Microstructural correlation with tensile and creep properties of AZ91 alloy in three casting techniques

Abstract

The relationships among microstructure, tensile and creep behaviour of the AZ91 Mg alloy produced by three different casting techniques have been investigated. All the as-cast alloys consist of primary Mg (α-Mg) and β-Mg17Al12 phases. The volume fraction of β-Mg17Al12 phase is the highest in the gravity casting (GC), intermediate in the squeeze-casting (SC) and the lowest in the high-pressure die-casting (HPDC). The best tensile properties are exhibited by the SC alloy at all the temperatures employed in the present investigation owing to the presence of negligible porosity and relatively finer grain size. Fracture surfaces of the broken tensile specimens reveal the quasi-cleavage fracture. The best and the worst creep resistance are exhibited by the SC and HPDC alloys respectively with the GC alloy exhibiting the intermediate creep resistance. The inferior creep resistance of the HPDC alloy is attributed to the presence of a higher amount of porosity that allows easy crack initiation and growth during creep tests. On the contrary, the negligible porosity and continuous network of eutectic phase contributes to the superior creep resistance of the SC alloy.