Microstructural evolution and mechanical properties of a Mg-Gd-Y alloy processed by impact forging

A multi-direction impact forging (MDIF) has been applied to a solutionized Mg-Gd-Y-Zr alloy in this work. An inhomogeneous microstructure, mostly fine grains, some twins and a few of coarse deformed grains were achieved with a weak and non-basal texture after 50 forging passes. Due to retarded DRX behavior by RE solute drag effect and the sharp drop of forging temperature, the alloy did not obtain a full DRX microstructure until 100 forging passes. During MDIF process, density of extension twins initially were induced in microstructure, which effectively refined the coarse grains by dividing and intersecting each other. In turn, those twining regions provided nucleation sites for DRX, and a continuous dynamic recrystallization converted most of the twin-matrix laminates to fine equi-axial grains. The ultimate tensile strength and elongation to failure of GW94 alloy were continuously improved during MDIF process, from less than 200 MPa and 2% of the initial solutionized specimen to more than 300 MPa and 7% of the one by 50 forging passes respectively.