Effects of high-density pulse current on mechanical properties and microstructure in a rolled Mg-9.3Li-1.79Al-1.61Zn alloy

The ultimate tensile strength of 209 MPa and the elongation to failure of 24% were demonstrated in as-rolled Mg-9.3Li-1.79Al-1.61Zn (designated as LAZ922) alloy sheets. Variation in true stress with true strain showed that stress decreases and elongation to failure increases under high density pulsed current. The stresses at the current density of 1.44×103 and 2.11×103 A/mm2 decreased by 57% and 82%, respectively, relative to the stress without a current. The elongations to failure at above current density were 33.2% and 78%. These were somewhat larger than the elongation to failure of 24% without a current. The imposed current promoted the appearance of some equiaxed grains within the elongated grains in the gauge section and induced partial dynamic recrystallization. The formation of needle grains near the fracture site at the current density of 2.11×103 A/mm2 can be attributed to the occurrence of new grain boundaries caused by the lattice expansion due to an increase in temperature. Dislocation studies revealed that, as the current density increases, the structure evolution such as the formation of tangled dislocations, the formation of dislocation walls at the subgrain boundary, and the disappearance of dislocations within the subgrain takes place. New models of dislocation density and number of dislocations inside the grain in the presence of current were established. The changing trend of the model prediction was consistent with experimental results.