Study on microstructure and performance of transient liquid phase bonding of Cu/Al with Al-based interlayers

Transient liquid phase bonding of aluminium and copper (without interlayer, Al-11Si-4Cu-2Mg and Al-4.5Si-2Cu-1Mg foil) were carried out in sandwich-like coupon assemblies under different temperature in vacuum environment. The interfacial structure and composition of the bonding interface were investigated. The bonding strength and resistivity were tested. Two layers of compounds were formed on the interface in all the bonding joints. The main difference in the joints using different interlayer was the microstructure of the Al2Cu and Al2Cu/Al interfacial structures. The interface of the joint without interlayer consisted mainly of Al-Cu eutectic (Al2Cu + Al) near Al side and the Al2Cu phase presented a continuous reticular structure. In the joints using interlayer, the formation of Al2Cu can be significantly inhibited. The shear strengths of the joints using Al-11Si-4Cu-2Mg foil at 575 °C reached to 77 MPa which was close to the shear strength of Al base metal. The resistivity of TLP joint was near the theoretical resistivity and then it has good conductivity.