Influence of Al Concentration and Zn Addition on the Corrosion Resistance of Rolled Mg–Al–(Zn)–Ca Magnesium Alloys

Abstract

The effects of Al concentration and Zn addition on the corrosion resistance of MgAl(Zn)Ca-based magnesium alloy rolled sheets were investigated. AXM (MgAlCa) alloys containing 1 mass% Ca and AZX (MgAlZnCa) alloys containing 1 mass% Ca plus 1 mass% Zn with the Al concentration adjusted to 6, 7, 8, 9, and 11 mass% were prepared. The corrosion behaviors of the alloys in a 5 mass% NaCl solution were evaluated by weight loss and the penetration depth. Electrochemical methods based on corrosion potential measurements and impedance spectroscopy was applied to monitor the corrosion behavior. The hydroxide film formed on the alloy surface was characterized by GDOES and SEM/EDS. The AXM alloy with an Al content of approximately 8 mass% exhibited minimum corrosion rate, whereas the AZX alloy showed the opposite result in the same concentration range of Al. This phenomenon was analyzed in terms of the Al concentration in the matrix (¡-phase), which was reduced by the precipitation of Mg 17 Al 12 (¢-phase) and the presence of Zn. The tendency of localized corrosion in high Al-containing AZX alloys was pointed out.

Effect of Al and Ca Elements on the Atmospheric Corrosion of Field-Exposed Mg–Al–Zn–Ca–Mn Magnesium Alloys

“…A similar trend has been observed in the corrosion of rolled Mg-Al-(Zn)-Ca-Mn alloys in 5% NaCl solutions. 37 Influence of Ca element on the atmospheric corrosion of Mg-Al alloys.-Liao and Hotta 18 pointed out several reasons for the lower corrosion resistance of AMX602 compared to AM60, such as the existence of cathodic Al 2 Ca precipitates, and the lower Al content in the AMX602 matrix due to the formation of Al 2 Ca. They also reported the finer grain size and dispersed Al 2 Ca were beneficial for corrosion resistance by comparing AMX602 samples with different microstructures.…”