Aging Hardening Behavior of Zn-22Al Alloy

The effects of aging treatment on the microstructure and mechanical properties of Zn-22Al alloy were investigated by means of Vickers hardness test, scanning electron microscopy(SEM), transmission electron microscopy(TEM)and energy dispersive spectroscopy (EDS).The results show that, the microstructure of Zn-22Al alloy is formed by equiaxed dendrites when the solution treatment temperature is lower than the eutectoid transition point.The dendrites consist of the equilibrium Al-rich α₁ phase and zinc-rich η phase.In the subsequent aging process, the morphology of the dendrites does not change significantly, and the hardness of the alloy decreases slowly.When the solution treatment temperature is above the eutectoid transition point, the microstructure of Zn-22Al alloy is formed by granular fine grains containing the metastable zinc-rich α₂ phase.In the subsequent aging process, the grain of alloy coarsen.The metastable zinc-rich α₂ phase is decomposed into the equilibrium Al-rich α₁ phase and zinc-rich η phase, and the aging hardening phenomenon of the alloy appears.