High-corrosion-resistance Mg-Al-Mn-La die-casting magnesium alloy as well as preparation method and application thereof

Abstract

The invention provides a high-corrosion-resistance Mg-Al-Mn-La die-casting magnesium alloy as well as a preparation method and application thereof, and belongs to the technical field of magnesium alloys. According to the Mg-Al-Mn-La die-casting magnesium alloy and the preparation method thereof, a small amount of La is added into the AM60 magnesium alloy, so that the Mg-Al-Mn-La die-casting magnesium alloy has excellent corrosion resistance, flowability and plasticity. The Mg-Al-Mn-La die-casting magnesium alloy is obtained by sequentially smelting and high-pressure die casting after the alloy raw materials are mixed, and by controlling pressurization of high-pressure die casting, grains of the Mg-Al-Mn-La die-casting magnesium alloy can be effectively refined, the internal porosity can be reduced, dislocation movement can be hindered, and crack propagation can be limited; therefore, the corrosion resistance, plasticity and strength of the Mg-Al-Mn-La die-casting magnesium alloy are improved. The result of the embodiment shows that the high-corrosion-resistance Mg-Al-Mn-La die-casting magnesium alloy provided by the invention has excellent corrosion resistance, and also has excellent plasticity and good flowability at the same time.

Description

Technical Field

[0001] The present invention relates to the technical field of magnesium alloys, and in particular, to a highly corrosion-resistant Mg-Al-Mn-La die-cast magnesium alloy, a preparation method thereof, and an application thereof. Background Art

[0002] At present, the new energy vehicle industry is facing the dual challenges of reducing energy consumption and improving the cruising range of the whole vehicle. Lightweighting is widely regarded as one of the important ways to solve this problem. Magnesium alloys have the characteristics of light weight, good damping and vibration reduction performance, excellent thermal and electrical conductivity, good electromagnetic shielding performance, etc.; moreover, magnesium alloys have good fluidity, which enables magnesium alloys to have a faster production rhythm in the die-casting process; the magnesium alloy melt does not react with die materials such as steel, which makes the service life of the die material longer and the surface quality of the die-cast parts higher. Therefore, magnesium alloys, as a high-quality lightweight material, are of great significance for improving the performance of new energy vehicles.

[0003] However, magnesium alloys have an extremely low electrode potential (-2.37V vs. SHE) and are prone to electrochemical corrosion; the oxide film of magnesium alloys is loose and cannot provide long-term protection like the alumina film of aluminum alloys; this results in relatively poor corrosion resistance of magnesium alloys. In order to improve the corrosion resistance of magnesium alloys, related prior arts adopt processes such as alloying. For example, when improving the corrosion resistance of magnesium alloys by adding alloying elements (such as Al, Zn, etc.), the added alloying elements may affect the fluidity of magnesium alloys. For example, in the commonly used AM50, AM60, and AZ91 die-cast magnesium alloys, alloying element Al is added. Since the Al8Mn5 phase will precipitate before the precipitation of α-Mg, the viscosity of the die-cast magnesium alloy melt is high and the fluidity is poor. And the main precipitation phases of AM50, AM60, and AZ91 die-cast magnesium alloys are Mg 17 Al 12, the potential difference between it and α-Mg is 30 mV, which is likely to cause micro-galvanic corrosion, resulting in the corrosion resistance, high strength and toughness of die-cast magnesium alloys still needing to be improved. Moreover, with the development of the automotive industry, due to the large size, complex structure, long die-casting process, and unique application scenarios of new energy vehicle body super-large and complex magnesium alloy integrated die-castings, higher requirements are put forward for new die-cast magnesium alloy materials: (1) High corrosion resistance. Some areas of the complex and super-large magnesium alloy integrated die-castings for new energy vehicles need to be exposed to the atmospheric environment, requiring the magnesium alloy material to have high bulk corrosion resistance; (2) High fluidity. It is required that the magnesium alloy has very high fluidity to ensure the rapid long-distance filling of the magnesium alloy melt, especially in structures with small holes and uneven wall thickness, where higher fluidity is required; (3) High strength and toughness, especially high plasticity. The complex and super-large magnesium alloy integrated die-castings for new energy vehicles have complex connection requirements, and connection means such as SPR require the magnesium alloy material to have higher plasticity. However, existing commercial die-cast magnesium alloys such as AM50, AM60, and AZ91 cannot fully meet the new requirements of complex and super-large magnesium alloy integrated die-castings for new energy vehicles.

[0004] Therefore, there is an urgent need to provide a die-cast magnesium alloy that has high corrosion resistance while also having high fluidity and high plasticity. Summary of the Invention

[0005] The purpose of the present invention is to provide a high-corrosion-resistant Mg-Al-Mn-La die-cast magnesium alloy, its preparation method and application. The Mg-Al-Mn-La die-cast magnesium alloy provided by the present invention not only has high corrosion resistance but also has high fluidity and high plasticity.

[0006] To achieve the above-mentioned invention purpose, the present invention provides the following technical solutions:

[0007] The present invention provides a high-corrosion-resistant Mg-Al-Mn-La die-cast magnesium alloy, by mass percentage, including: Al 4.0% - 7.0%, Mn 0.1% - 1.0%, La 0.1% - 1.0%, impurity elements ≤ 0.02% and the balance of Mg;

[0008] The high-corrosion-resistant Mg-Al-Mn-La die-cast magnesium alloy is obtained by successively carrying out melting and high-pressure die-casting after mixing alloy raw materials; the pressure boost of the high-pressure die-casting is 250 - 300 bar.

[0009] The present invention also provides a preparation method of the high-corrosion-resistant Mg-Al-Mn-La die-cast magnesium alloy as described in the above technical solution, including: successively carrying out melting and high-pressure die-casting after mixing alloy raw materials; the pressure boost of the high-pressure die-casting is 250 - 300 bar.

