Die-casting multi-element high-strength corrosion-resistant magnesium alloy and preparation method thereof

Abstract

The invention discloses a die-casting multi-element high-strength corrosion-resistant magnesium alloy. The die-casting multi-element high-strength corrosion-resistant magnesium alloy comprises the following components in percentage by mass: 5.5%-6.5% of Al, 1.5%-2.2% of RE, 0.5%-0.8% of Sn, 0.2%-0.4% of Y, 0.2%-0.3% of Mn, 0.2%-0.3% of Ca and the balance of Mg. Wherein the mass of Sn, the mass of Y and the mass of Ca meet the formula # imgabs0 #, and in the formula # imgabs0 #, mSn, mY and mCa represent the mass of Sn, the mass of Y and the mass of Ca respectively; rE is mixed rare earth containing Ce and La, and the mass ratio of Ce to La in RE is 7: 3; the invention further discloses a preparation method of the die-casting multi-element high-strength corrosion-resistant magnesium alloy.

Description

Technical Field

[0001] The present invention belongs to the technical field of light metal materials, and in particular relates to a die-cast multi-element high-strength corrosion-resistant magnesium alloy and a preparation method thereof. Background Art

[0002] Amid increasingly stringent energy and environmental requirements, magnesium alloys, with their low density, high specific strength, excellent processability, and recyclability, are widely used in industries such as automotive, aerospace, and electronics, with demand for these alloys continuing to rise. Compared to traditional steel and aluminum alloys, magnesium alloys offer a greater contribution to achieving energy conservation, emission reduction, and the "dual carbon" goals. In recent years, the increasing application of integrated die-casting components has garnered significant attention as a next-generation lightweight material.

[0003] Magnesium alloys have shown significant advantages in lightweighting, but their low strength and insufficient corrosion resistance still restrict their market application. Surface modification treatments (such as micro-arc oxidation, etc.) can improve the corrosion resistance of magnesium alloys. Once the coating on the surface of the magnesium alloy is destroyed, the corrosion rate of the magnesium alloy will be significantly accelerated. In recent years, the mechanical properties or corrosion resistance of magnesium alloys can be improved by introducing rare earth elements and alloying elements. However, if the added elements or the added amounts are unreasonable, it will have a counterproductive effect. For example, in die-cast Mg-Al-RE magnesium alloys, the Zn content affects the formability of die-casting (prone to hot cracking) and weakens the corrosion resistance; the Be element is slightly toxic to the human body; the Sm element is slightly radioactive. These elements are not very suitable for adding to green magnesium alloys.

[0004] Therefore, how to further improve the corrosion resistance while maintaining the safety and high strength of magnesium alloys remains a technical challenge. Summary of the Invention

[0005] The purpose of the present invention is to provide a die-cast multi-element high-strength corrosion-resistant magnesium alloy, which can improve the strength, plasticity and corrosion resistance of the magnesium alloy by adding tin, manganese, calcium and yttrium to the magnesium-aluminum rare earth base material and reasonably setting the addition amount of each element.

[0006] The present invention also provides a method for preparing a die-cast multi-component high-strength corrosion-resistant magnesium alloy. By rationally setting the preparation process, the preparation efficiency of the magnesium alloy can be improved, the purity of the smelted alloy can be ensured, and the comprehensive improvement of the alloy performance can be achieved.

[0007] The technical solution provided by the present invention is:

[0008] A die-cast multi-component high-strength and corrosion-resistant magnesium alloy, wherein the components of the die-cast multi-component high-strength and corrosion-resistant magnesium alloy and the mass fraction of each component are:

[0009] Al: 5.5% to 6.5%, RE: 1.5% to 2.2%, Sn: 0.5% to 0.8%, Y: 0.2% to 0.4%, Mn: 0.2% to 0.3%, Ca: 0.2% to 0.3%, the balance is Mg;

[0010] Among them, the masses of Sn, Y and Ca satisfy:

[0011] Where m Sn 、m Y and m Ca represent the mass of Sn, the mass of Y, and the mass of Ca respectively;

[0012] RE is a mixed rare earth containing Ce and La, and the mass ratio of Ce to La in RE is 7:3.

[0013] A method for preparing a die-cast multi-component high-strength and corrosion-resistant magnesium alloy, for preparing the die-cast multi-component high-strength and corrosion-resistant magnesium alloy, comprises the following steps:

[0014] Step 1: heating the magnesium ingot under the protection of a mixture of N2 and SF6 until it is completely melted to obtain liquid magnesium;

[0015] Step 2: adding an aluminum ingot, a Mg-30RE master alloy, a Mg-Y master alloy, a Mg-Mn master alloy, a Mg-Ca master alloy, a Mg-Sn-Y master alloy, and a Mg-Sn-Ca master alloy to the liquid magnesium at a temperature of 660° C. to 675° C., and heating the mixture to 680° C. to 700° C. to melt the aluminum ingot and the master alloys to obtain a first alloy melt;

[0016] Step 3: adding a tin ingot to the first alloy melt at a temperature of 660° C. to 670° C., stirring the tin ingot after it is completely melted, skimming the slag, and then keeping the temperature to obtain a second alloy melt;

[0017] Step 4: After refining and slagging the second alloy melt, heating it to 680° C. to 710° C. and keeping it at this temperature to obtain a magnesium alloy melt to be die-casted;

[0018] Step 5: pouring the magnesium alloy melt to be die-cast into a die-casting mold, and die-casting the mold to obtain a die-cast multi-element high-strength corrosion-resistant magnesium alloy.

[0019] Preferably, the atomic mass ratio of Sn to Y in the Mg-Sn-Y master alloy is 1:1, and the atomic mass ratio of Sn to Ca in the Mg-Sn-Ca master alloy is 1:1.

[0020] Preferably, before step 1, the method further comprises:

[0021] The magnesium ingot, aluminum ingot, tin ingot, Mg-30RE master alloy, Mg-Y master alloy, Mg-Mn master alloy, Mg-Ca master alloy, Mg-Sn-Y master alloy and Mg-Sn-Ca master alloy are preheated at 100° C. to 120° C. for 30 to 60 minutes under argon protection.

