Effects of Alloying Si and Cu to Al Alloys on Interfacial Reaction and Joint Strength in Dissimilar Metals Joints of Al Alloys Steel

In the present study, dissimilar joining of 6000 type Al alloys and a low-carbon steel was carried out using diffusion bonding process. The influences of alloying elements, such as Si, and Cu, in the Al alloys were fundamentally investigated, and the quantitative relationship between the growth of the reaction layer and the joint strength was also evaluated. The IMC at the interface of the steel side was identified to be Fe2Al5in all cases. The reaction layer at the Al alloy side changed from a FeAl3layer to an Al-Fe-Si ternary compound layer with increasing Si content in Al alloy more than 1.0mass%. The Al-Fe-Si ternary compound layer uniformly formed at the initial stage of the interfacial reaction. Alloying of Cu to the Al alloy promoted the formation of the Al-Fe-Si ternary compound including Cu. It was suggested that the growth of these intermetallic layers exhibited diffusion-controlled growth behavior. The strength of the Al alloys to the steel joint showed a maximum value at a certain thickness of reaction layer in all kinds of the joints. Moreover the joint strength obviously increased with Si contents of the Al alloys. Moreover, the combined alloying of Si and Cu to Al alloys notably improved joint strength. Thus, the formation of the Al-Fe-Si ternary compounds had a beneficial effect on the strenght of the dissimilar metals joints. This is thought to be because the Al-Fe-Si ternary compounds thinly and uniformly form at the interface in the early stage of bonding. In conclusion alloying of Si and Cu to Al alloys improved bondability in dissimilar joining of the Al alloys to the steel.