[0010] Preferably, the successively carrying out melting and high-pressure die-casting after mixing alloy raw materials includes the following steps:

[0011] (1) The alloy raw materials are melted in a protective atmosphere to obtain an alloy melt; the alloy raw materials include AM60 alloy, Mg-La master alloy, pure Al, and Mg-Mn master alloy;

[0012] (2) The alloy melt obtained in the step (1) is subjected to high-pressure die casting to obtain a highly corrosion-resistant Mg-Al-Mn-La die-cast magnesium alloy;

[0013] The injection speed of the high-pressure die casting is 3-8 m / s, the boost pressure of the high-pressure die casting is 250-300 bar, and the die temperature of the high-pressure die casting is 100-250 °C.

[0014] Preferably, the protective atmosphere in the step (1) is a mixed gas of CO2 and SF6; the volume ratio of CO2 to SF6 is (50-150):1.

[0015] Preferably, the melting of the alloy raw materials in the protective atmosphere in the step (1) includes: in the protective atmosphere, the AM60 alloy ingot is first melted at the first melting temperature to obtain an AM60 alloy melt; the AM60 alloy melt is mixed with pure Al, Mg-Mn master alloy, and Mg-La master alloy, and then second melting is carried out at the second melting temperature to obtain an alloy raw material mixed melt; the alloy raw material mixed melt is allowed to stand and the floating slag is removed at the second melting temperature; the temperature of the second melting is 20-40 °C higher than the temperature of the first melting.

[0016] Preferably, the first melting temperature is 680-760 °C.

[0017] Preferably, the second melting temperature is 700-780 °C.

[0018] Preferably, the standing time is 10-40 min.

[0019] Preferably, slag removal is carried out during the high-pressure die casting in the step (2).

[0020] The present invention also provides the application of the highly corrosion-resistant Mg-Al-Mn-La die-cast magnesium alloy described in the above technical solution or the highly corrosion-resistant Mg-Al-Mn-La die-cast magnesium alloy prepared by the preparation method described in the above technical solution in an integrated die-cast part.

[0021] The present invention provides a highly corrosion-resistant Mg-Al-Mn-La die-cast magnesium alloy, which, by mass percentage, comprises: 4.0% - 7.0% of Al, 0.1% - 1.0% of Mn, 0.1% - 1.0% of La, impurity elements ≤ 0.02%, and the balance of Mg; the highly corrosion-resistant Mg-Al-Mn-La die-cast magnesium alloy is obtained by successively performing smelting and high-pressure die-casting on alloy raw materials after mixing; the pressure boost in the high-pressure die-casting is 250 - 300 bar. By adding a small amount of La to the AM60 magnesium alloy, the Mg-Al-Mn-La die-cast magnesium alloy of the present invention has excellent corrosion resistance, fluidity, and plasticity. First, adding La can also generate Al 17 17 Al 12 phases with a higher active potential than the Mg 11 RE3 phase. The potential difference between the AlLa phase and α-Mg is only 8 mV, reducing the micro-galvanic corrosion phenomenon of the alloy; thereby improving the corrosion resistance of the Mg-Al-Mn-La die-cast magnesium alloy. Second, adding La to the AM60 alloy can effectively reduce the content of the primary precipitation phase Al8Mn5 phase in the melt of the Mg-Al-Mn-La die-cast magnesium alloy during the smelting of the Mg-Al-Mn-La die-cast magnesium alloy, reducing the melt viscosity of the Mg-Al-Mn-La die-cast magnesium alloy, and thereby improving the fluidity of the Mg-Al-Mn-La die-cast magnesium alloy. Moreover, adding La has a purification effect, effectively reducing the content of inclusions in the melt of the Mg-Al-Mn-La die-cast magnesium alloy and improving the purity of the melt of the Mg-Al-Mn-La die-cast magnesium alloy. The present invention obtains the Mg-Al-Mn-La die-cast magnesium alloy by successively performing smelting and high-pressure die-casting on alloy raw materials after mixing. By controlling the pressure boost in the high-pressure die-casting, the grains of the Mg-Al-Mn-La die-cast magnesium alloy can be effectively refined, the internal porosity can be reduced, the dislocation movement can be hindered, and the crack propagation can be restricted, thereby improving the corrosion resistance, plasticity, and strength of the Mg-Al-Mn-La die-cast magnesium alloy. The results of the examples show that the fluidity of the highly corrosion-resistant Mg-Al-Mn-La die-cast magnesium alloy provided by the present invention is 1.7 times that of the AM60 alloy, the corrosion rate of the Mg-Al-Mn-La die-cast magnesium alloy is 40% lower than that of the AM60 alloy, and the elongation is 6% higher than that of the AM60 alloy, having excellent plasticity, good corrosion resistance, and excellent fluidity. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 is the stress-strain curve of the highly corrosion-resistant Mg-Al-Mn-La die-cast magnesium alloy prepared in Example 1 of the present invention and the die-cast AM60 alloy prepared in Comparative Example 1;

[0023] Figure 2 is the stress-strain curve of the die-cast magnesium alloy prepared in Comparative Example 2 of the present invention;

[0024] Figure 3 Corrosion rate diagrams of the highly corrosion-resistant Mg-Al-Mn-La die-cast magnesium alloy prepared in Example 1 of the present invention and the die-cast AM60 alloy prepared in Comparative Example 1;

[0025] Figure 4 Average corrosion rate diagrams of the highly corrosion-resistant Mg-Al-Mn-La die-cast magnesium alloy prepared in Example 1 of the present invention and the die-cast AM60 alloy prepared in Comparative Example 1;

[0026] Figure 5 Corrosion rate diagram of the die-cast AM60 alloy prepared in Comparative Example 2 of the present invention;

[0027] Figure 6 Average corrosion rate diagram of the die-cast AM60 alloy prepared in Comparative Example 1 of the present invention;

[0028] Figure 7 Fluidity test results of the highly corrosion-resistant Mg-Al-Mn-La die-cast magnesium alloy prepared in Example 1 of the present invention and the die-cast AM60 alloy prepared in Comparative Example 1. Detailed implementation manners

[0029] The present invention provides a highly corrosion-resistant Mg-Al-Mn-La die-cast magnesium alloy, which, by mass percentage, includes: Al 4.0% - 7.0%, Mn 0.1% - 1.0%, La 0.1% - 1.0%, impurity elements ≤ 0.02%, and the balance of Mg;

[0030] The highly corrosion-resistant Mg-Al-Mn-La die-cast magnesium alloy is obtained by successively performing smelting and high-pressure die-casting on alloy raw materials; the injection speed of the high-pressure die-casting is 3 - 8 m / s, the boost pressure of the high-pressure die-casting is 250 - 300 bar, and the mold temperature of the high-pressure die-casting is 100 - 250 °C.