[0022] Preferably, the purity of the magnesium ingot, the purity of the aluminum ingot, and the purity of the tin ingot are all above 99.99% by mass, and the impurity content of the Mg-30RE master alloy, the impurity content of the Mg-Y master alloy, the impurity content of the Mg-Mn master alloy, the impurity content of the Mg-Ca master alloy, the impurity content of the Mg-Sn-Y master alloy, and the impurity content of the Mg-Sn-Ca master alloy are all below 0.02%.

[0023] Preferably, in step 1, the volume ratio of N2 to SF6 is 90:1 to 110:1.

[0024] Preferably, in step three, after the tin ingot is completely melted, it is stirred by a graphite stirring paddle, the stirring paddle speed is 150 to 300 rpm, and the stirring time is 5 to 10 minutes.

[0025] Preferably, in the step 4, dry argon gas is blown into the second alloy melt at 660° C. to 670° C. for refining.

[0026] Preferably, before step 4, the process further includes pre-treating the argon gas blown into the second alloy melt by:

[0027] After the argon gas is deoxygenated and dehydrated, it is heated at 500°C to obtain dry argon gas.

[0028] Preferably, in step five, the temperature of the die-casting mold is 240° C. to 300° C., the pouring temperature is 660° C. to 710° C., the boost pressure is 40 MPa to 50 MPa, and the holding time is 3 to 5 seconds.

[0029] The beneficial effects of the present invention are:

[0030] The die-cast multi-element high-strength corrosion-resistant magnesium alloy and its preparation method provided by the present invention can play the synergistic effect of rare earth elements and alloying elements by setting the main elements of the alloy and combining the multi-element microalloying composition design, and introduce Al-RE phase to partially replace Mg 17 Al 12Phase, introducing submicron-sized MgSnY phase and MgSnCa phase. The synergistic effect of these phases improves the strength of the alloy; the corrosion resistance of the alloy can be improved by the addition of rare earth elements and the solid solution of multiple microalloying elements; at the same time, the second phase with a smaller grain size is formed. Even if local pitting occurs, the corrosion products containing Y, Ca, or Sn accumulate at the grain boundaries, which will weaken the further occurrence of corrosion; the addition of aluminum, calcium, and manganese can not only effectively reduce the combustion of the alloy melt during the smelting process, but also improve the fluidity of the alloy, so that it can better fill the die-casting mold during the die-casting process and reduce defects such as shrinkage cavities and pores; at the same time, the purification of the alloy melt with high-purity and high-temperature argon gas also helps to reduce defects in the casting. While ensuring good casting performance, it solves the problem that existing magnesium alloys cannot achieve both high strength and high corrosion resistance, thereby broadening the application scenarios of die-cast magnesium alloys. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 This is a field emission electron microscope image of Example 3 of the present invention.

[0032] Figure 2 This is a transmission electron microscope image of Example 3 of the present invention.

[0033] Figure 3 This is the electron backscatter diffraction pattern of Example 3 of the present invention.

[0034] Figure 4 This is the optical structure diagram after the corrosion test of Example 3 of the present invention.

[0035] Figure 5 This is the electron backscatter diffraction pattern of Comparative Example 1 of the present invention.

[0036] Figure 6 This is a field emission electron microscope image of comparative example 2 of the present invention.

[0037] Figure 7 This is a field emission electron microscope image of the fracture of the room temperature tensile specimen of Comparative Example 4 of the present invention.

[0038] Figure 8 This is the optical structure diagram of comparative example 5 after the corrosion test of the invention. DETAILED DESCRIPTION

[0039] The present invention will be described in further detail below in conjunction with the accompanying drawings so that those skilled in the art can implement the invention with reference to the description.

[0040] The present invention provides a die-cast multi-element high-strength corrosion-resistant magnesium alloy. The components of the die-cast multi-element high-strength corrosion-resistant magnesium alloy and the mass fraction of each component are: Al: 5.5% to 6.5%, RE: 1.5% to 2.2%, Sn: 0.5% to 0.8%, Y: 0.2% to 0.4%, Mn: 0.2% to 0.3%, Ca: 0.2% to 0.3%, and the balance is Mg; wherein the masses of Sn, Y and Ca meet the following requirements: Where m Sn 、m Y and m Ca represent the mass (fraction) of Sn, the mass (fraction) of Y, and the mass (fraction) of Ca, respectively.

[0041] RE is a mixed rare earth containing Ce and La, and the mass ratio of Ce to La in RE is 7:3.

[0042] The present invention also provides a method for preparing a die-cast multi-component high-strength and corrosion-resistant magnesium alloy, which is used to prepare the die-cast multi-component high-strength and corrosion-resistant magnesium alloy. The specific preparation process is as follows.

[0043] 1. Raw material preparation

[0044] Prepare magnesium ingots, aluminum ingots, tin ingots, Mg-30RE master alloy, Mg-Y master alloy, Mg-Mn master alloy, Mg-Ca master alloy, Mg-Sn-Y master alloy, and Mg-Sn-Ca master alloy. Weigh the raw materials according to the following mass fractions: Al: 5.5%-6.5%, RE: 1.5%-2.2%, Sn: 0.5%-0.8%, Y: 0.2%-0.4%, Mn: 0.2%-0.3%, Ca: 0.2%-0.3%, and the balance Mg.

[0045] And the masses of Sn, Y and Ca satisfy:

[0046] The weighed raw materials were placed in an oven filled with high-purity argon (purity 99.99%) and heated at 100° C. to 120° C. for 30 to 60 minutes.

[0047] 2. Alloy melting and purification

[0048] (1) The magnesium ingot is heated under the protection of a mixture of N2 and SF6 until it is completely melted to obtain liquid magnesium.

[0049] Among them, the volume ratio of N2 and SF6 is 90:1 to 110:1.

[0050] (2) adding an aluminum ingot, a Mg-30RE master alloy, a Mg-Y master alloy, a Mg-Mn master alloy, a Mg-Ca master alloy, a Mg-Sn-Y master alloy, and a Mg-Sn-Ca master alloy to the liquid magnesium at a temperature of 660° C. to 675° C., and raising the temperature to 680° C. to 700° C. to melt the added aluminum ingot and the master alloys to obtain a first alloy melt.

