Age hardening heat treatment behavior of as-cast Mg–Zn–Al alloys

Magnesium alloys have generated renewed interest as a light alloys; replacing some conventional structural materials for weight reduction in applications like aerospace, automotive and electronics industries. In interior components and powertrains, cast alloys are widely used and represent more than 99% of magnesium alloys used today, whereas only a few wrought products are used. Mostly in automotive applications, Mg-engine block can noticeably reduce the weight and consequently its fuel consumption and environmental impact. Due to solid-state precipitates, these alloys are strong in nature and are produced by an age-hardening heat treatment process. In the present work the age hardening behavior of the as cast Mg–Zn–Al alloys (ZA85 alloy) in the composition of 8 wt. %Zn, 5 wt. %Al has been investigated. Through the differential thermal analysis (DTA) studies, it has been found out that dissolution temperature of ternary eutectic precipitates is present in the alloy. Based on the DTA results, the as cast samples have been solutionised at 360 °C temperature for different intervals of time. Solutionising time has been optimized from the enthalpy values of un-dissolved precipitates. The solution treated samples have been then aged at temperature of 180° C for different time intervals. From the peak hardness values, the ageing conditions have been optimized.