Microstructural characteristics, mechanical and corrosion properties of a low-alloyed Mg alloy after different deformation processing

Abstract

Abstract. In the evolution of characteristics in Mg alloys, the combined influence of grain refinement by severe plastic deformation (SPD) and alloying elements usually plays a crucial role. Rare earth elements (Y, Gd, and Nd) in combination with Zn have a substantial impact on Mg characteristics in various compositions. In this study, a new dilute extruded Mg-Zn-Gd-Y-Nd alloy was exposed to 5 passes of equal channel angular pressing (ECAP), in a die with a 90° channel angle following route Bc. The initial deformation temperature was 300°C, and it dropped to 200°C with a 25°C step until the fifth pass. Initial and deformed samples were subjected to hardness testing, optical and scanning electron microscopy (SEM) examinations and corrosion tests. After the fifth run of ECAP at 200°C, necklaces of fine recrystallized grains along grain boundaries of elongated unrecrystallized grains in extruded samples transformed to an ultrafine grained microstructure. SEM images reveal the presence of very fine nanoscale dynamic recrystallization (DRX) nuclei in the context of the ECAPed alloy. Furthermore, measures of hardness show the increase in hardness from the starting state to the fifth pass of ECAP. The increase in hardness was caused by dynamic recrystallization, which resulted in a higher percentage of freshly produced grains and grain boundaries. Furthermore, the inclusion of rare earth elements increased grain refinement and controlled the rate of dynamic recrystallization (DRX) during ECAP. On the other hand, severe plastic deformation cause changes in the density and distribution of grain boundaries and defects, which affect the corrosion behavior of magnesium alloys. Additionally, in comparison to the as cast condition the extruded-annealed, ECAPed and as-extruded samples have better corrosion resistance, respectively. It can be concluded that grain refinement has positive effect on decreasing the corrosion rate while homogenization of the extruded microstructure is more effective.