[0051] (3) Adding a tin ingot to the first alloy melt at a temperature of 660°C to 670°C. After the tin ingot is completely melted, stirring is performed using a graphite stirring paddle at a stirring speed of 150 to 300 rpm for 5 to 10 minutes. After stirring, slag treatment is performed, and then the mixture is kept at 660°C to 670°C for 5 to 10 minutes to obtain a second alloy melt.

[0052] Preferably, the purity of the magnesium ingot, the purity of the aluminum ingot, and the purity of the tin ingot are all above 99.99% by mass, and the impurity content of the Mg-30RE intermediate alloy, the impurity content of the Mg-Y intermediate alloy, the impurity content of the Mg-Mn intermediate alloy, the impurity content of the Mg-Ca intermediate alloy, the impurity content of the Mg-Sn-Y intermediate alloy, and the impurity content of the Mg-Sn-Ca intermediate alloy are all below 0.02%.

[0053] (4) Blowing dry high-purity argon gas (purity 99.99%) into the second alloy melt at 660°C to 670°C for refining, and performing slag removal after refining; then raising the temperature to 680°C to 710°C and keeping the temperature for 10 to 30 minutes to obtain a magnesium alloy melt to be die-casted.

[0054] As a preference, the method further includes pre-treating the argon gas blown into the second alloy melt, wherein the method comprises: deoxidizing and dehydrating the argon gas, and then heating the argon gas at 500° C. to obtain high-temperature dry argon gas.

[0055] During the purification process of alloy melts, purchased high-purity argon is often used to directly blow the melt for purification. However, since argon contains trace amounts of water and oxygen, the melt purification effect is reduced, resulting in some small defects such as pores and shrinkage, which reduces the performance of the alloy. Therefore, the method of removing oxygen and water from the argon gas and then heating it at high temperature effectively improves the purity of the alloy melt and reduces defects in the casting.

[0056] 3. Die Casting

[0057] The magnesium alloy melt to be die-cast is poured into a die-casting mold and die-casted to obtain a die-cast multi-element high-strength corrosion-resistant magnesium alloy.

[0058] The die-casting process parameters are: mold temperature of 240°C to 300°C, pouring temperature of 660°C to 710°C, boost pressure of 40MPa to 50MPa, and holding time of 3 to 5 seconds. After die-casting is completed, the casting is removed from the die and air-cooled.

[0059] The alloy composition design principle of the present invention is multi-element alloying. Under the premise of Al and RE as the main elements, alloying elements Sn, Y, Ca and Mn are added. In the Mg-Al binary alloy, Mg is formed first. 17 Al 12 phase; in Mg-RE alloy, Mg-RE phase is formed first; however, in Mg-Al-RE alloy, Al-RE phase is formed first, especially Al 11 RE3 phase (RE = Ce, La). In the Mg-Sn / Y binary alloy, the Mg2Sn / Mg2Y phase is the only second phase, but in the case of the coexistence of Mg-Sn-Y, it preferentially reacts to form the MgSnY ternary phase, which can significantly improve the mechanical properties and corrosion resistance of the alloy. Similarly, MgSnCa is formed preferentially, rather than Al2Ca or Mg2Ca phases. By controlling the addition amount of Ca and Y, the size of the formed MgSnY phase and MgSnCa phase is made smaller, which is beneficial to improving the mechanical properties of the alloy. For this reason, when a small amount of Ca and Y is added, the content of Sn must be limited again, otherwise, in addition to these two ternary phases, a large-sized Mg2Sn phase may also be generated, resulting in a decrease in performance. The present invention can improve the strength, plasticity, modulus and corrosion resistance of the magnesium alloy by reasonably setting the addition amount of each element.

[0060] The technical solutions and effects of the present invention are further described below with reference to specific embodiments and comparative examples.

[0061] Example 1

[0062] 1. Raw material preparation

[0063] The raw materials were weighed according to mass fraction: magnesium ingot, aluminum ingot, tin ingot, Mg-30RE master alloy, Mg-Y master alloy, Mg-Mn master alloy, Mg-Ca master alloy, Mg-Sn-Y master alloy and Mg-Sn-Ca master alloy.

[0064] The weight fractions are: Al: 5.5%, RE: 1.5%, Y: 0.2%, Sn: 0.5%, Mn: 0.2%, Ca: 0.2%, and the balance is Mg. The weighed raw materials were placed in an oven filled with high-purity argon (99.99%) and heated at 100°C for 60 minutes.

[0065] Among them, RE is a mixed rare earth containing Ce and La, and the mass ratio of Ce to La in RE is 7:3.

[0066] Calculated by mass percentage, the purity of the magnesium ingot, the purity of the aluminum ingot, and the purity of the tin ingot are all above 99.99%, and the impurity content of the Mg-30RE master alloy, the impurity content of the Mg-Y master alloy, the impurity content of the Mg-Mn master alloy, the impurity content of the Mg-Ca master alloy, the impurity content of the Mg-Sn-Y master alloy, and the impurity content of the Mg-Sn-Ca master alloy are all below 0.02%.

[0067] Taking burnout into consideration, the actual amount of Sn added is 1.03 times the above content.

[0068] 2. Alloy melting and purification

[0069] First, a dried magnesium ingot is heated to 700°C under the protection of a mixed gas of N2 and SF6 with a volume ratio of 110:1 to completely melt the magnesium ingot, and then an aluminum ingot, Mg-30RE master alloy, Mg-Y master alloy, Mg-Mn master alloy, Mg-Ca master alloy, Mg-Sn-Y master alloy and Mg-Sn-Ca master alloy are added at a temperature of 660°C, and the temperature is raised to 680°C to completely melt the added aluminum ingot and master alloy; then the temperature is lowered to 660°C, and a tin ingot is added and waited for it to completely melt.

[0070] After the alloy is completely melted, it is stirred at 660° C. and a stirring speed of 150 rpm for 10 minutes using a graphite stirring paddle. After stirring, the alloy is skimmed and then kept at 660° C. for 5 minutes.

[0071] After the heat preservation treatment, the alloy melt is refined at 660° C. with high-purity argon (purity 99.99%); after refining, the slag is removed; the melt is then heated to 680° C. and kept warm for 10 minutes to obtain a magnesium alloy melt to be die-casted.

[0072] Among them, the high-purity argon gas used in refining is a high-temperature dry gas obtained by deoxidizing and removing water and then heating at 500°C.

