Characterization of Zn–Al based brazing filler for steel/aluminum dissimilar joints

This study investigates the development of a Zn-xAl-3Cu brazing filler specifically formulated for dissimilar joints between steel and aluminum. The research highlights the influence of aluminum content on the solidification characteristics, microstructural features, and mechanical properties of the resulting steel/aluminum joints. It was found that when the aluminum content does not exceed 12 wt%, a filler alloy can be produced with a fully liquid phase temperature below 450 °C, thereby facilitating a lower brazing temperature. An increase in aluminum content was observed to decrease the contact angles of the alloy with aluminum base metals, while the contact angles increased with steel base metals. The solidification structure of the filler alloy comprises proeutectic dendrites, eutectics, and fine α + η eutectoids, with a higher aluminum content resulting in an increased proportion of α + η eutectoids. The filler alloy promotes intergranular penetration of Zn into the aluminum base metal, while at the interface with the steel base, it forms layered Fe 2 Al 5 Zn 0.4 and a minor quantity of discontinuous FeZn 10 intermetallic compounds (IMC). Notably, the filler alloy containing 12 wt% Al exhibits the highest hardness; however, the maximum tensile strength is observed in the alloy with 10 wt% Al. This discrepancy is attributed to the fractured structure of the IMC layer in the 12 wt% Al alloy, which leads to preferential crack propagation from the IMC layer.