Effects of in-situ ZrB2 particle on grain refinement of ZrB2/AZ91D magnesium matrix composite

In-situ ZrB2/AZ91D magnesium matrix composite was successfully synthesized with Al/K2ZrF6+NH4BF4 by means of Direct Melt Reaction. The fabricated ZrB2 /AZ91D magnesium matrix composite through direct melt mixing method was investigated. Results from X-ray diffraction (XRD) and energy dispersive X-ray spectroscopy (EDS) confirmed the existence of ZrB2 particles in the AZ91D alloy, and most ZrB2 particles were in the size range of just several microns, some even to 100 nm. The cast specimens were studied through corrosion testing and heat treatment. The average grain size of AZ91D decreased markedly from about 250 μm to 50 μm. In addition, the shape and size of the β-Mg17Al12 phase as well as the morphologies of primary α-Mg in the magnesium matrix composite were greatly changed. The network structure of the β-Mg17Al12 phase was broken into small blocks and the size of α-Mg decreased significantly.