Ultrasonic-assisted fluxless reactive bonding of Mg/Al dissimilar alloy using Zn–Al solder in air

An ultrasonic-assisted reactive brazing method, without flux and conducted in air, was developed to braze Mg/Al dissimilar alloys. By using pre-coated Zn-Al solders on the Al sheet and a short-time ultrasonic (3 s) assistance, the Mg/Al dissimilar sheets were successfully brazed at a low temperature (340 degrees C). The effect of Al content of the solder on the shear strength was investigated based on the analysis of the microstructure and the fracture behaviour of the brazed joint. The results indicated that the microstructure and the shear strength of the ultrasonic-assisted brazed joint were significantly affected by Al content in Zn-Al solders. Increasing Al content in Zn-Al solder prevented the joint from forming the continuous brittle MgZn2 layer. The maximum shear strength of 110.5 MPa was obtained when Zn-15Al solder was used, because the joint possessed the optimum microstructure of the soft (Al, Zn) eutectoid matrix with the MgZn2 dispersed particles.