The effects of grain size on the hot deformation and processing map for 7075 aluminum alloy

The effects of grain size on hot deformation and processing map of 7075 aluminum alloy were investigated using Gleeble-1500 test machine at 320–480 °C with strain rates from 0.001 to 1 s−1. The microstructural evolution observations of the alloy were carried out using ZESIS optical microscopy. The results showed that the flow stress increased with increasing strain rate and decreasing temperature. The flow stress of the alloy with coarse grains was higher than that of the alloy with fine grains. During hot-deformation, the alloy exhibited dynamic recovery at temperatures ranging from 320 to 440 °C and dynamic recrystallization at 480 °C. The processing maps for the alloy with different grain sizes were built at a strain of 0.6. It was found that the characteristics of the two processing maps were different. The instability deformation domain occurred at temperatures between 320 and 340 °C and at a strain rate of 0.18–1 s−1 for the alloy with coarse grains, but at temperatures between 380 and 420 °C and also at a strain rate of 0.18–1 s−1 for the alloy with fine grains. Based on the processing maps and microstructure observations, the optimum hot-working parameters were determined to be 480 °C at 0.1 s−1 for the coarse alloy and 480 °C at 0.01 s−1 for the fine alloy. The optimized hot working parameters of 7075 aluminum alloy with different grain size could be used in various hot working processes.