Hyperbolic–sine constitutive model determined hot deformation mechanisms and workability response of Al–Zn/Cu and Al–Zn/SiC based composites

Abstract

The response to hot deformation of Al–Zn - based composites reinforced with copper (Al–Zn/6Cu) and silicon carbide (Al–Zn/8SiC) particles was investigated. The composites were fabricated using two-step stir-casting process, and subjected to hot–compression testing at various deformation temperatures ranging from 250 to 350 °C, strain rates of 0.01, to 10s–1, and a total strain of 0.5. The deformation data were modeled using hyperbolic–sine equations with microstructural analysis conducted for validation of deformation mechanisms. The results show that the Al–Zn/Cu reinforced composites exhibited relatively higher plastic flow resistance in comparison with the Al–Zn/8SiC composite and the Al–Zn alloy. The microstructures of the deformed composites revealed the presence of deformation bands, indicating the persistence of work hardening during the hot deformation process. The activation energies data obtained at peak stress for the Al–Zn/6Cu was 26.2% higher than that for self–diffusion of Aluminium alloy (QSD ∼142 kJ/mol), suggesting that dynamic recrystallization (DRX) was the governing softening mechanism; however, this was inconsistent with microstructural evidence which suggested a predominance of work hardening. The value of the QHW, for Al–Zn/8SiC composite was 20.7% lower than that for self–diffusion of Aluminium alloy, suggesting dynamic recovery (DRV)as the deformation governing mechanism which was upheld by the microstructures. The stress exponent (n) values exceeded 5 for all compositions, which suggested that work hardening predominates over both DRX and DRV, and this was supported by the microstructure of the hot deformed samples. The stress exponent was noted to yield a more consistent and reliable prediction of the deformation mechanism than the activation energy parameter.