Influence of bimodal grain size distribution on the corrosion resistance of Mg-4Li-3Al-1Zn (LAZ431)

This study describes the role of bimodal grain size distribution on the corrosion resistance of Mg-4Li-3Al-1Zn (LAZ431). The coarse-grained microstructure formed in the alloy after extrusion was compared with the bimodal grain size distribution observed in the alloy after additional annealing. The microstructure observations show that the extruded alloy, as well as the one after subsequent annealing, were composed of alpha(Mg), MgZn2, coarse AlMn-rich precipitations, and nanosized AlLi, Mg17Al12 and Li2MgAl. The annealing caused microstructure transformation and triggered anomalous and inhomogeneous grain growth of the alloy, which increased the ratio of cathodic grain interiors to anodic high-angle grain boundaries. This decreased the corrosion resistance of the annealed alloy in chloride containing solution.The results of this work also show that the precipitations play only minor role in corrosion behavior of both alloys, and the major corrosion mechanism occurred between high-angle grain boundaries and grain interiors. (C) 2021 The Author(s). Published by Elsevier B.V.