Effects of Alloying Copper and Silicon on the Bondability of Dissimilar Metal Joints of Aluminum Alloys to Steel

Abstract

The effects of Cu and Si in aluminum alloys on the joint properties of Aluminum alloys/steels were evaluated by correlating the interfacial microstructures with the joint strength using diffusion bonding. It was found that joint strength was improved by adding Cu to aluminum alloys, because Cu suppressed formation and growth of a reaction layer. Moreover, the effect was much larger by Cu and Si combined addition. The fracture for the joints with higher strength occurred within the base aluminum alloys. As a reaction layer is thicker, the fracture mode was changed from an interfacial fracture to an aluminum alloy matrix and a reaction layer fracture, regardless of containing copper. For all investigated alloys, the highest joint strength was obtained in a certain value of reaction layer thickness, in particular, the optimum thickness value with the highest joint strength for Cu and Si combined alloy was smallest. By Cu and Si combined addition, our proposed guideline of the interfacial structure to obtain the joints strength more than 70 MPa was satisfied more easily. It was concluded that alloying of both Cu and Si to aluminum alloys improves the bondability of the joints.