Effect of interfacial reaction on mechanical behavior of SiCw/AZ91 magnesium matrix composites

SiCw/AZ91 magnesium matrix composites with acid aluminum phosphate (Al(PO₃)₃) binder and without binder were fabricated by a squeeze casting process. The interfacial microstructure, tensile properties and fracture behavior of the composites were studied. For the composites with no binders, the SiCw-AZ91 interfaces are very clean, whereas for the composites with acid phosphate binders, there exist fine, uniform and discrete interfacial MgO reaction products at the interface. The MgO particles are formed from the reaction between the binder and the molten Mg. There is a definite crystallographic orientation relationship between the reaction product MgO and SiCw, which leads to an interface with good lattice matching. The fine discrete interfacial MgO reaction products increase the whisker-matrix interfacial bonding strength, which is beneficial to the load transfer from the matrix to whisker, thus leading to improved Young's modulus and tensile strength of the composites with Al(PO₃)₃ binder over the composites without binder.