Effects of cell morphology and macrosegregation of directionally solidified Zn-rich Zn-Cu alloys on the resulting microhardness

摘要

Zn-1.0 wt.%Cu (monophasic) and Zn-2.2 wt.%Cu (hypoperitectic) alloys were investigated by transient di-rectional solidification, and the results include the cell spacing (λ_c) and correlation with the experimental tip cooling rate (T), macrosegregation, microhardness (HV) and the qualitative variation on η and e phases by XRD spectra. Only regions very close to the cooled casting surface of the Zn-2.2 wt.%Cu alloy casting, showed plate-like cells due to very high cooling rates (> 16 K/s) associated with a significant Cu enrichment. The Zn-2.2 wt.%Cu alloy exhibited HV values 2-3 times higher than those found for the Zn-1.0 wt.%Cu alloy. It is shown that the microhardness of the Zn-2.2 wt.%Cu alloy is directly influenced by both the inverse Cu segregation and by the morphologies of T| and e phases. Modified Hall-Petch equations are proposed relating HV to Kc for both alloys.