[0073] 3. Die Casting

[0074] The high-temperature magnesium alloy melt is subjected to high-pressure die-casting to obtain a die-cast part. The die-casting process parameters are: pouring temperature of 660°C, mold temperature of 260°C, boost pressure of 40MPa, and holding time of 3 seconds. The casting is then removed from the die-casting mold and air-cooled to obtain a die-cast multi-element high-strength and corrosion-resistant magnesium alloy.

[0075] Example 2

[0076] 1. Raw material preparation

[0077] The raw materials were weighed according to mass fraction: magnesium ingot, aluminum ingot, tin ingot, Mg-30RE master alloy, Mg-Y master alloy, Mg-Mn master alloy, Mg-Ca master alloy, Mg-Sn-Y master alloy and Mg-Sn-Ca master alloy.

[0078] The weight fractions are: Al: 6.5%, RE: 2.2%, Y: 0.4%, Sn: 0.8%, Mn: 0.3%, Ca: 0.3%, and the balance is Mg. The weighed raw materials were placed in an oven filled with high-purity argon (99.99%) and heated at 120°C for 30 minutes.

[0079] Among them, RE is a mixed rare earth containing Ce and La, and the mass ratio of Ce to La in RE is 7:3.

[0080] Calculated by mass percentage, the purity of the magnesium ingot, the purity of the aluminum ingot, and the purity of the tin ingot are all above 99.99%, and the impurity content of the Mg-30RE master alloy, the impurity content of the Mg-Y master alloy, the impurity content of the Mg-Mn master alloy, the impurity content of the Mg-Ca master alloy, the impurity content of the Mg-Sn-Y master alloy, and the impurity content of the Mg-Sn-Ca master alloy are all below 0.02%.

[0081] Taking burnout into consideration, the actual amount of Sn added is 1.03 times the above content.

[0082] 2. Alloy melting and purification

[0083] First, a dried magnesium ingot is heated to 700°C under the protection of a mixed gas of N2 and SF6 with a volume ratio of 90:1 to completely melt the magnesium ingot, and then an aluminum ingot, Mg-30RE master alloy, Mg-Y master alloy, Mg-Mn master alloy, Mg-Ca master alloy, Mg-Sn-Y master alloy and Mg-Sn-Ca master alloy are added at a temperature of 675°C, and the temperature is raised to 700°C to completely melt the added aluminum ingot and master alloy; then the temperature is lowered to 670°C, and a tin ingot is added and waited for it to completely melt.

[0084] After the alloy was completely melted, it was stirred at 670° C. and 300 rpm using a graphite stirring paddle for 5 minutes. After stirring, the alloy was skimmed and then kept warm at 660° C. for 5 minutes.

[0085] After the heat preservation treatment, the alloy melt is refined at 660°C by blowing dry high-purity argon gas (purity 99.99%); after refining, the slag treatment is performed; then the melt is heated to 680°C and kept warm for 10 minutes to obtain the magnesium alloy melt to be die-casted.

[0086] Among them, the high-purity argon gas used in refining is a high-temperature dry gas obtained by deoxidation and dehydration and then heating at 500°C.

[0087] 3. Die Casting

[0088] The high-temperature magnesium alloy melt is subjected to high-pressure die casting to obtain a die-cast part. The die-casting process parameters are: pouring temperature of 710°C, mold temperature of 240°C, boost pressure of 50MPa, and holding time of 5 seconds. The casting is then removed from the die and air-cooled to obtain a die-cast multi-element high-strength and corrosion-resistant magnesium alloy.

[0089] Example 3

[0090] 1. Raw material preparation

[0091] The raw materials were weighed according to mass fraction: magnesium ingot, aluminum ingot, tin ingot, Mg-30RE master alloy, Mg-Y master alloy, Mg-Mn master alloy, Mg-Ca master alloy, Mg-Sn-Y master alloy and Mg-Sn-Ca master alloy.

[0092] The weight fractions are: Al: 5.9%, RE: 1.9%, Y: 0.3%, Sn: 0.7%, Mn: 0.25%, Ca: 0.24%, and the balance is Mg. The weighed raw materials were placed in an oven filled with argon (purity 99.99%) and heated at 120°C for 45 minutes.

[0093] Among them, RE is a mixed rare earth containing Ce and La, and the mass ratio of Ce to La in RE is 7:3.

[0094] Calculated by mass percentage, the purity of the magnesium ingot, the purity of the aluminum ingot, and the purity of the tin ingot are all above 99.99%, and the impurity content of the Mg-30RE master alloy, the impurity content of the Mg-Y master alloy, the impurity content of the Mg-Mn master alloy, the impurity content of the Mg-Ca master alloy, the impurity content of the Mg-Sn-Y master alloy, and the impurity content of the Mg-Sn-Ca master alloy are all below 0.02%.

[0095] Taking burnout into consideration, the actual amount of Sn added is 1.03 times the above content.

[0096] 2. Alloy melting and purification

[0097] First, a dried magnesium ingot is heated to 700°C under the protection of a mixed gas of N2 and SF6 with a volume ratio of 100:1 to completely melt the magnesium ingot, and then a high-purity aluminum ingot, Mg-30RE master alloy, Mg-Y master alloy, Mg-Mn master alloy, Mg-Ca master alloy, Mg-Sn-Y master alloy and Mg-Sn-Ca master alloy are added at a temperature of 670°C, and the temperature is raised to 690°C to completely melt the added aluminum ingot and master alloy; then the temperature is lowered to 665°C, and a tin ingot is added and waited for it to be completely melted.

[0098] After the alloy is completely melted, it is stirred at 665° C. and a stirring speed of 200 rpm for 8 minutes using a graphite stirring paddle. After stirring, the alloy is skimmed and then kept at 665° C. for 8 minutes.

[0099] After the heat preservation treatment, the alloy melt is refined at 665°C by blowing dry high-purity argon gas (purity 99.99%); after refining, the slag treatment is performed; then the melt is heated to 690°C and kept warm for 15 minutes to obtain the magnesium alloy melt to be die-casted.

[0100] Among them, the high-purity argon gas used in refining is a high-temperature dry gas obtained by deoxidizing and removing water and then heating at 500°C.