[0031] By mass percentage, the highly corrosion-resistant Mg-Al-Mn-La die-cast magnesium alloy provided by the present invention includes Al 4.0% - 7.0%. As an implementation manner of the present invention, the mass percentage of Al can be 4.0%, 5.0%, 5.32%, 6.0% or 7.0%. The added Al in the present invention can dissolve in the Mg matrix, improving the strength and hardness of the magnesium alloy; Al forms intermetallic compound Mg 17 Al 12 which is dispersed at the grain boundaries or within the grains, significantly enhancing the yield strength and creep resistance of the magnesium alloy, making the magnesium alloy have good plasticity; Al can also promote the formation of a denser aluminum oxide film on the surface of the magnesium alloy, enhancing the corrosion resistance of the magnesium alloy.

[0032] By mass percentage, the highly corrosion-resistant Mg-Al-Mn-La die-casting magnesium alloy provided by the present invention includes 0.1% to 1.0% of Mn. As an embodiment of the present invention, the mass percentage of Mn can be 0.1%, 0.2%, 0.29%, 0.3%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9% or 1.0%. By adding Mn, the present invention forms a high-melting-point compound Mn-Fe phase with impurity Fe, reduces the solid solution of free Fe in the Mg matrix, reduces micro-galvanic corrosion, and improves the corrosion resistance of the Mg-Al-Mn-La die-casting magnesium alloy.

[0033] By mass percentage, the highly corrosion-resistant Mg-Al-Mn-La die-casting magnesium alloy provided by the present invention includes 0.1% to 1.0% of La. As an embodiment of the present invention, the mass percentage of La can be 0.1%, 0.2%, 0.3%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9% or 1.0%. By adding La, the present invention can effectively reduce the content of the primary precipitation phase Al8Mn5 phase in the melt of the Mg-Al-Mn-La die-casting magnesium alloy, reduce the viscosity of the melt of the Mg-Al-Mn-La die-casting magnesium alloy, and thus improve the fluidity of the Mg-Al-Mn-La die-casting magnesium alloy. Moreover, adding La can reduce the inclusion content in the melt and improve the purity of the melt of the Mg-Al-Mn-La die-casting magnesium alloy; adding La can also generate an Al 17 Al 12 RE3 phase with a higher active potential than the Mg 11 phase, reduce the micro-galvanic corrosion phenomenon of the Mg-Al-Mn-La die-casting magnesium alloy, and thus improve the corrosion resistance of the Mg-Al-Mn-La die-casting magnesium alloy.

[0034] By mass percentage, the highly corrosion-resistant Mg-Al-Mn-La die-casting magnesium alloy provided by the present invention includes impurity elements ≤ 0.02%. In the examples of the present invention, the impurity elements can be Si and Fe. By adding La, the present invention can reduce the content of impurity elements.

[0035] By mass percentage, the highly corrosion-resistant Mg-Al-Mn-La die-casting magnesium alloy provided by the present invention includes the balance of Mg. In the present invention, the Mg serves as the Mg matrix of the Mg-Al-Mn-La die-casting magnesium alloy.

[0036] In the present invention, the highly corrosion-resistant Mg-Al-Mn-La die-casting magnesium alloy is obtained by successively performing smelting and high-pressure die-casting on alloy raw materials including alloy raw materials.

[0037] In the present invention, the boosting pressure of the high-pressure die casting is preferably 250 to 300 bar. As an embodiment of the present invention, the boosting pressure of the high-pressure die casting can be 250 bar, 260 bar, 270 bar, 280 bar, 290 bar or 300 bar. By controlling the boosting pressure of the high-pressure die casting within the above range, the present invention can compensate for the solidification shrinkage of the melt formed after melting the alloy raw materials and improve the compactness of the casting, effectively refine the grains of the Mg-Al-Mn-La die-cast magnesium alloy, reduce the internal porosity, hinder the movement of dislocations, limit the crack propagation, thereby improving the corrosion resistance, plasticity and strength of the Mg-Al-Mn-La die-cast magnesium alloy.

[0038] The present invention also provides a preparation method of the high-corrosion-resistant Mg-Al-Mn-La die-cast magnesium alloy described in the above technical solution, which includes melting and then performing high-pressure die casting on the alloy raw materials in sequence; the boosting pressure of the high-pressure die casting is 250 to 300 bar.

[0039] In the present invention, the steps of melting and then performing high-pressure die casting on the alloy raw materials in sequence preferably include the following steps:

[0040] (1) Melting the alloy raw materials in a protective atmosphere to obtain an alloy melt; the alloy raw materials include AM60 alloy, Mg-La master alloy, pure Al and Mg-Mn master alloy;

[0041] (2) Performing high-pressure die casting on the alloy melt obtained in step (1) to obtain a high-corrosion-resistant Mg-Al-Mn-La die-cast magnesium alloy;

[0042] The injection speed of the high-pressure die casting is 3 to 8 m / s, the boosting pressure of the high-pressure die casting is 250 to 300 bar, and the die temperature of the high-pressure die casting is 100 to 250 °C.

[0043] The present invention preferably melts the alloy raw materials in a protective atmosphere to obtain an alloy melt.

[0044] In the present invention, the alloy raw materials include AM60 alloy, Mg-La master alloy, pure Al and Mg-Mn master alloy.

[0045] In the present invention, the purities of the AM60 alloy, Mg-La master alloy, pure Al, and Mg-Mn master alloy are independently preferably >99.9%. In the examples of the present invention, the sources of the AM60 alloy, Mg-La master alloy, pure Al, and Mg-Mn master alloy can be Chongqing Yuhua New Material Technology Co., Ltd.

[0046] In the present invention, the amounts of the AM60 alloy, Mg-La master alloy, pure Al, and Mg-Mn master alloy are adjusted according to Al 4.0% - 7.0%, Mn 0.1% - 1.0%, La 0.1% - 1.0%, and the balance of Mg.

