Effect of grain diameter on the work-hardening characteristics of Zn-1 wt.% Cu alloy during phase transformation

Stress-strain characteristics of slowly cooled Zn-1 wt.% Cu alloy specimens with different grain diameters have been studied in the temperature range from 453 to 573 K. The work-hardening parameters; coefficient of work-hardening, χp, yield stress, σy, and fracture stress, σf of the investigated specimens were found to decrease in a non-monotonic behaviour with increasing the deformation temperature. Two decreasing stages were observed before and after the transformation temperature 513 K. The rate of change of these parameters as well as the strain hardening exponent n (= d lnσ/d lnε) were investigated as function of deformation temperature. They showed two different behaviours before and after the transformation temperature. The effect of grain diameter on the above work-hardening parameters were also taken into consideration. The work-hardening parameters were found to increase with increasing grain diameter while the strain hardening exponent n is decreased. The obtained results were interpreted on the basis of the coarsening of ε-phase at the early stages of the first temperature range while the second stage referred to the thermal agitation of dislocation motion. The two observed temperature regions below and above 513 K may characterize a point of dislocation intersection mechanisms activated with ∼0.2 eV for the two regions. The microstructure of the samples under investigation was examined by optical microscopy (OM).