[0101] 3. Die Casting

[0102] The high-temperature magnesium alloy melt is subjected to high-pressure die casting to obtain a die-cast part. The die-casting process parameters are: pouring temperature of 700°C, mold temperature of 280°C, boost pressure of 45MPa, and holding time of 4 seconds. The casting is then removed from the die and air-cooled to obtain a die-cast multi-element high-strength and corrosion-resistant magnesium alloy.

[0103] Comparative Example 1 (Comparative Example 3 with Example 3 except for the different die-casting process parameters and the same others)

[0104] 1. Raw material preparation

[0105] The raw materials were weighed according to mass fraction: magnesium ingot, aluminum ingot, tin ingot, Mg-30RE master alloy, Mg-Y master alloy, Mg-Mn master alloy, Mg-Ca master alloy, Mg-Sn-Y master alloy and Mg-Sn-Ca master alloy.

[0106] Al: 5.9%, RE: 1.9%, Y: 0.3%, Sn: 0.7%, Mn: 0.25%, Ca: 0.24%, the balance being Mg and unavoidable impurities ≤ 0.2%; the weighed raw materials were placed in an oven filled with high-purity argon and heated at 120°C for 45 minutes;

[0107] Wherein, RE (mixed rare earth) is added in the form of Mg-RE master alloy, wherein the RE is a mixed rare earth containing Ce and La, and the mass ratio of Ce:La in RE is 7:3, and the impurity content of the master alloy is less than 0.02%;

[0108] Calculated by mass percentage, the purity of the magnesium ingot, the purity of the aluminum ingot, and the purity of the tin ingot are all above 99.99%, and the impurity content of the Mg-30RE master alloy, the impurity content of the Mg-Y master alloy, the impurity content of the Mg-Mn master alloy, the impurity content of the Mg-Ca master alloy, the impurity content of the Mg-Sn-Y master alloy, and the impurity content of the Mg-Sn-Ca master alloy are all below 0.02%.

[0109] In the present invention, taking burnout into consideration, as a preferred embodiment, the actual amount of Sn added is 1.03 times the above content.

[0110] 2. Alloy melting and purification

[0111] First, dried pure magnesium is heated under the protection of a mixed gas of N2 and SF6 with a volume ratio of 100:1 until it is completely melted. Then, high-purity aluminum ingots, Mg-30RE master alloy, Mg-Y master alloy, Mg-Mn master alloy, Mg-Ca master alloy, Mg-Sn-Y master alloy and Mg-Sn-Ca master alloy are added at a temperature of 670°C, and the temperature is first raised to 690°C for complete melting; then the temperature is lowered to 665°C, and a high-purity tin ingot is added and waited for it to be completely melted.

[0112] After the alloy is completely melted, it is stirred at 665°C and 200 rpm for 8 minutes using a high-purity graphite stirring paddle. After stirring, the slag is removed and then kept at 665°C for 8 minutes.

[0113] After the heat preservation treatment, the alloy melt is refined at 665°C with high-purity argon (99.99%) that is blown dry; after refining, the slag is removed; then the melt is heated to 690°C and kept warm for 15 minutes to obtain a magnesium alloy melt to be die-casted.

[0114] 3. Die Casting

[0115] The magnesium alloy melt is poured into the preheated barrel of a die-casting machine for high-pressure die-casting to produce a die-cast part. The die-casting process parameters are: pouring temperature of 715°C, die-casting mold temperature of 220°C, boost pressure of 38 MPa, and holding time of 6 seconds. The casting is then removed from the die-casting mold and air-cooled to produce a die-cast multi-element high-strength, corrosion-resistant magnesium alloy.

[0116] Comparative Example 2 (Refining Using Argon Without Deoxygenation and Dehydration)

[0117] 1. Raw material preparation

[0118] The raw materials were weighed according to mass fraction: magnesium ingot, aluminum ingot, tin ingot, Mg-30RE master alloy, Mg-Y master alloy, Mg-Mn master alloy, Mg-Ca master alloy, Mg-Sn-Y master alloy and Mg-Sn-Ca master alloy.

[0119] The weight fractions are: Al: 5.9%, RE: 1.9%, Y: 0.3%, Sn: 0.7%, Mn: 0.25%, Ca: 0.24%, and the balance is Mg. The weighed raw materials were placed in an oven filled with argon (purity 99.99%) and heated at 120°C for 45 minutes.

[0120] Among them, RE is a mixed rare earth containing Ce and La, and the mass ratio of Ce to La in RE is 7:3.

[0121] Calculated by mass percentage, the purity of the magnesium ingot, the purity of the aluminum ingot, and the purity of the tin ingot are all above 99.99%, and the impurity content of the Mg-30RE master alloy, the impurity content of the Mg-Y master alloy, the impurity content of the Mg-Mn master alloy, the impurity content of the Mg-Ca master alloy, the impurity content of the Mg-Sn-Y master alloy, and the impurity content of the Mg-Sn-Ca master alloy are all below 0.02%.

[0122] Taking burnout into consideration, the actual amount of Sn added is 1.03 times the above content.

[0123] 2. Alloy melting and purification

[0124] First, a dried magnesium ingot is heated under the protection of a mixed gas of N2 and SF6 with a volume ratio of 100:1 until it is completely melted. Then, a high-purity aluminum ingot, Mg-30RE master alloy, Mg-Y master alloy, Mg-Mn master alloy, Mg-Ca master alloy, Mg-Sn-Y master alloy and Mg-Sn-Ca master alloy are added at a temperature of 670°C, and the temperature is raised to 690°C to completely melt the added aluminum ingot and master alloy; then the temperature is lowered to 665°C, and a tin ingot is added and waited for it to be completely melted.

[0125] After the alloy is completely melted, it is stirred at 665° C. and a stirring speed of 200 rpm for 8 minutes using a graphite stirring paddle. After stirring, the alloy is skimmed and then kept at 665° C. for 8 minutes.

[0126] After the heat preservation treatment, the alloy melt is refined at 665°C by blowing dry high-purity argon gas (purity 99.99%); after refining, the slag treatment is performed; then the melt is heated to 690°C and kept warm for 15 minutes to obtain the magnesium alloy melt to be die-casted.

[0127] 3. Die Casting

[0128] The high-temperature magnesium alloy melt is subjected to high-pressure die casting to obtain a die-cast part. The die-casting process parameters are: pouring temperature of 700°C, mold temperature of 280°C, boost pressure of 45MPa, and holding time of 4 seconds. The casting is then removed from the die and air-cooled to obtain a die-cast multi-element high-strength and corrosion-resistant magnesium alloy.

