Effect of Rare Earth La on Microstructure, Hardness and Corrosion Resistance of A356 Aluminum Alloy

The effects of rare earth La on the microstructure, hardness, and corrosion resistance of A356 aluminum alloy were investigated by optical microscopys, scanning electron microscopy, energy dispersive spectroscopy and X-ray diffraction. The experimental results showed that with the addition of rare earth La, the microstructure was refined, and both Si phases and β-Al₅FeSi phases were transformed from long needle-like to short rod-like. The optimal microstructure and mechanical properties of the alloy were obtained when 0.6 wt% La was added. Compared with A356 aluminum alloy (88.36 HV), the hardness of A356 aluminum alloy modified with 0.6 wt% La (106.83 HV) was increased by 20.1%. The results of the immersion corrosion test and electrochemical experiments showed that the corrosion current density of A356 aluminum alloy modified with 0.6 wt% La (132.51 μA cm⁻²) was 24.8% lower than that of the matrix (176.24 μA cm⁻²), and the polarization resistance (668.56 Ω cm²) was 235.2% higher than that of the matrix (199.47 Ω cm²). This may be because the addition of rare earth La significantly reduced the cathode phases grain size in the corrosion micro-battery as well as the formation of intermetallic compounds containing rare earth La, leading to a decrease in the reaction rate of the cathode during corrosion.