Weibull analysis of effect of T6 heat treatment on fracture strength of AM60B magnesium alloy

The effect of T6 heat treatment on the fracture strength and reliability of AM60B alloy was studied. The tensile specimens were poured at three different temperatures of 670, 685 and 700 °C for different holding times of 5, 10 and 15 min. The fluidity test was also conducted to determine the fluidity length under different pouring temperatures and holding times. According to the results, the optimum pouring temperature and holding time were determined as 685 °C and 10 min, respectively. SEM fractography of the tensile specimens reveals that the entrained oxides and oxide-related porosities are the main factors responsible for the reduction of fracture strength under the non-optimal casting conditions. The Weibull statistical approach was used to quantify the scatter of fracture strength in as-cast and heat-treated conditions. For this purpose, T6 schedule was applied to the specimens prepared under the optimal casting condition. It is found that, despite minor effect on the average fracture strength, T6 heat treatment improves the reliability of castings, where the Weibull modulus is increased by 75%. According to the microstructural and fractography observations, this improvement is related to the evolution of more uniform microstructure and the elimination of coarse brittle β-particles in heat-treated samples.