Effects of Heat Treatment on Microstructure, Mechanical Properties and Corrosion Resistance of Al-Si-Mg-3%Cr Alloy

Al-Si-Mg-3%Cr alloy was prepared with vacuum electromagnetic induction melting furnace. Thermo-Calc software was used to perform thermodynamic simulation. The microstructure of the alloy under different heat treatment conditions were characterized by SEM, EDS, and other test methods and its mechanical properties were tested. The corrosion resistance of the alloy was tested by mass loss method and electrochemical method. The results show that the main phases of the Al-Si-Mg-3%Cr alloy include alpha-Al, eutectic Si, (Al+Si) eutectic, Cr rich phase (Al13Cr4Si4, beta-Al (Cr, Fe) Si), Fe rich phase (beta-Al5FeSi and pi-AlSiMgFe) and Mg2Si. In the structure of heat-treated alloy, the eutectic Si becomes smaller in size and spheroidized in form, the zone of eutectic structure becomes narrow, and the fine Al13Cr4Si4 and beta-Al(Cr,Fe)Si phase are dispersed around eutectic Si. All play positive roles in improving the mechanical properties of the alloy after heat treatment. The corrosion test results show that compared with the case of the as-cast alloy, the average corrosion rate of the heat-treated alloy decreases, an obvious passivation zone exists in the polarization curve, and the capacitive arc in impedance becomes larger. It is indicated that heat treatment can improve the corrosion resistance of the alloy, especially T6 process (535 degrees C/6 h+160 degrees C/26 h) can lead to the optimum mechanical properties and corrosion resistance.