Microstructural Effects on the Formability of Rolled and Extruded Magnesium Sheet

Abstract

The automotive industry has become a major user of magnesium components. However, use of magnesium sheet products is quite limited, due to difficulties in producing cost effective components. Any sheet currently produced is formed at elevated temperatures, making magnesium parts relatively expensive. Knowledge of the microstructural effects on magnesium formability will help reduce the cost of these products. In this thesis, the microstructural factors that affect the formability of rolled and extruded magnesium sheet were compared. It was found that the degree of dynamic recrystallization was the factor that controlled elongation. Dynamic recrystallization produced a finer grain size, which resulted in a transition in deformation mechanism from dislocation slip to grain boundary sliding. Digital image correlation was used to study local stresses during tensile deformation, and to determine if magnesium satisfies Considere's criterion before failure. The results indicated that local stresses developed during deformation satisfied Considere's criterion, although the global strains were lower than the theoretical predictions.