Al-5wt% Zr master alloy according to the above components.

[0048] Step 2: Place pure Al and Al-20wt% Si alloy in a graphite-clay crucible and melt them in an electric resistance furnace at 800 °C. After pure Al and Al-20wt% Si alloy are completely melted, stir for 3 min, reduce the temperature of the electric resistance furnace to 760 °C and then keep warm for 20 min to remove the refractory impurities on the surface of the melt.

[0049] Step 3: Add pure Mg wrapped with aluminum foil, press it into the melt, wait until it is completely melted, stir for 2 min and then keep warm for 5 min; add pure Zn wrapped with aluminum foil, press it into the melt, wait until it is completely melted, stir for 2 min and then keep warm for 5 min.

[0050] Step 4: Add an Al-5wt% Zr master alloy wrapped with aluminum foil, press it into the melt, and wait until it is completely melted. After stirring for 2 min, keep it warm for 10 min; add an Al-10wt% Y master alloy wrapped with aluminum foil, press it into the melt, and wait until it is completely melted. After stirring for 2 min, keep it warm for 10 min.

[0051] Step 5: Add a slag remover accounting for 1wt% of the melt mass, stir for 2 min, skim off the impurities, and then introduce high-purity argon gas (99.99%) into the melt for refining. Ventilate for 2 min and skim off the impurities again.

[0052] Step 6: Measure the temperature of the refined melt. When the melt cools down to 720 °C, pour it into a steel mold preheated to 200 °C to obtain a casting.

[0053] Test the chemical composition of the casting, observe the macrostructure and microstructure of the alloy with a microscope, and test the tensile mechanical properties of the alloy with a universal mechanical testing machine. The results are as Figure 2 shown in Table 1 and Table 2.

[0054] Comparative Example 1

[0055] An Al-Si alloy prepared in this comparative example has the following chemical composition by mass fraction: Si: 8.43%, Mg: 0.68%, Zn: 0.25%, Zr: 0.21%, and the rest are Al and inevitable impurity elements.

[0056] The preparation method of the Al-Si alloy in this comparative example includes the following steps:

[0057] Step 1: Weigh pure Al, an Al-20wt% Si alloy, pure Mg, pure Zn, and an Al-5wt% Zr master alloy according to the above components.

[0058] Step 2: Place pure Al and the Al-20wt% Si alloy in a graphite-clay crucible and melt them in an electric resistance furnace at 800 °C. After all the raw materials are melted, stir for 3 min. Lower the temperature of the electric resistance furnace to 760 °C and keep it warm for 20 min to remove the refractory impurities on the surface of the melt.

[0059] Step 3: Add pure Mg wrapped with aluminum foil, press it into the melt, and wait until it is completely melted. After stirring for 2 min, keep it warm for 5 min; add pure Zn wrapped with aluminum foil, press it into the melt, and wait until it is completely melted. After stirring for 2 min, keep it warm for 5 min.

[0060] Step 4: Add an Al-5wt% Zr master alloy wrapped with aluminum foil, press it into the melt, and wait until it is completely melted. After stirring for 2 min, keep it warm for 10 min.

[0061] Step 5: Add a slag remover accounting for 1 wt% of the melt mass, stir for 2 min, skim off the impurities, then introduce high-purity argon (99.99%) into the melt for refining, ventilate for 2 min, and skim off the impurities again.

[0062] Step 6: Measure the temperature of the refined melt. When the melt cools down to 720 °C, pour it into a steel mold preheated to 200 °C to obtain a casting.

[0063] Test the chemical composition of the casting, observe the macrostructure and microstructure of the alloy with a microscope, and test the tensile mechanical properties of the alloy with a universal mechanical testing machine. The results are as Figure 3 shown in Table 1 and Table 2.

[0064] Comparative Example 2

[0065] An Al-Si alloy prepared in this comparative example has the following chemical composition by mass fraction: Si: 8.33%, Mg: 0.62%, Zn: 0.22%, Y: 0.23%, and the rest are Al and inevitable impurity elements.

[0066] The preparation method of the Al-Si alloy in this comparative example includes the following steps:

[0067] Step 1: Weigh pure Al, Al-20wt% Si alloy, pure Mg, pure Zn, and Al-10wt% Y master alloy according to the above components.

