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

摘要

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 alpha-Mg matrix and grain boundary intermetallics. In the alloy with 4 percent 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 percent 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 deg C. At the conditions of 175 deg C/70 MPa and 200 deg 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.