The effects of Er addition on the microstructure and properties of an in situ nano ZrB2-reinforced A356.2 composite

In this study, the effects of Er addition on the microstructure and properties of in situ nano A356-3 wt%ZrB2 composites were investigated. The A356-3 wt%ZrB2 composite was prepared by an in situ reaction between K2ZrF6 and KBF4 salts, which were added in the proper stoichiometric ratio to form ZrB2 in the A356.2 alloy melt at 1123 K(850 °C). The addition of Er could modify the coarse lamellar eutectic Si particles into fine fibrous particles and refine the second dendrite arm spacing (SDAS) of the grains simultaneously. Furthermore, the Er also influenced the distribution and size of the ZrB2 particles by homogenizing the distribution of the nanoparticles and reducing their size. Tensile testing showed that the ultimate tensile strength (UTS), yield strength (YS) and elongation increased to 325 MPa, 250MPa and 13.65%, respectively, due to the homogeneous distribution of the nanoparticles, the refinement of the SDAS of the α-Al grains and the modification of the eutectic Si particles upon increasing the Er content to 0.05 wt% combined with T6 heat treatment.