Competition behavior of the strengthening effects in as-extruded AZ91 matrix: Influence of pre-existed Mg17Al12 phase

The AZ91 alloy containing (“AC”) and without (“AS”) Mg17Al12 phase were both subject to hot extrusion at 693 K with the extrusion ratio of 16:1. Results showed that the pre-existed Mg17Al12 phase in “AC” alloy led to finer grain size and lower intensity of basal plane texture as compared with “AS” alloy. Almost the same YS between “AC” and “AS” alloy indicated that the grain boundary and precipitation strengthening of “AC” alloy was balanced by the texture strengthening and solid solution strengthening of “AS” alloy. Nevertheless, the elongated Mg17Al12 phase along extrusion direction in “AC” alloy reduced its ultimate tensile strength as compared with “AS” alloy. Existence of SiCp led to a dispersive and uniform distribution of Mg17Al12 phase, which gave a full play on grain boundary and precipitation strengthening in “AC” composite. Unlike “AC” alloy, just the uniform and dispersive Mg17Al12 phase in “AC” composite contributed to the higher YS and UTS as compared with “AS” composite.