Evolution of interfacial IMCs and mechanical performance of joints of Mg/Al dissimilar metals soldered by using Ga-coating protection

The soldering of Al/Mg dissimilar metals by using Sn–9Zn solder at a low temperature of 230 °C was investigated. A liquid gallium layer was coated on the faying surface of the base metals to avoid secondary oxidation and contact between Mg and Sn-based filler metal before soldering. The growth and distribution of intermetallic compounds (IMCs) at the interface of Mg/solder was focused on. The interface was composed of scattered large and dense small blocky IMC layers. The discontinuous Mg₂Sn layer was found to be the key factor dominating the mechanical performance of the joints. The highest shear strength of 38 MPa was reached at a reasonable holding time of ∼10 min. An over long holding time would cause the segregation of gallium which would deteriorate the water resistance of the joints.