Studying the age hardening kinetics of A357 aluminum alloys through the Johnson–Mehl–Avrami theory

This paper demonstrates the application of the Johnson–Mehl–Avrami (JMA) theory to study the kinetics of the age hardening process in an A357 aluminum alloy. The precipitation hardening effect was studied at various times and temperatures. The outcomes show that the hardness can be improved via time and temperature changes. It is thus concluded that time and temperature are key variables in the precipitation hardening of the alloy. According to the results, solubilization at 823 K (550 °C) and then aging treatment at 453–463 K (180–190 °C) for 12–18 h is the optimum cycle to obtain the maximum hardness. The apparent activation energy of 40 kJ/mol was achieved through the kinetic studies. Based on the practical data, it is generally possible to estimate the hardness at a certain time and temperature by an appropriate equation. Furthermore, the maximum hardness and the time required to reach that maximum can be easily predicted through a suitable calculated relationship. Experiments by means of hardness measurement have been performed to provide the relevant information to validate the model. This paper aims to present the application of this simple modeling. The novelty of this paper is obtaining an equation that could be used to predict the hardness of an A357 alloy with a good agreement with the practical data.