Effects of rare earth neodymium (Nd) and heat treatment on anti-corrosion behaviors of the AZ80 magnesium alloy

The effect of rare earth neodymium (Nd) and heat treatment on the corrosion resistance of AZ80-xNd (x = 0, 0.5, and 1.0 wt.%) magnesium alloys was investigated. Compared to the as-cast AZ80 magnesium alloy, new rod-shaped Al3Nd phase and block-shaped Al2Nd phase were observed in AZ80-Nd alloy. Moreover, beta-Mg17Al12 phase becomes fine and discontinuous. The reduction of the beta-Mg17Al12 phase and the formation of the Al-Nd binary phase significantly reduced the corrosion rate of the AZ80-Nd alloy by suppressing micro-galvanic corrosion of the alloy. However, with increase in the the wt.% of Nd, the Al-Nd binary phase content increases, and the grain size become coarser, thereby lowering the corrosion resistance of the alloy. Therefore, the as-cast 0.5% Nd alloy with fine grain structure has a good corrosion resistance. After the solution treatment, the beta-Mg17Al12 phase and part of the Al-Nd binary phase were dissolved in the magnesium matrix, which facilitates the occurrence of corrosion. Therefore, the corrosion rate of solution treated alloys is higher than that of the as-cast alloys. After aging treatment, the beta-Mg17Al12 phase and Al-Nd binary phase are re-precipitated along the grain boundaries and within the grains, respectively. The fine and uniformly distributed beta-Mg17Al12 phase, rod-shaped Al3Nd phase and block-shaped Al2Nd phase effectively improve the corrosion resistance of the alloy, so that the corrosion rate of the aged alloy is the lowest. The electrochemical and immersion measurements revealed that the aged AZ80-0.5%Nd alloy had the best corrosion resistance.

Automated summary

The corrosion resistance of AZ80-xNd (x = 0, 0.5, and 1.0 wt.%) magnesium alloys is significantly affected by the rare earth neodymium (Nd) and heat treatment. The appropriate Nd content reduces the corrosion rate, but excessive Nd content decreases the corrosion resistance. The corrosion rate of solution treated alloys is higher than that of as-cast alloys, while the corrosion rate of aged alloys is the lowest. Rod-shaped Al3Nd phase and block-shaped Al2Nd phase effectively improve the corrosion resistance of the alloy.