Microstructure and corrosion behavior of a hot-rolled pure Mg after annealing at various temperatures

Abstract

The microstructure and corrosion behavior of a hot-rolled pure Mg in the rolled state and after annealing at various temperatures was studied in this paper. It was found that the hot-rolled pure Mg after annealing at 250 °C, 350 °C, 400 °C, 500 °C and 550 °C showed homogeneous microstructures and the presence of a partially recrystallised tissue in hot rolled pure Mg. Corrosion of annealed Mg mainly occurred at grain boundaries, which stemmed from the relatively higher energy and chemical activation on the grain boundaries. Initial corrosion sites were provided by different proportions of High angle grain boundaries (HAGBs). The corrosion rate tends to increase and then decrease with increasing grain size. The Mg annealed at 450 °C showed a non-uniformed microstructure, with a lower fraction of the recrystallization grains and higher fraction of HAGBs, leaving to the severe localized corrosion and the highest corrosion rates. Corrosion rate measurement indicated that there existed a curvilinear relationship between the corrosion rate and grain size.