[0047] In the present invention, the protective atmosphere is preferably a mixed gas of CO2 and SF6. The present invention uses the mixed gas of CO2 and SF6 as the protective atmosphere. CO2 has good chemical stability and inertness, preventing the metal from reacting with oxygen in the air at high temperatures, thereby avoiding metal oxidation; SF6 can prevent the oxidation and combustion of the magnesium melt. Using the mixed gas of CO2 and SF6 as the protective atmosphere in the present invention can reduce the impurities in the alloy melt.

[0048] In the present invention, the volume ratio of CO2 to SF6 is preferably (50 - 150):1. As an embodiment of the present invention, the volume ratio of CO2 to SF6 can be 50:1, 60:1, 70:1, 80:1, 90:1, 100:1, 110:1, 120:1, 130:1, 140:1, or 150:1. Controlling the volume ratio of CO2 to SF6 within the above range in the present invention is more conducive to improving the purity of the alloy melt.

[0049] The present invention preferably first removes impurities from the alloy raw materials and then melts them in a protective atmosphere. In the examples of the present invention, the method for removing impurities can be: using a grinding wheel grinder to remove the surface oxide layer of the alloy raw materials; then putting the alloy raw materials with the surface oxide layer removed into a drying oven and drying them at 250°C for 30 min. The present invention reduces the impurities in the alloy raw materials by removing impurities.

[0050] In the present invention, the melting of the alloy raw materials in a protective atmosphere preferably includes: in a protective atmosphere, melting the AM60 alloy ingot at a first melting temperature to obtain an AM60 alloy melt; mixing the AM60 alloy melt with pure Al, Mg-Mn master alloy, and Mg-La master alloy and performing secondary melting at a second melting temperature to obtain an alloy raw material mixed melt; standing and removing the dross of the alloy raw material mixed melt at the second melting temperature; the second melting temperature is 20 - 40°C higher than the first melting temperature, preferably 20 - 30°C.

[0051] In the present invention, the melting is preferably carried out in a melting furnace, and the dry crucible used for melting is preferably a low-carbon steel crucible. The present invention has no special limitation on the specific operation of the melting, and conventional melting operations can be adopted.

[0052] The present invention preferably melts the AM60 alloy ingot at a first melting temperature to obtain an AM60 alloy melt.

[0053] In the present invention, the first melting temperature is preferably 680 to 760 °C. As an embodiment of the present invention, the temperature of the first melting can be 680 °C, 690 °C, 700 °C, 710 °C, 720 °C, 730 °C, 740 °C, 750 °C or 760 °C. By controlling the first melting temperature within the above range, the present invention can melt the AM60 alloy ingot. The present invention has no special limitation on the time of the first melting, and it is only necessary to completely melt the AM60 alloy ingot.

[0054] After obtaining the AM60 alloy melt, the present invention preferably mixes the AM60 alloy melt with pure Al, Mg-Mn master alloy and Mg-La master alloy, and performs secondary melting at the second melting temperature to obtain a mixed melt of alloy raw materials.

[0055] In the present invention, the method of mixing the AM60 alloy melt, pure Al, Mg-Mn master alloy and Mg-La master alloy is preferably to sequentially add pure Al, Mg-Mn master alloy and Mg-La master alloy into the AM60 alloy melt.

[0056] The present invention preferably preheats pure Al, Mg-Mn master alloy and Mg-La master alloy and then sequentially adds them into the AM60 alloy melt. In the examples of the present invention, the preheating temperature can be 150 °C.

[0057] In the present invention, the second melting temperature is preferably 700 to 780 °C. As an embodiment of the present invention, the temperature of the second melting can be 700 °C, 710 °C, 720 °C, 730 °C, 740 °C, 750 °C, 760 °C, 770 °C or 780 °C. By controlling the second melting temperature within the above range, the present invention can melt pure Al, Mg-Mn master alloy and Mg-La master alloy. The present invention has no special limitation on the time of the second melting, and it is only necessary to completely melt pure Al, Mg-Mn master alloy and Mg-La master alloy.

[0058] In the present invention, the temperature of the second melting temperature is preferably 20 to 40 °C higher than the first melting temperature. By controlling the temperature of the second melting temperature to be higher than the first melting temperature and within the above temperature range, the present invention can make the AM60 alloy melt, pure Al, Mg-Mn master alloy and Mg-La master alloy have good fluidity when mixed.

[0059] After obtaining the mixed melt of alloy raw materials, the present invention preferably allows the mixed melt of alloy raw materials to stand and remove the floating slag at the second melting temperature in sequence.

[0060] In the present invention, the standing time is preferably 10 to 40 minutes. As an embodiment of the present invention, the standing time can be 10 minutes, 15 minutes, 20 minutes, 25 minutes, 30 minutes, 35 minutes or 40 minutes. By standing, the present invention can enable impurities in the molten mixture to fully form dross.

[0061] The present invention has no special limitation on the method for removing dross, and any conventional method for removing dross during smelting can be used. In the embodiments of the present invention, the method for removing dross can be: evenly coating a slag skimming ladle with a mixed solution of boron nitride and alcohol on the inner and outer surfaces of a long-handled low-carbon steel ladle and a low-carbon steel stirring rod, and using the above ladle to completely skim the dross on the surface of the melt.

[0062] Preferably after removing the dross, the present invention stirs the obtained melt for 5 to 20 minutes, and then cools it to the liquidus of the alloy melt to obtain the alloy melt.

[0063] By stirring, the present invention can make the melt from which the dross has been removed more uniformly mixed.

[0064] In the present invention, the temperature of the alloy melt is preferably 680 to 750 °C, more preferably 700 to 720 °C. By cooling, the present invention can make the temperature of the alloy melt within the above range, close to the liquidus of the alloy melt, which is more conducive to reducing the reaction between the melt and air and reducing the content of oxidation slag during subsequent high-pressure die casting.

[0065] After obtaining the alloy melt, the present invention performs high-pressure die casting on the alloy melt to obtain a highly corrosion-resistant Mg-Al-Mn-La die-cast magnesium alloy.

