Formation of intermetallic compounds in Mg–Ag–Al joints during diffusion bonding

In this study, we conducted the diffusion bonding of Mg and Al alloys using a 30-μm-thick pure silver foil interlayer at median temperatures between 390 and 490 °C. We obtained a multilayered structure across the Mg–Ag–Al joint: Mg/Mg(ss, Ag)/Mg3Ag/MgAg/Ag/Ag(ss, Al)/Ag2Al/Al. The silver diffusion barrier prevented the formation of brittle intermetallics between Mg and Al. Intermetallics identified at the joint interface include the more ductile types between Mg and Ag, e-Mg3Ag and β′-MgAg, and Ag and Al, δ-Ag2Al. As the bonding temperature increased, Ag2Al, followed by MgAg, favored the growth of Mg3Ag IMC layer. The shear strength of the joints increased with the rising bonding temperature to a maximum value of 11.8 MPa at 470 °C. Fracture failure in the joints mainly occurred in the Ag2Al layer. The formation mechanism for interfacial layers in the joints is believed to consist of four stages: (1) solid-solution formation, (2) Mg–Ag IMC formation, (3) Ag–Al IMC formation, and (4) growth of Mg–Ag and Ag–Al IMCs.