Microhardness and microstructure characteristics of AZ91 magnesium alloy under different cooling rate conditions

The objective of the present work is to investigate the influence of aging time and cooling rate conditions on the microstructure and mechanical properties of AZ91 magnesium alloy. After solution heat treatment condition, samples were isothermally aged at 200 °C for various times ranging from 4 to 192 h followed by cooling in two different media: water and furnace which resulted in cooling rates of 20 °C s−1 (fast cooling rate) and 0.1 °C s−1 (slow cooling rate) respectively. The results revealed that the hardness values for the faster cooling rate are higher than that of the smaller cooling rate. Maximum hardness has been achieved after aging for 24 h for both two cooling conditions. The influence of both continuous and discontinuous precipitates of β-phase, as a function of aging time and cooling rate, on the age-hardening response has been elaborated. An artificial neural network (ANN) model was applied to simulate and predict the hardness profile of the investigated alloy. The experimental data were confirmed by the calculated results.