[0129] Comparative Example 3 (no Sn added)

[0130] 1. Raw material preparation

[0131] The raw materials were weighed according to mass fraction: magnesium ingot, aluminum ingot, Mg-30RE master alloy, Mg-Y master alloy, Mg-Mn master alloy, and Mg-Ca master alloy.

[0132] The weight fractions are: Al: 5.9%, RE: 1.9%, Y: 0.3%, Mn: 0.25%, Ca: 0.24%, and the balance is Mg. The weighed raw materials were placed in an oven filled with argon (purity 99.99%) and heated at 120°C for 45 minutes.

[0133] Among them, RE is a mixed rare earth containing Ce and La, and the mass ratio of Ce to La in RE is 7:3.

[0134] Calculated by mass percentage, the purity of the magnesium ingot and the purity of the aluminum ingot are both above 99.99%, and the impurity content of the Mg-30RE master alloy, the impurity content of the Mg-Y master alloy, the impurity content of the Mg-Mn master alloy and the impurity content of the Mg-Ca master alloy are all below 0.02%.

[0135] 2. Alloy melting and purification

[0136] First, the dried magnesium ingot is heated to be completely melted under the protection of a mixed gas of N2 and SF6 with a volume ratio of 100:1, and then high-purity aluminum ingot, Mg-30RE master alloy, Mg-Y master alloy, Mg-Mn master alloy and Mg-Ca master alloy are added at a temperature of 670°C, and the temperature is raised to 690°C to completely melt the added aluminum ingot and master alloy.

[0137] After the alloy is completely melted, it is stirred at 665° C. and a stirring speed of 200 rpm for 8 minutes using a graphite stirring paddle. After stirring, the alloy is skimmed and then kept at 665° C. for 8 minutes.

[0138] After the heat preservation treatment, the alloy melt is refined at 665°C by blowing dry high-purity argon gas (purity 99.99%); after refining, the slag treatment is performed; then the melt is heated to 690°C and kept warm for 15 minutes to obtain the magnesium alloy melt to be die-casted.

[0139] Among them, the high-purity argon gas used in refining is a high-temperature dry gas obtained by deoxidizing and removing water and then heating at 500°C.

[0140] 3. Die Casting

[0141] The high-temperature magnesium alloy melt is subjected to high-pressure die casting to obtain a die-cast part. The die-casting process parameters are: pouring temperature of 700°C, mold temperature of 280°C, boost pressure of 45MPa, and holding time of 4 seconds. The casting is then removed from the die and air-cooled to obtain a die-cast multi-element high-strength and corrosion-resistant magnesium alloy.

[0142] Comparative Example 4 (Sn content is high)

[0143] 1. Raw material preparation

[0144] The raw materials were weighed according to mass fraction: magnesium ingot, aluminum ingot, tin ingot, Mg-30RE master alloy, Mg-Y master alloy, Mg-Mn master alloy, Mg-Ca master alloy, Mg-Sn-Y master alloy and Mg-Sn-Ca master alloy.

[0145] Al: 5.9%, RE: 1.9%, Y: 0.3%, Sn: 1.2%, Mn: 0.25%, Ca: 0.24%, the balance being Mg and unavoidable impurities ≤ 0.2%; the weighed raw materials were placed in an oven filled with high-purity argon and heated at 120°C for 45 minutes;

[0146] Among them, RE (mixed rare earth) is added in the form of Mg-RE master alloy, and the RE is a mixed rare earth containing Ce and La, and the mass ratio of Ce:La in RE is 7:3.

[0147] Calculated by mass percentage, the purity of the magnesium ingot, the purity of the aluminum ingot, and the purity of the tin ingot are all above 99.99%, and the impurity content of the Mg-30RE master alloy, the impurity content of the Mg-Y master alloy, the impurity content of the Mg-Mn master alloy, the impurity content of the Mg-Ca master alloy, the impurity content of the Mg-Sn-Y master alloy, and the impurity content of the Mg-Sn-Ca master alloy are all below 0.02%.

[0148] In the present invention, considering the burning loss, as a preferred embodiment, the actual amount of Sn added is 1.03 times the above content;

[0149] 2. Alloy melting and purification

[0150] First, dried pure magnesium is heated under the protection of a mixed gas of N2 and SF6 with a volume ratio of 100:1 until it is completely melted. Then, high-purity aluminum ingots, Mg-RE master alloys, Mg-Y master alloys, Mg-Mn master alloys, Mg-Ca master alloys, Mg-Sn-Y master alloys, and Mg-Sn-Ca master alloys are added at a temperature of 670°C and the temperature is raised to 690°C for the first time to completely melt. The temperature is then lowered to 665°C, and a high-purity tin ingot is added and allowed to completely melt.

[0151] After the alloy is completely melted, it is stirred at 665°C and 200 rpm for 8 minutes using a high-purity graphite stirring paddle. After stirring, the slag is removed and then kept at 665°C for 8 minutes.

[0152] After the heat preservation treatment, the alloy melt is refined at 665°C with high-purity argon (99.99%) that is blown dry; after refining, the slag is removed; then the melt is heated to 690°C and kept warm for 15 minutes to obtain a magnesium alloy melt to be die-casted.

[0153] 3. Die casting:

[0154] The high-temperature magnesium alloy melt is subjected to high-pressure die casting to obtain a die-cast part. The die-casting process parameters are: pouring temperature of 700°C, mold temperature of 280°C, boost pressure of 45MPa, and holding time of 4 seconds. The casting is then removed from the die and air-cooled to obtain a die-cast multi-element high-strength and corrosion-resistant magnesium alloy.

[0155] Comparative Example 5 (AE44 magnesium alloy)

[0156] 1. Raw material preparation

[0157] The raw materials were weighed according to mass fraction: magnesium ingot, aluminum ingot, Mg-30RE master alloy and Mg-Mn master alloy.

[0158] The following raw materials were weighed according to mass fraction: Al: 4%, RE: 3.7%, Mn: 0.34%, and the balance Mg; the weighed raw materials were placed in an oven filled with high-purity argon gas and heated at 120° C. for 45 minutes.

