Effects of heat treatment on microstructure, mechanical properties and damping capacity of Mg-Zn-Y-Zr alloy

The influences of solution and ageing treatment on the microstructure, mechanical properties, and damping capacity of as-cast Mg-2%Zn-1%Y-0.6%Zr alloy were investigated. The results indicate that the solution treatment at 525 °C for 4 h (T4 treatment) could obviously enhance the tensile strength. This mainly contributes to the dissolution of the net-like interdendritic eutectic structures and the transformation of I-phase into W-phase with unique structure characteristic. A subsequent ageing treatment (T6 treatment) results in the precipitation of W, β1' and β2' phases, which helps improve the ultimate tensile strength, yield strength and elongation from 174 MPa, 125 Mpa and 11.2% in as-cast alloy to 238 MPa, 147 MPa and 12.8%. The damping capacity of the Mg-Zn-Y-Zr alloy decreases dramatically after heat treatment and the damping behavior can be explained with the G-L dislocation theory. The forming of precipitates during solution-ageing treatment makes more phases and interfaces generate in the alloys. And the mobile dislocation densities in the heat-treated alloy hardly change as severe accumulation and entanglement of dislocation generate at the interface between W-phase and the α-Mg matrix. Therefore, the internal friction of Mg-2%Zn-1%Y-0.6%Zr alloy deteriorates accordingly with the increasing amount of strong pinning points on dislocations.