Exploring a balance between strength and ductility of hexagonal BN nanoplatelet reinforced ZK61 magnesium composite

The practical applications of magnesium (Mg) alloys are usually beset by their relatively low strength and limited ductility. Herein we attempt to fabricate hexagonal BN nanoplatelet (BNNP) reinforced ZK61 magnesium composites using a combination of spark plasma sintering and friction stir processing. The resulting composites exhibit microstructural characteristics of homogeneous dispersion of BNNP in Mg matrix with refined equiaxed grains and (0002) basal texture roughly surrounding the pin column surface. Transmission electron microscopy observation illustrates that trace amounts of Mg3N2 and MgB2 form at BNNP-Mg interface, in which Mg3N2 locates at the basal plane of a BNNP and MgB2 grows at its open edge. The spatial distribution of Mg3N2 and MgB2 facilitates interfacial wetting and stronger BNNP-Mg interface in such a way that interfacial products act as anchors bonding between them. In comparison with monolithic ZK61 alloy, the BNNP/ZK61 composites display simultaneous improvements in yield strength, hardness and ductility, achieving good strength-ductility balance. This research is expected to shed some light on BNNP potentials for designing and producing magnesium composites with high strength and good ductility.