[0159] Among them, RE is a mixed rare earth containing Ce and La, and the mass ratio of Ce to La in RE is 7:3.

[0160] Calculated by mass percentage, the purity of the magnesium ingot and the purity of the aluminum ingot are both above 99.99%, and the impurity content of the Mg-30RE master alloy and the impurity content of the Mg-Mn master alloy are both below 0.02%.

[0161] 2. Alloy melting and purification

[0162] First, the dried pure magnesium is heated to complete melting under the protection of a mixed gas of N2 and SF6 with a volume ratio of 80:1, and then aluminum ingots, Mg-RE master alloys and Mg-Mn master alloys are added at a temperature of 670°C, and the temperature is raised to 690°C for the first time to completely melt the added aluminum ingots and master alloys.

[0163] After the alloy was completely melted, it was stirred at 665° C. and a stirring speed of 200 rpm for 4 minutes using a graphite stirring paddle. After stirring, the alloy was skimmed and then kept at 665° C. for 8 minutes.

[0164] After the heat preservation treatment, the alloy melt is refined at 665°C by blowing dry high-purity argon gas (purity 99.99%); after refining, the slag treatment is performed; then the melt is heated to 690°C and kept warm for 15 minutes to obtain the magnesium alloy melt to be die-casted.

[0165] 3. Die Casting

[0166] The high-temperature magnesium alloy melt was subjected to high-pressure die casting to obtain a die-cast part. The die-casting process parameters were: pouring temperature of 700°C, mold temperature of 280°C, boost pressure of 45MPa, and holding time of 4 seconds. The casting was then removed from the die-casting mold and air-cooled to obtain the die-cast AE44 magnesium alloy.

[0167] The die-cast magnesium alloy prepared in Example 3 was observed by electron microscope. The observation results are as follows: Figure 1-4 The results show that the die-cast magnesium alloy exhibits microstructural characteristics of fine and uniform grain size and significantly refined second phase. These excellent structural characteristics are extremely beneficial to improving the mechanical properties and corrosion resistance of magnesium alloys. At the same time, MgSnY phase ( Figure 3 The presence of this phase further enhances the mechanical properties and corrosion resistance of the alloy. At room temperature, the alloy has good mechanical properties and corrosion resistance, specifically: a tensile strength of 277 MPa, a yield strength of 172 MPa, and an elongation at break of 17.24%; its corrosion rate is 0.092 mg·cm -2 ·d -1 .

[0168] In order to deeply explore the influence of different factors on the performance of die-cast magnesium alloy, a series of comparative examples were set up. Comparative Example 1 was compared with Example 3, in which only the die-casting process parameters were changed. Figure 5It can be clearly seen that the grain size in some areas of Comparative Example 1 is significantly larger. This change in microstructure has led to a decrease in the mechanical properties and corrosion resistance of the alloy to varying degrees. During the smelting process, the alloy of Comparative Example 2 was refined using argon gas that was not deoxidized or dehydrated. This operation left a small amount of gas in the alloy melt, which was not discharged in time during the die-casting process, resulting in obvious shrinkage defects in some parts of the die-casting ( Figure 6 ), which ultimately leads to a significant decrease in the mechanical properties and corrosion resistance of the alloy. Compared with Example 3, the content of Sn element in Comparative Example 4 is too high. Excessive Sn element leads to the formation of a large-sized second phase ( Figure 7 ), which seriously deteriorates the plasticity and corrosion resistance of the alloy. Under the same test conditions, Figure 8 (Corrosion morphology of AE44 magnesium alloy of Comparative Example 5) and Figure 4 (Corrosion morphology of Example 3) It can be found that the surface corrosion pits of Comparative Example 5 are more numerous and deeper, which fully demonstrates that its corrosion resistance is significantly weaker than that of Example 3.

[0169] In order to systematically evaluate the performance of the die-cast magnesium alloys prepared in the various embodiments and comparative examples of the present invention, these alloys were die-cast into standard test bars in accordance with the standards of GB / T228.1-2021 "Tension testing of metallic materials - Part 1: Room temperature test methods" and GB / T228.2-2015 "Tension testing of metallic materials - Part 2: High temperature test methods". The mechanical properties of the magnesium alloys were then tested at room temperature (25°C) and high temperature (175°C) respectively, thereby obtaining detailed mechanical properties data of the magnesium alloys of the present invention. At the same time, an immersion test of the die-cast magnesium alloy was carried out in accordance with GB / T 19291-2003 "Corrosion of metals and alloys - General principles for corrosion testing". After the experiment, the corrosion products on the surface of the corrosion sample were cleaned according to the method of GB / T 16545-2015 "Removal of corrosion products on corrosion test specimens of metals and alloys". The corrosion rate of the die-cast magnesium alloy was calculated by weight loss method to evaluate its corrosion resistance. The above-mentioned indicators were tested for Examples 1-3 and Comparative Examples 1-5 of the present invention, and compared with commercial die-cast AZ91D and AM60B magnesium alloys. The specific test results are shown in Table 1.

[0170] Table 1 Numerical values of corresponding test indicators of the embodiments and comparative examples

[0171]

[0172] It can be clearly seen from the data in Table 1 that the magnesium alloys prepared in Examples 1-3 of the present invention exhibit excellent performance under both room temperature (25°C) and high temperature (150°C) conditions. At room temperature, their tensile strength is between 257 and 289 MPa, their yield strength is between 156 and 182 MPa, and their elongation at break is 15.01 to 18.59%. At high temperature (150°C), their tensile strength is between 195 and 218 MPa, their yield strength is between 143 and 167 MPa, and their elongation at break is 26.32 to 37.21%. In addition, the corrosion rate of the magnesium alloys prepared in Examples 1-3 of the present invention is controlled within a range of 0.092 to 0.256 (mg·cm -2 ·d -1 Compared with commercial die-cast AZ91D and AM60B magnesium alloys, the magnesium alloy prepared by the present invention has significant advantages in mechanical properties and corrosion resistance.