[0066] The present invention has no special limitation on the device for high-pressure die casting, and any conventional high-pressure die casting device can be used. In the embodiments of the present invention, the device for high-pressure die casting can be a high-pressure die casting machine.

[0067] The present invention has no special limitation on the operation method for high-pressure die casting, and any conventional high-pressure die casting operation method can be used.

[0068] In the present invention, the injection speed of the high-pressure die casting is 3 to 8 m / s. As an embodiment of the present invention, the injection speed of the high-pressure die casting can be 3 m / s, 4 m / s, 5 m / s, 6 m / s, 7 m / s or 8 m / s. In the present invention, the injection speed of the high-pressure die casting refers to the injection speed of the high-pressure die casting device used during high-pressure die casting. In an embodiment of the present invention, the high-pressure die casting device can be a high-pressure die casting machine. By controlling the injection speed of the high-pressure die casting within the above range, the present invention can improve the density, microstructure, mechanical properties and surface quality of the Mg-Al-Mn-La die-cast magnesium alloy, thereby making the Mg-Al-Mn-La die-cast magnesium alloy have excellent plasticity and corrosion resistance.

[0069] In the present invention, the boosting pressure of the high-pressure die casting is preferably 250 to 300 bar. As an embodiment of the present invention, the boosting pressure of the high-pressure die casting can be 250 bar, 260 bar, 270 bar, 280 bar, 290 bar or 300 bar. By controlling the boosting pressure of the high-pressure die casting within the above range, the present invention can compensate for the solidification shrinkage of the melt formed after melting the alloy raw materials and improve the density of the casting, effectively refine the grains of the Mg-Al-Mn-La die-cast magnesium alloy, reduce the internal porosity, hinder the movement of dislocations, and limit the propagation of cracks, thereby improving the plasticity and strength of the Mg-Al-Mn-La die-cast magnesium alloy.

[0070] In the present invention, the die temperature of the high-pressure die casting is 100 to 250 °C. As an embodiment of the present invention, the die temperature of the high-pressure die casting can be 100 °C, 110 °C, 120 °C, 130 °C, 140 °C, 150 °C, 160 °C, 170 °C, 180 °C, 190 °C, 200 °C, 210 °C, 220 °C, 230 °C, 240 °C or 250 °C. By controlling the die temperature of the high-pressure die casting within the above range, the present invention can control the cooling rate of the alloy melt and refine the solidification structure and grain size.

[0071] In the present invention, drossing is preferably carried out during the high-pressure die casting process. The present invention has no special limitation on the operation method of drossing, and any conventional method for drossing the alloy melt can be used. By drossing, the present invention reduces the impurity content of the alloy melt. In an embodiment of the present invention, drossing is preferably carried out by stirring and drossing the alloy melt once every 5 to 20 minutes.

[0072] The present invention preferably cools the obtained casting to room temperature in air after high-pressure die casting to obtain a highly corrosion-resistant Mg-Al-Mn-La die-cast magnesium alloy.

[0073] The method provided by the present invention is simple to operate. By controlling smelting and high-pressure die casting, it can effectively refine the grains of the Mg-Al-Mn-La die-cast magnesium alloy, reduce the internal porosity, hinder the movement of dislocations, and limit the crack propagation, thereby improving the plasticity and strength of the Mg-Al-Mn-La die-cast magnesium alloy.

[0074] The present invention also provides the application of the highly corrosion-resistant Mg-Al-Mn-La die-cast magnesium alloy described in the above technical solution or the highly corrosion-resistant Mg-Al-Mn-La die-cast magnesium alloy prepared by the preparation method described in the above technical solution in an integrated die-cast part.

[0075] The present invention has no special limitation on the method for applying the highly corrosion-resistant Mg-Al-Mn-La die-cast magnesium alloy in an integrated die-cast part, and any method for forming an integrated die-cast part by conventional magnesium alloy die casting can be used.

[0076] Since the Mg-Al-Mn-La die-cast magnesium alloy provided by the present invention has high corrosion resistance, fluidity and plasticity, high-quality complex and super-large magnesium alloy integrated die-cast parts can be obtained.

[0077] Next, the technical solutions in the present invention will be clearly and completely described in conjunction with the embodiments in the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments in the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts belong to the protection scope of the present invention.

[0078] Example 1

[0079] A highly corrosion-resistant Mg-Al-Mn-La die-cast magnesium alloy, by mass percentage, is: Al 5.32%, Mn 0.29%, La 0.20%, impurity elements ≤ 0.02% and the balance of Mg; wherein, the impurity elements are Si and Fe;

[0080] The preparation method of the highly corrosion-resistant Mg-Al-Mn-La die-cast magnesium alloy is:

[0081] (1) First, use a grinding wheel grinder to remove the oxide layer on the surface of the AM60 alloy, Mg-La master alloy, pure Al and Mg-Mn master alloy, then put them into a drying oven, dry at 250 °C for 30 min to remove moisture, and then prepare alloy raw materials according to Al 5.32%, Mn 0.29%, La 0.50% and the balance of Mg;

[0082] Preheat the melting furnace at 500 °C for 60 min; prepare a solution of boron nitride and alcohol according to a mass ratio of 1:2, evenly coat the inner wall of the low-carbon steel crucible with a brush, and put it into a drying oven to dry;

[0083] Under the protection of a mixed gas with a volume ratio of CO2 to SF6 of 100:1, the temperature of the melting furnace is raised to 730 °C, and the AM60 alloy ingot is melted to obtain an AM60 alloy melt; the temperature of the melting furnace is raised to 750 °C, and pure Al preheated to 150 °C, Mg-Mn master alloy and Mg-La master alloy are successively added to the obtained AM60 alloy melt. After all are melted, it is allowed to stand for 30 min, and the scum on the melt surface is removed with a low-carbon steel ladle, and then stirred for 3 min. ， The temperature is lowered to obtain an alloy melt at 720 °C.

[0084] (2) The magnesium alloy release agent is evenly sprayed on the inner wall of the mold. The alloy melt obtained from the middle part of the melt in the crucible in step (1) is poured into the mold preheated to 200 °C in advance. The injection speed of the high-pressure die casting machine is set to 5 m / s and the boosting pressure is set to 290 bar for die casting experiments. After die casting, manual mold removal is carried out and it is cooled to room temperature in the air, thus obtaining a highly corrosion-resistant Mg-Al-Mn-La die-cast magnesium alloy.

