Evolution of interfacial structure and fracture behavior in ZL702A/SUS304 compound castings with different surface treatments

ZL702A/SUS304 bimetallic castings were prepared by compound casting with different surface pretreatments , in terms of hot-dip aluminizing method and surface modifier + hot-dip aluminizing method. The bimetal interface prepared with no surface modifier was consisted of a tongue-like AlFeSi compound layer and an oxidation layer containing numerous micro-voids, accompanied with aluminum oxide curves near the interface which were overlapped with eutectic Si along grain boundaries in ZL702A substrate. In the case of surface modifier + hot-dip aluminizing, the incompact oxidation layer was almost disappeared at the interface, with no other observable microstructural difference relative to its counterpart. In consequence, the additional surface modifier greatly increased the integrity of the bimetal interface and leaded to a significant improvement of shear strength to ∼77.9 MPa, in comparison to its counterpart with no surface modifier of ∼21.7 MPa. Fracture during shear test in the bimetal with no surface modifier was dominantly occurred along the fragile oxidation layer. While in the bimetal with surface modifier, fracture was mainly occurred in the more compact and ductile ZL702A substrate, accounting for the increase of its shear strength. This work provides fresh ideas for tailoring the interfacial microstructure and improving the bonding properties of Al/steel bimetals by compound casting.