Creep deformation study of AZ91-based magnesium alloys

Abstract

In order to improve vehicle fuel efficiency and reduce carbon emissions in the environment, the demand for lightweight materials has increased day by day in the transportation industry. Magnesium (Mg) and alloys serve as the exceptionally lightest structural materials available compared to Aluminium, Titanium, and Steel. Amongst the available, AZ91 (Mg-Al-Zn) alloy is the most widely used Mg alloy in the automotive industry owing to its excellent die-castability and adequate mechanical properties at room temperature. However, the poor creep resistance limits its service temperatures above 120 °C, making it incompetent for major powertrain applications. The α-Mg (Mg-Al solid solution) and β-Mg17Al12 are the main phases observed in the microstructure of AZ91 alloy. The latter appears to be thermally unstable and starts partially dissolving above the temperature of 120-125 °C. Also, the die casting of the alloy involves porosity and blow holes, which further affects the creep performance of the alloys adversely.