[0173] The present invention successfully obtains an ideal microstructure by cleverly adding trace alloying elements and carefully optimizing the preparation process. This microstructure effectively reduces the number of micro-galvanic couples between the magnesium matrix and the second phase, thereby achieving precise control of the corrosion resistance of the magnesium alloy. At the same time, the dense and uniform corrosion product layer formed during the corrosion process can further inhibit the occurrence and development of corrosion. Specifically, the addition of rare earth elements and alloying elements plays a key role in improving the performance of die-cast magnesium alloys. Rare earth elements (Ce, La, Y) mainly play the role of refining grains, purifying alloys, improving thermal stability and enhancing corrosion resistance in the alloy; while alloying elements (Al, Sn, Mn, Ca) mainly improve the mechanical properties and corrosion resistance of the alloy through mechanisms such as solid solution strengthening, grain refinement strengthening and second phase strengthening.

[0174] In summary, the present invention successfully produces a die-cast magnesium alloy with excellent mechanical properties and a low corrosion rate by scientifically and rationally selecting alloying elements and precisely controlling their addition amounts. This high-performance die-cast magnesium alloy can meet the diverse needs of various engineering fields and is expected to promote the widespread application of magnesium alloys in various fields, including transportation.

[0175] Although specific embodiments of the present invention have been disclosed above, the scope of application of the present invention is not limited to the embodiments listed in the specification and exemplary embodiments. The present invention has broad applicability and can be applied to a variety of suitable fields. Further modifications and optimizations of the present invention are readily apparent to those skilled in the art. Therefore, the present invention is not limited to the specific details and illustrations described herein without departing from the general concept defined by the claims and their equivalents.

Claims

1. A die-cast multi-element high-strength corrosion-resistant magnesium alloy, characterized in that: The components of the die-cast multi-component high-strength corrosion-resistant magnesium alloy and the mass fraction of each component are: Al: 5.5% to 6.5%, RE: 1.5% to 2.2%, Sn: 0.5% to 0.8%, Y: 0.2% to 0.4%, Mn: 0.2% to 0.3%, Ca: 0.2% to 0.3%, the balance is Mg; Among them, the masses of Sn, Y and Ca satisfy: Where m Sn 、m Y and m Ca represent the mass of Sn, the mass of Y, and the mass of Ca respectively; RE is a mixed rare earth containing Ce and La, and the mass ratio of Ce to La in RE is 7:

3.

2. A method for preparing a die-cast multi-component high-strength and corrosion-resistant magnesium alloy, for preparing the die-cast multi-component high-strength and corrosion-resistant magnesium alloy according to claim 1, characterized in that: The steps include: Step 1: heating the magnesium ingot under the protection of a mixture of N2 and SF6 until it is completely melted to obtain liquid magnesium; Step 2: adding an aluminum ingot, a Mg-30RE master alloy, a Mg-Y master alloy, a Mg-Mn master alloy, a Mg-Ca master alloy, a Mg-Sn-Y master alloy, and a Mg-Sn-Ca master alloy to the liquid magnesium at a temperature of 660° C. to 675° C., and heating the mixture to 680° C. to 700° C. to melt the aluminum ingot and the master alloys to obtain a first alloy melt; Step 3: adding a tin ingot to the first alloy melt at a temperature of 660° C. to 670° C., stirring the tin ingot after it is completely melted, skimming the slag, and then keeping the temperature to obtain a second alloy melt; Step 4: After refining and slagging the second alloy melt, heating it to 680° C. to 710° C. and keeping it at this temperature to obtain a magnesium alloy melt to be die-casted; Step 5: pouring the magnesium alloy melt to be die-cast into a die-casting mold, and die-casting the mold to obtain a die-cast multi-element high-strength corrosion-resistant magnesium alloy.

3. The method for preparing the die-cast multi-element high-strength corrosion-resistant magnesium alloy according to claim 2, characterized in that: The atomic mass ratio of Sn to Y in the Mg-Sn-Y master alloy is 1:1, and the atomic mass ratio of Sn to Ca in the Mg-Sn-Ca master alloy is 1:

1.

4. The method for preparing the die-cast multi-element high-strength corrosion-resistant magnesium alloy according to claim 3, characterized in that: Before step 1, the method further includes: The magnesium ingot, aluminum ingot, tin ingot, Mg-30RE master alloy, Mg-Y master alloy, Mg-Mn master alloy, Mg-Ca master alloy, Mg-Sn-Y master alloy and Mg-Sn-Ca master alloy are preheated at 100° C. to 120° C. for 30 to 60 minutes under argon protection.

5. The method for preparing the die-cast multi-element high-strength corrosion-resistant magnesium alloy according to claim 4, characterized in that: Calculated by mass percentage, the purity of the magnesium ingot, the purity of the aluminum ingot, and the purity of the tin ingot are all above 99.99%, and the impurity content of the Mg-30RE intermediate alloy, the impurity content of the Mg-Y intermediate alloy, the impurity content of the Mg-Mn intermediate alloy, the impurity content of the Mg-Ca intermediate alloy, the impurity content of the Mg-Sn-Y intermediate alloy, and the impurity content of the Mg-Sn-Ca intermediate alloy are all below 0.02%.

6. The method for preparing the die-cast multi-element high-strength corrosion-resistant magnesium alloy according to claim 5, characterized in that: In the step 1, the volume ratio of N2 to SF6 is 90:1 to 110:

1.

7. The method for preparing the die-cast multi-element high-strength corrosion-resistant magnesium alloy according to claim 6, characterized in that: In the step 3, after the tin ingot is completely melted, it is stirred by using a graphite stirring paddle, the stirring paddle speed is 150 to 300 rpm, and the stirring time is 5 to 10 minutes.

8. The method for preparing a die-cast multi-component high-strength and corrosion-resistant magnesium alloy according to any one of claims 2 to 7, characterized in that: In the step 4, dry argon gas is blown into the second alloy melt at 660° C. to 670° C. for refining.

9. The method for preparing the die-cast multi-element high-strength corrosion-resistant magnesium alloy according to claim 8, characterized in that: Before the step 4, the argon gas blown into the second alloy melt is pretreated by: After the argon gas is deoxygenated and dehydrated, it is heated at 500°C to obtain dry argon gas.

10. The method for preparing the die-cast multi-element high-strength corrosion-resistant magnesium alloy according to claim 9, characterized in that: In the step 5, the temperature of the die-casting mold is 240° C. to 300° C., the pouring temperature is 660° C. to 710° C., the boost pressure is 40 MPa to 50 MPa, and the holding time is 3 to 5 seconds.

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