Role of Micro-Alloyed Sm, La, and Ce in Affecting the Microstructures and Corrosion Behaviors of the As-Cast Mg-6Al-1Sn Alloy

The roles of light Re (Sm, La, and Ce) on microstructures and corrosion behaviors of the AT61 alloy were investigated. The results showed that Al₁₁Sm₃, Al₂Sm, Al₁₁La₃, and Al₄Ce precipitated after adding 1%Sm, La, and Ce separately, which had different effects on the corrosion resistance to AT61 alloy. The hydrogen evolution, weight loss rate, self-corrosion current density, and polarization resistance of AT61-1Sm alloy were 0.29 mL cm⁻², 0.48 mg cm⁻² day⁻¹, 7.228 μ A cm⁻², and 4405.220 Ω cm⁻², respectively. The significant improvement of corrosion resistance by 1% Sm was mainly due to the great reduction of Mg₁₇Al₁₂, the inhibition of the corrosion by uniform distribution of Al₁₁Sm₃ along the grain boundary, and the dense Al₂O₃ protective film caused by Al₂Sm. Compared to AT61, the corrosion resistance of AT61-1Ce has also been improved because the Al₄Ce is cross-distributed and tightly bound to the Mg matrix, acting as a barrier during corrosion and inhibiting the progression of corrosion. However, the corrosion resistance of AT61-La decreased because the Al₁₁La₃ produced a strong galvanic couple with the Mg matrix during the corrosion process, which was easy to detach and form corrosion pits, resulting in accelerating the corrosion.