Effect of Al contents on microstructures, tensile and creep properties of Mg–Al–Sr–Ca alloy

Abstract

Microstructures, tensile and creep properties of Mg–(4–7)Al–1Sr–1Ca (AJC411–711) alloys have been investigated. The as-cast microstructure of Mg–(4–7)Al–1Sr–1Ca alloys consists of the α-Mg matrix and grain boundary intermetallics. In the alloy with 4% of Al addition (AJC411) thin lamellar eutectic Mg 2Ca, coarse eutectic (Mg, Al) 2Ca and a bulky ternary Mg–Al–Sr phase are observed at grain boundaries. With increase of Al content, the volume fraction of the Mg 2Ca and Mg–Al–Sr phase decreases, meanwhile that of the coarse (Mg, Al) 2Ca phase increases. A 7% of Al addition leads to the formation of another thin lamellar eutectic Al 4Sr at grain boundaries besides eutectic (Mg, Al) 2Ca. The bulky ternary phase and Mg 2Ca phase cannot be found in Mg–7Al–1Sr–1Ca (AJC711) alloy. Both strength and ductility increase with the increase of Al concentration in the alloys studied at ambient and elevated temperatures of 175 and 200 °C. At the conditions of 175 °C/70 MPa and 200 °C/70 MPa, the alloys Mg–6Al–1Sr–1Ca (AJC611) and Mg–5Al–1Sr–1Ca (AJC511) show best creep resistance among prepared alloys, respectively. Higher Al concentration results in remarkable reduction of creep properties.