[0085] Example 2

[0086] A highly corrosion-resistant Mg-Al-Mn-La die-cast magnesium alloy, by mass percentage, is: Al 5.96%, Mn 0.30%, La 0.31%, impurity elements ≤ 0.02% and the balance of Mg; among them, the impurity elements are Si and Fe.

[0087] The preparation method of the highly corrosion-resistant Mg-Al-Mn-La die-cast magnesium alloy is as follows:

[0088] (1) The AM60 alloy, Mg-La master alloy, pure Al and Mg-Mn master alloy are first polished with a grinding wheel grinder to remove the oxide layer on the surface of the materials, and then placed in a drying oven and dried at 250 °C for 30 min to remove moisture, and then alloy raw materials are prepared according to Al 5.96%, Mn 0.30%, La 0.31% and the balance of Mg.

[0089] The melting furnace is preheated at 500 °C for 60 min; boron nitride and alcohol are mixed into a solution according to a mass ratio of 1:2, and evenly coated on the inner wall of the low-carbon steel crucible with a brush, and then placed in a drying oven and dried.

[0090] Under the protection of a mixed gas with a volume ratio of CO2 to SF6 of 100:1, the temperature of the melting furnace is raised to 730 °C, and the AM60 alloy ingot is melted to obtain an AM60 alloy melt; the temperature of the melting furnace is raised to 750 °C, and pure Al preheated to 150 °C, Mg-Mn master alloy and Mg-La master alloy are successively added to the obtained AM60 alloy melt. After all are melted, let it stand for 30 min, and use a low-carbon steel ladle to remove all the scum on the melt surface, and then stir for 3 min ， Cool down to obtain an alloy melt at a temperature of 720 °C;

[0091] (2) Uniformly spray the magnesium alloy release agent on the inner wall of the mold. Take the alloy melt obtained from the middle part of the melt in the crucible in step (1) and pour it into the mold preheated to 200 °C in advance. Set the injection speed of the high-pressure die casting machine to 5 m / s and the boost pressure to 290 bar for die casting experiments. After die casting, manually remove the mold and cool it to room temperature in the air, then a high-corrosion-resistant Mg-Al-Mn-La die-cast magnesium alloy is obtained.

[0092] Example 3

[0093] A high-corrosion-resistant Mg-Al-Mn-La die-cast magnesium alloy, by mass percentage, is: Al 5.91%, Mn 0.25%, La 0.34%, impurity elements ≤ 0.02% and the balance of Mg; among them, the impurity elements are Si and Fe;

[0094] The preparation method of the high-corrosion-resistant Mg-Al-Mn-La die-cast magnesium alloy is as follows:

[0095] (1) First, use a grinding wheel grinder to remove the oxide layer on the surface of the AM60 alloy, Mg-La master alloy, pure Al and Mg-Mn master alloy, then put them into a drying oven and dry at 250 °C for 30 min to remove moisture, and then prepare alloy raw materials according to Al 5.91%, Mn 0.25%, La 0.34% and the balance of Mg;

[0096] Preheat the melting furnace at 500 °C for 60 min; prepare a solution of boron nitride and alcohol according to a mass ratio of 1:2, evenly coat the inner wall of the low-carbon steel crucible with a brush, and put it into a drying oven to dry;

[0097] Under the protection of a mixed gas with a volume ratio of CO2 to SF6 of 100:1, the temperature of the melting furnace is raised to 730 °C, and the AM60 alloy ingot is melted to obtain an AM60 alloy melt; the temperature of the melting furnace is raised to 750 °C, and pure Al preheated to 150 °C, Mg-Mn master alloy and Mg-La master alloy are successively added to the obtained AM60 alloy melt. After all are melted, let it stand for 30 min, and use a low-carbon steel ladle to remove all the scum on the melt surface, and then stir for 3 min， Cool down to obtain an alloy melt at a temperature of 720 °C;

[0098] (2) Uniformly spray the magnesium alloy release agent on the inner wall of the mold. Take the alloy melt obtained from the middle part of the melt in the crucible in step (1) and inject it into the mold preheated to 200 °C. Set the injection speed of the high-pressure die-casting machine to 5 m / s and the boosting pressure to 290 bar for die-casting experiments. After die-casting, manually remove the mold and cool it to room temperature in the air, then a high corrosion-resistant Mg-Al-Mn-La die-cast magnesium alloy is obtained.

[0099] Comparative Example 1

[0100] A die-cast magnesium alloy, by mass percentage, is: Al 5.94%, Mn 0.31%, impurity elements ≤ 0.02% and the balance of Mg; among them, the impurity elements are Si and Fe;

[0101] (1) First, use a grinding wheel grinder to remove the oxide layer on the surface of the AM60 alloy, pure Al, and Mg-Mn master alloy, then put them into a drying oven and dry at 250 °C for 30 min to remove moisture, and then prepare alloy raw materials according to the ratio of Al 5.94%, Mn 0.31% and the balance of Mg;

[0102] Preheat the melting furnace at 500 °C for 60 min; Prepare a solution of boron nitride and alcohol in a mass ratio of 1:2, evenly apply it on the inner wall of the low-carbon steel crucible with a brush, and put it into a drying oven to dry;

[0103] Under the protection of a mixed gas with a volume ratio of CO2 and SF6 of 100:1, raise the temperature of the melting furnace to 730 °C to melt the AM60 alloy ingot to obtain an AM60 alloy melt; Raise the temperature of the melting furnace to 750 °C, and sequentially add preheated pure Al and Mg-Mn master alloy to the obtained AM60 alloy melt. After all are melted, let it stand for 30 min, use a low-carbon steel ladle to skim off the scum on the surface of the melt to remove the scum, and stir for 3 min; Cool down to an alloy melt at a temperature of 720 °C;

[0104] (2) Uniformly spray the magnesium alloy release agent on the inner wall of the mold. Take the alloy melt obtained from the middle part of the melt in the crucible in step (1) and inject it into the mold preheated to 200 °C. Set the injection speed of the high-pressure die-casting machine to 5 m / s and the boosting pressure to 290 bar for die-casting experiments. After die-casting, manually remove the mold and cool it to room temperature in the air to obtain a die-cast AM60 alloy, which is the die-cast magnesium alloy.