[0068] Step 2: Place pure Al and Al-20wt% Si alloy in a graphite-clay crucible, melt them in an electric resistance furnace at 800 °C. After all the raw materials are melted, stir for 3 min, then reduce the temperature of the electric resistance furnace to 760 °C and keep it warm for 20 min to remove the refractory impurities on the surface of the melt.

[0069] Step 3: Add pure Mg wrapped with aluminum foil, press it into the melt, and after it is completely melted, stir for 2 min and then keep it warm for 5 min; add pure Zn wrapped with aluminum foil, press it into the melt, and after it is completely melted, stir for 2 min and then keep it warm for 5 min.

[0070] Step 4: Add Al-10wt% Y master alloy wrapped with aluminum foil, press it into the melt, and after it is completely melted, stir for 2 min and then keep it warm for 10 min.

[0071] Step 5: Add a slag remover accounting for 1 wt% of the melt mass, stir for 2 min, skim off the impurities, then introduce high-purity argon (99.99%) into the melt for refining, ventilate for 2 min, and skim off the impurities again.

[0072] Step 6: Measure the temperature of the refined melt. When the melt cools down to 720 °C, pour it into a steel mold preheated to 200 °C to obtain a casting.

[0073] The chemical composition of the test castings was measured, the low-magnification and high-magnification structures of the alloy were observed under a microscope, and the tensile mechanical properties of the alloy were tested using a universal mechanical testing machine. The results are as Figure 4 shown in Table 1 and Table 2.

[0074] Comparative Example 3

[0075] An Al-Si alloy prepared in this comparative example has a chemical composition by mass fraction of: Si: 8.46%, Mg: 0.65%, Zn: 0.24%, and the balance is Al and unavoidable impurity elements.

[0076] The preparation method of the Al-Si alloy in this comparative example includes the following steps:

[0077] Step 1: Weigh pure Al, Al-20wt% Si alloy, pure Mg, and pure Zn according to the above components.

[0078] Step 2: Place pure Al and Al-20wt% Si alloy in a graphite-clay crucible and melt them in an electric resistance furnace at 800 °C. After all the raw materials are melted, stir for 3 min. Lower the temperature of the electric resistance furnace to 760 °C and keep it warm for 20 min to remove the refractory impurities on the surface of the melt.

[0079] Step 3: Add pure Mg wrapped with aluminum foil and press it into the melt. After it is completely melted, stir for 2 min and then keep it warm for 5 min. Add pure Zn wrapped with aluminum foil and press it into the melt. After it is completely melted, stir for 2 min and then keep it warm for 5 min.

[0080] Step 4: Add a slag remover accounting for 1wt% of the mass of the melt, stir for 2 min, skim off the impurities, and then introduce high-purity argon gas into the melt for refining. Vent for 2 min and skim off the impurities again.

[0081] Step 5: Measure the temperature of the refined melt. When the melt cools down to 720 °C, pour it into a steel mold preheated to 200 °C to obtain castings.

[0082] The chemical composition of the test castings was measured, the low-magnification and high-magnification structures of the alloy were observed under a microscope, and the tensile mechanical properties of the alloy were tested using a universal mechanical testing machine. The results are as Figure 5 shown in Table 1 and Table 2.

[0083] Table 1 Chemical Compositions of Examples 1, 2 and Comparative Examples 1 - 3 (unit: wt%)

[0084] Group Si Mg Zn Zr Y Others Al Example 1 8.30 0.66 0.23 0.23 0.16 ≤0.15 Balance Example 2 8.21 0.67 0.22 0.25 0.25 ≤0.15 Balance Comparative Example 1 8.43 0.68 0.25 0.21 0 ≤0.15 Balance Comparative Example 2 8.33 0.62 0.22 0 0.23 ≤0.15 Balance Comparative Example 3 8.46 0.65 0.24 0 0 ≤0.15 Balance

[0085] Table 2 Tensile Mechanical Properties of Examples 1, 2 and Comparative Examples 1 - 3

[0086] Group Tensile strength (Mpa) Yield strength (MPa) Elongation rate (%) Example 1 240.9 136.5 6.7 Example 2 249.6 139.3 9.7 Comparative Example 1 232.9 127.8 5.4 Comparative Example 2 232.5 131.3 6.5 Comparative Example 3 227.1 123.6 4.4

