Fluxless soldering of 7034 aluminium in air using protective liquid Ga coatings

Fine-grained 7034 aluminium alloys were soldered with Zn–5Al filler metals, using liquid Ga as protective coatings to remove oxide films of the base and filler metals and prevent secondary oxidation. Holding times and coating modes were adjusted by experiments. Applying the Ga coating on both the base and filler metals caused the Ga enrichment in the α-Al particles and the formation of Mg₂Ga₅ intermetallic compound at the bonding interface, deteriorating joint mechanical performance. Ga enrichment was prevented by applying the coating on the filler metal alone, which avoided the early contact of Ga with Al substrate and reduced the mass of Ga in the joint. The tensile strength increased significantly to 159∼185 MPa with a sufficient holding time.