[0105] Comparative Example 2

[0106] A Mg-Al-Mn-La die-casting magnesium alloy, by mass percentage, is as follows: Al 5.32%, Mn 0.29%, La 0.29%, impurity elements ≤ 0.03%, and the balance is Mg; among them, the impurity elements are Si and Fe;

[0107] The preparation method of the Mg-Al-Mn-La die-casting magnesium alloy is as follows:

[0108] (1) First, use a grinding wheel grinder to remove the oxide layer on the surface of the AM60 alloy, Mg-La master alloy, pure Al, and Mg-Mn master alloy, then put them into a drying oven and dry at 250°C for 30 min to remove moisture, and then prepare alloy raw materials according to the ratio of Al 5.32%, Mn 0.29%, La 0.50%, and the balance is Mg;

[0109] Preheat the melting furnace at 500°C for 60 min; prepare a solution of boron nitride and alcohol in a mass ratio of 1:2, evenly coat the inner wall of the low-carbon steel crucible with a brush, and put it into a drying oven to dry;

[0110] Under the protection of a mixed gas with a volume ratio of CO2 and SF6 of 100:1, raise the temperature of the melting furnace to 730°C, melt the AM60 alloy ingot to obtain an AM60 alloy melt; raise the temperature of the melting furnace to 750°C, and sequentially add pure Al preheated to 150°C, Mg-Mn master alloy, and Mg-La master alloy to the obtained AM60 alloy melt. After all are melted, let it stand for 30 min, skim off the scum on the surface of the melt with a low-carbon steel ladle, and stir for 3 min ， Cool down to obtain an alloy melt with a temperature of 720°C;

[0111] (2) Evenly spray the magnesium alloy release agent on the inner wall of the mold, take the alloy melt obtained from the middle part of the melt in the crucible in step (1) and inject it into the mold preheated to 200°C. Set the injection speed of the high-pressure die-casting machine to 5 m / s and the boost pressure to 145 bar for die-casting experiments. After die-casting, manually remove the mold and cool it to room temperature in the air to obtain the die-casting magnesium alloy.

[0112] Test example

[0113] (1) Room temperature mechanical tensile tests were carried out on the highly corrosion-resistant Mg-Al-Mn-La die-cast magnesium alloys prepared in Examples 1 to 3 and the die-cast magnesium alloys prepared in Comparative Examples 1 to 2. The test method was as follows: Standard die-cast tensile specimens were machined in accordance with the national standard (GB / T 13822-2017) and tensile tests were carried out on a CMT5105 electronic universal testing machine. Tensile conditions: The surface of the specimen was polished brightly with sandpaper and tensile tests were carried out at a rate of 3.6 mm / min. The stress-strain curves of the highly corrosion-resistant Mg-Al-Mn-La die-cast magnesium alloy prepared in Example 1 and the die-cast AM60 alloy prepared in Comparative Example 1 are as Figure 1 shown. In Figure 1 , AM60 refers to the stress-strain curve of the die-cast AM60 alloy prepared in Comparative Example 1; Mg-Al-Mn-La refers to the stress-strain curve of the highly corrosion-resistant Mg-Al-Mn-La die-cast magnesium alloy prepared in Example 1. The stress-strain curve of the die-cast magnesium alloy prepared in Comparative Example 2 is as Figure 2 shown; in Figure 2 , the three curves are the curves of parallel tests carried out three times.

[0114] The tensile test results of the highly corrosion-resistant Mg-Al-Mn-La die-cast magnesium alloys prepared in Examples 1 to 3 and the die-cast magnesium alloys prepared in Comparative Examples 1 to 2 are shown in Table 1:

[0115] Table 1 Tensile test results of the highly corrosion-resistant Mg-Al-Mn-La die-cast magnesium alloys prepared in Examples 1 to 3 and the die-cast magnesium alloys prepared in Comparative Examples 1 to 2

[0116]

[0117]

[0118] From Figures 1 - 2 and Table 1, it can be seen that the tensile strength, yield strength and elongation of the highly corrosion-resistant Mg-Al-Mn-La die-cast magnesium alloy prepared by the present invention are all superior to those of the comparative examples, which indicates that the plasticity of the highly corrosion-resistant Mg-Al-Mn-La die-cast magnesium alloy prepared by the present invention is higher than that of the die-cast magnesium alloy prepared by the comparative examples.

[0119] (2) Several metal cubes of 10mm×10mm×3mm were taken from the highly corrosion-resistant Mg-Al-Mn-La die-cast magnesium alloys prepared in Examples 1 to 3 and the die-cast magnesium alloys prepared in Comparative Examples 1 to 2. After treating the samples according to the national standard (GB / T 19746-2018), the cyclic immersion test of the corrosion salt solution of metals and alloys was carried out. The total test time was 168 h (7 days), and the volume of hydrogen gas generated during the corrosion process was recorded every 12 h. To reduce errors, each group of specimens was measured three times and the average value was taken. The results are shown in Table 2. Among them, the corrosion rate diagrams of the die-cast magnesium alloy prepared in Comparative Example 1 and the highly corrosion-resistant Mg-Al-Mn-La die-cast magnesium alloy of Example 1 are as shown in Figure 3 shown, and the average corrosion rate diagrams of the die-cast magnesium alloy prepared in Comparative Example 1 and the highly corrosion-resistant Mg-Al-Mn-La die-cast magnesium alloy of Example 1 are as shown in Figure 4 shown; the corrosion rate diagram of the die-cast magnesium alloy prepared in Comparative Example 2 is as shown in Figure 5 shown. In Figure 5 , the three curves represent the test results of three parallel tests; the average corrosion rate diagram of the die-cast magnesium alloy prepared in Comparative Example 1 is as shown in Figure 6 shown. In Figure 6 , the three data represent the test results of three parallel tests; the corrosion rate data results of the highly corrosion-resistant Mg-Al-Mn-La die-cast magnesium alloys prepared in Examples 1 to 3 and the die-cast magnesium alloys prepared in Comparative Examples 1 to 2 are shown in Table 2.

