Influence of annealing on microstructures,mechanical and creep properties of Mg–4Al–2Sr alloy

Abstract

Microstructures, mechanical properties and creep resistance of the Mg–4Al–2Sr (AJ42) alloy were investigated both in the as cast condition and after annealing heat treatment at 400°C for 5–200 h. The as cast microstructure of AJ42 alloy consists of dendritic α -Mg and intermetallic compounds, Al₄ Sr and a bulky type ternary Mg–Al–Sr phase, distributing at grain boundaries. Annealing the alloy at 400°C results in spheroidisation of eutectic Al₄ Sr and breaking up of the continuous grain boundary network existing in the as cast microstructure before annealing gradually. The hardness and tensile properties do not show obvious changes after annealing at 400°C for 200 h. The as cast AJ42 shows a high creep resistance at 175°C/70 MPa in comparison with that of commercial Mg–Al based alloys, however, the creep resistance of the alloy is significantly decreased after annealed at 400°C owing to morphology modification of the grain boundary interphases.