Magnesium alloy is currently the lightest metal structural material. It has excellent specific stiffness and specific strength, good dimensional stability, high electromagnetic shielding and excellent cutting processability. It is widely used in the aviation industry, automobile and motorcycle industry. applications are gradually increasing. At present, more than 70% of the world's magnesium alloy parts are used in the automobile industry. If the weight of the car itself is reduced by 100kg, the car will save about 0.5L of fuel for 100km of travel. Each 1L of fuel saved can reduce CO2 emissions by 2.5g. The total annual CO2 emissions are reduced by more than 30%. It can be seen that the research and development of magnesium alloys has an important impact on improving the environment and saving energy. Studies believe that rare earths can purify magnesium alloy melts, improve the casting properties of the alloy, refine the alloy microstructure, and improve its oxidation resistance. Compared with other rare earth elements, rare earth Sm has a special rhombic structure, and its solid solubility in magnesium can reach 5.7wt%. Currently, there are few research documents related to Mg-Al alloys containing Sm. In addition, AZ61 alloy has both high mechanical properties and excellent casting properties. Based on the above reasons, this paper studies the effect of rare earth Sm on the microstructure of AZ61 alloy.
The raw materials used in the experiment are magnesium ingots (purity 99.95wt%), aluminum ingots (purity 99.98wt%), zinc (analytically pure), and magnesium-samarium master alloy. All raw materials must be dried before smelting. The chemical composition of the alloy is (mass fraction, %): 6Al, 1Zn, and the balance is Mg. The contents of Sm are 0,0.5,1,1.5,2 respectively. The alloy is smelted in an electromagnetic induction melting furnace, and SF60.2% (volume fraction) + CO2 is used to protect the alloy melt during smelting. When the melt temperature reaches 690°C, the alloy liquid is poured into a metal mold preheated at 250°C. Cover the metal sample with MgO powder and place it in a box furnace for solid solution (420℃×20h) and aging (200℃×10h) treatment.
By adding 0.5% to 2.0% Sm rare earths to AZ61 alloy, the alloy's microstructure in the as-cast and aged state is significantly refined. Within the scope of the study, after adding Sm to the alloy, a dispersed high-melting point Al2Sm compound phase was formed in the alloy, and the amount of Mg17Al12 was significantly reduced. Mismatch calculations and TEM observations showed that Al2Sm can serve as an effective nucleation core for α-Mg. This This is an important reason why the structure of AZ61 alloy can be significantly refined after the addition of Sm.
