Bonding mechanism in roll bonding of low carbon steel and aluminium alloys

Abstract

Roll bonding of low carbon steel and pure aluminium sheets is already an established process in industry, In this study, alloying additions were made to aluminium for understanding their effect on the joint strength and bonding mechanism. Heavy mechanical working leads to work hardening, which necessitates post heat treatment. However, such treatment causes formation of brittle intermetallic compounds (IMC) at the interface and considerably reduces the bond strength. Therefore, the effect of alloying elements on growth of IMC layer and on bond strength of the joints after post heat treatment was studied. Effect of carbon content in steel on the growth of IMC layer was also investigated. It was found that except for the SPCC/A1-1.5% Si joint, the peel strength values of the joints made with different aluminium alloys were lower than that of SPCC/A1050 joint. The bond strength depends on area of aluminium remained on the steel surface after peeling. The joints with A1-5% Mg showed very low peel strength indicating poor adherence due to hardening. However, on its post heat treatment at 623 K there was increase in its peel strength. As holding temperature increased, there was considerable growth in the IMC layer thickness which reduced the peel strength. On the other hand, joints with Al-Si alloys suppressed the IMC layer growth and therefore failed in aluminium base metal during peel test. Depending on the alloying elements in aluminium alloy, there is large difference in the growth of IMC at the interface. In case of Mg and Cu addition, the growth was fast whereas in case of Si addition it was slow. Variation in carbon content in steel did not affect the growth of IMC layer, but change in % reduction in steel had some effect on the IMC growth rate.