High-strength joining of 6063Al alloys by an Zn–Sn hypereutectic interlayer in air based on liquid and solid phase diffusion

A high strength joint obtained at relatively low temperature and pressure by diffusion bonding has always been a challenge for manufacturing of aluminum alloy heat sinks. In this work, joining of 6063Al alloys was performed by a novel liquid and solid phase diffusion bonding method with an Zn–30Sn hypereutectic interlayer. It was achieved at a heating temperature of 360 °C and a pressure of 1 MPa. A 6063Al joint bonded was composed mainly of Zn–Al eutectoid phases and had a higher strength than the base metal. During the diffusion bonding process, the joint was constituted of Sn–Zn eutectic phases and η-Zn phases at initial diffusion stage. The proportion of Sn–Zn eutectic phases gradually decreased and Zn–Al eutectoid phases increased in a joint through inter-diffusion between base metal and interlayer with increasing of holding time. The η-Zn phases finally transformed into Zn–Al eutectoid phases with depleting of Sn–Zn eutectic phases, in which only 0.02 wt% Sn element was remained in the joint. The liquid and solid phase diffusion mechanisms were revealed. The penetration of Sn to the grain boundary of Al alloy happened under an assistance of the Zn diffusion. The Al originated from base metal interdiffused with η-Zn phases, forming Zn–Al eutectoid phases.