[0120] Table 2 Corrosion resistance test results of the highly corrosion-resistant Mg-Al-Mn-La die-cast magnesium alloys prepared in Examples 1 to 3 and the die-cast magnesium alloys prepared in Comparative Examples 1 to 2

[0121] Item Corrosion Rate (mm / y) Example 1 0.29 Example 2 0.27 Example 3 0.31 Comparative Example 1 0.48 Comparative Example 2 0.58

[0122] As can be seen from Table 2 and Figures 3 - 6 , the corrosion rate of the die-cast AM60 alloy prepared in Comparative Example 1 of this application is 0.48 mm / y, and the corrosion rate of the die-cast magnesium alloy prepared in Comparative Example 2 is 0.58 mm / y; the corrosion rate of the highly corrosion-resistant Mg-Al-Mn-La die-cast magnesium alloy in Example 1 is 0.29 mm / y, and the corrosion rate of the highly corrosion-resistant Mg-Al-Mn-La die-cast magnesium alloy in Example 2 is 0.27 mm / y; the corrosion rate of the highly corrosion-resistant Mg-Al-Mn-La die-cast magnesium alloy in Example 3 is 0.31 mm / y. This shows that the Mg-Al-Mn-La die-cast magnesium alloy prepared by the present invention has excellent corrosion resistance compared with the die-cast magnesium alloys prepared in Comparative Examples 1 and 2.

[0123] (3) The fluidity of the highly corrosion-resistant Mg-Al-Mn-La die-cast magnesium alloy prepared in Example 1 and the die-cast AM60 alloy prepared in Comparative Example 1 was tested. The test and evaluation were carried out using a recognized spiral die in the industry under the same process, and the results are as Figure 7 shown. In Figure 7 , (a) is the die-cast AM60 alloy prepared in Comparative Example 1, and (b) is the highly corrosion-resistant Mg-Al-Mn-La die-cast magnesium alloy prepared in Example 1. From Figure 7 , it can be seen that the fluidity length of the die-cast AM60 alloy prepared in Comparative Example 1 is 268 mm; the fluidity length of the highly corrosion-resistant Mg-Al-Mn-La die-cast magnesium alloy prepared in Example 1 is 465 mm.

[0124] From the above results, it can be seen that the Mg-Al-Mn-La die-cast magnesium alloy prepared by the present invention has good corrosion resistance, good plasticity and excellent fluidity, enabling it to be used for preparing super-large magnesium alloy automotive die-castings. This is because by adding a small amount of La to the AM60 magnesium alloy in the present invention, the Mg-Al-Mn-La die-cast magnesium alloy has excellent corrosion resistance, fluidity and plasticity; by controlling the boosting pressure of high-pressure die-casting in the present invention, the grains of the Mg-Al-Mn-La die-cast magnesium alloy can be effectively refined, the internal porosity can be reduced, the dislocation movement can be hindered, and the crack propagation can be restricted, thereby improving the corrosion resistance, plasticity and strength of the Mg-Al-Mn-La die-cast magnesium alloy.

[0125] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A highly corrosion-resistant Mg-Al-Mn-La die-cast magnesium alloy, characterized in that, By mass percentage, it includes: Al 4.0% - 7.0%, Mn 0.1% - 1.0%, La 0.1% - 1.0%, impurity elements ≤ 0.02% and the balance of Mg; The high corrosion-resistant Mg-Al-Mn-La die-cast magnesium alloy is obtained by successively melting and high-pressure die-casting after mixing alloy raw materials; the pressure boosting in the high-pressure die-casting is 250 - 300 bar.

2. The preparation method of the high-corrosion-resistant Mg-Al-Mn-La die-casting magnesium alloy according to claim 1, comprising: It is obtained by successively melting and high-pressure die-casting after mixing alloy raw materials; The pressure boosting in the high-pressure die-casting is 250 - 300 bar.

3. The preparation method according to claim 2, characterized in that, The successive melting and high-pressure die-casting after mixing alloy raw materials includes the following steps: (1) Melting the alloy raw materials in a protective atmosphere to obtain an alloy melt; the alloy raw materials include AM60 alloy, Mg-La master alloy, pure Al and Mg-Mn master alloy; (2) Subjecting the alloy melt obtained in step (1) to high-pressure die-casting to obtain a high corrosion-resistant Mg-Al-Mn-La die-cast magnesium alloy; The injection speed in the high-pressure die-casting is 3 - 8 m / s, the pressure boosting in the high-pressure die-casting is 250 - 300 bar, and the die temperature in the high-pressure die-casting is 100 - 250 °C.

4. The preparation method according to claim 3, characterized in that, The protective atmosphere in step (1) is a mixed gas of CO2 and SF6; the volume ratio of CO2 to SF6 is (50 - 150):

1.

5. The preparation method according to claim 3, wherein, The melting of the alloy raw materials in a protective atmosphere in step (1) includes: in a protective atmosphere, melting the AM60 alloy ingot at a first melting temperature to obtain an AM60 alloy melt; mixing the AM60 alloy melt with pure Al, Mg-Mn master alloy and Mg-La master alloy, and performing secondary melting at a second melting temperature to obtain a mixed melt of alloy raw materials; allowing the mixed melt of alloy raw materials to stand and removing dross at the second melting temperature; the second melting temperature is 20 - 40 °C higher than the first melting temperature.

6. The preparation method according to claim 5, characterized in that, The first melting temperature is 680 - 760 °C.

7. The preparation method according to claim 5, wherein The second melting temperature is 700 - 780 °C.

8. The preparation method according to claim 5, characterized in that, The standing time is 10 - 40 min.

9. The preparation method according to claim 3, characterized in that, Slagging is carried out during the high-pressure die-casting process in step (2).

10. Application of the high corrosion-resistant Mg-Al-Mn-La die-cast magnesium alloy according to claim 1 or the high corrosion-resistant Mg-Al-Mn-La die-cast magnesium alloy prepared by the preparation method according to any one of claims 2 - 9 in an integrated die-cast part.

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