[0087] According to Table 2 and Figures 1 to 5 It can be seen that adding Zr to the Al-Si alloy refines the grains to a certain extent, but it cannot modify the eutectic Si. Adding Y alone can modify the eutectic Si well, but the degree of grain refinement is limited. When Zr and Y are added in combination, the grains can be further refined. The grains change from coarse columnar crystals to fine equiaxed crystals, and the eutectic Si grows into fibrous shape, improving the comprehensive mechanical properties of the alloy. It is detected that the tensile strength of the alloy proposed by the present invention reaches 249.6 Mpa, the yield strength reaches 139.3 Mpa, and the elongation reaches 9.7%.

[0088] Obviously, the above embodiments are merely examples given for clear illustration and are not limitations on the embodiments. For those of ordinary skill in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all embodiments here. And the obvious changes or modifications derived therefrom are still within the protection scope of the present invention.

Claims

1. Al-Si alloy, characterized in that It includes Si: 8.0wt%~8.5wt%, Mg: 0.5wt%~0.7wt%, Zn: 0.15wt%~0.25wt%, Zr: 0.2wt%~0.25wt%, Y: 0.15wt%~0.25wt%, and the balance is Al and unavoidable impurity elements.

2. The Al-Si alloy according to claim 1, characterized in that It includes Si: 8.2wt%, Mg: 0.6wt%, Zn: 0.2wt%, Zr: 0.2wt%, Y: 0.15wt% to 0.25wt%, and the balance is Al and inevitable impurity elements.

3. The method for preparing the Al-Si alloy according to claim 1 or 2, comprising the following steps: Step 1: Weigh pure Al, Al-Si alloy, pure Mg, pure Zn, Al-Y master alloy and Al-Zr master alloy in proportion; Step 2: Melt pure Al and Al-Si alloy at 800±2.5℃, stir evenly, cool to 760±2.5℃ and keep warm, skim off impurities to obtain a melt; Step 3: first add pure Mg wrapped with aluminum foil to the melt, wait until it is completely melted, stir evenly, and keep warm; then add pure Zn wrapped with aluminum foil to the melt, wait until it is completely melted, stir evenly, and keep warm; Step 4: then add the Al-Zr master alloy wrapped with aluminum foil to the melt, wait until it is completely melted, stir evenly, and keep warm; then add the Al-Y master alloy wrapped with aluminum foil to the melt, wait until it is completely melted, stir evenly, and keep warm; Step 5: Finally, add a slag remover to the melt, stir evenly, skim off impurities, pass argon gas into the melt for refining, and skim off impurities again; Step 6: Measure the temperature of the melt after refining. When the melt is cooled to 720±2.5°C, pour the melt into a steel mold preheated to 200±2.5°C to obtain a casting.

4. The method for preparing an Al-Si alloy according to claim 3, characterized in that: In step 1, the purity of pure Al is ≥99.8%, the purity of pure Mg is ≥99.8%, and the purity of pure Zn is ≥99.8%.

5. The method for preparing the Al-Si alloy according to claim 3, characterized in that: In step 1, the Al-Si alloy is an Al-20wt% Si alloy, the Al-Y master alloy is an Al-10wt% Y master alloy, and the Al-Zr master alloy is an Al-5wt% Zr.

6. The method for preparing an Al-Si alloy according to claim 3, characterized in that: Before use, the pure Al, pure Mg and pure Zn have their surface oxide films removed and are preheated to 200±2.5°C.

7. The method for preparing an Al-Si alloy according to claim 3, characterized in that: In step 2, the stirring time is 3 minutes and the insulation time is 20 minutes.

8. The method for preparing an Al-Si alloy according to claim 3, characterized in that: In step 3, the stirring time is 2 minutes and the insulation time is 5 minutes.

9. The method for preparing an Al-Si alloy according to claim 3, characterized in that: In step 4, the stirring time is 2 minutes and the insulation time is 10 minutes.

10. The method for preparing an Al-Si alloy according to claim 3, characterized in that: In step 5, the purity of the nitrogen is 99.99%, the ventilation time of the nitrogen is 2 minutes, the stirring time is 2 minutes, and the amount of the slag remover added is 1 wt% of the mass of the melt.

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