Assessing the implication of homogenization and hard-plate hot forging induced microstructural evolution on corrosion response of a cast Mg-2Zn-1Nd alloy

Abstract

This work investigates the effect of homogenization and subsequent hard-plate hot forging induced microstructural variations on the corrosion response of Mg-2Zn-1Nd alloy against the as-cast condition. The electrochemical studies have revealed that the cast specimen exhibits poor corrosion performance due to the presence of interconnected networks of Mg12Nd phase along the grain boundaries. Consequently, micro-galvanic corrosion takes place and the overall corrosion response is deteriorated. Moreover, the product film thickness is higher in this case implying the presence of higher growth stresses which leads to the formation of cracks in the film. This subsequently results in the development of a highly non-protective film over the cast specimen, as evident from the topography of corrosion product film observed through atomic force microscopy. Post homogenization treatment, the networks of Mg12Nd phase are partially disrupted, resulting in a considerable improvement in corrosion performance. The networks are completely disrupted and a further decrease in the secondary phase fraction is observed in the forged specimen, resulting in a lower extent of galvanic corrosion. Additionally, the presence of fine grains in this specimen promotes the rapid development of a product film, resulting in a superior corrosion performance of the forged specimen. Most importantly, the growth stresses in this case is relieved through the higher grain boundary density, which limits the formation of cracks in the passive film. Besides, the basal texture minimizes the surface energy and reduces the dissolution rate of the forged specimen, which further enhance the corrosion resistance of forged specimen in comparison to the cast or homogenized conditions.