Microstructure and corrosion resistance of a duplex structured Mg–7.5Li–3Al–1Zn

Abstract

This study describes the corrosion resistance of extruded, and extruded with post-processing annealing, Mg–7.5Li–3Al–1Zn alloys. The results demonstrate that extrusion at 350 °C with an extrusion speed 0.5 s−1 does not lead to the full recrystallization of the alloy, and the material still exhibits a dendritic microstructure. The post-processing annealing triggers the microstructure transformation, and the relative composition of the alloy changes. The ratio of β(Li) to α(Mg) in the extruded alloy was 29–71%; after annealing amount of β(Li) increased, and the ratio of β(Li) to α(Mg) in the annealed alloy was 35–65%. Corrosion testing shows that in 3.5 wt% NaCl the extruded alloys immediately undergo strong dissolution. As a result of the subsequent annealing, an improvement of corrosion resistance is observed. The higher amount of β(Li) in the annealed alloy reduces the area ratio of cathodic to anodic sites of corrosion, and this makes the annealed alloy more resistive under the analyzed conditions.

Keywords

• Magnesium–Lithium corrosion
• Extrusion
• Annealing