Development of non-flammable high strength AZ91+Ca alloys via liquid forging and extrusion

Non-flammable high strength magnesium alloys were developed from AZ91 alloy mainly for the weight reduction in industrial applications. Calcium of 2,4 and 6 wt.% was added and the ignition point was tested to study the flammability. Liquid forging and hot extrusion were applied to these alloys in order to enhance the mechanical properties. The microstructure, hardness and tensile properties were investigated to study the effects of calcium additions and different manufacturing processes. The results showed that calcium additions significantly improved the non-flammability, but mechanical properties of the gravity cast samples were degraded due to large amounts of Al2Ca at grain boundaries. After liquid forging and extrusion process, an increase of the mechanical properties was observed in the non-flammable magnesium alloys. The enhancement of properties was mainly contributed by the refined microstructure, redistribution of second phase and less porosity defects. Among all the tested alloys, AZ91 + 2% Ca prepared by liquid forging + extrusion demonstrated the optimal balance of high ignition point and excellent strength and ductility. 4% Ca addition further improves the ignition resistance and tensile strength of AZ91 alloy. The advantages of the manufacturing process combining liquid forging and hot extrusion were demonstrated to achieve improved mechanical properties for non-flammable magnesium alloys. (C) 2016 Elsevier Ltd. All rights reserved.