Abstract
In this study, the long-discussed question of the effect of interfacial compound layer in inertia friction welded 2 series aluminum (Al) alloy/steel joint is investigated by altering the state of the base metal, including heat treatment of Al alloy and surface modification of steel. It was found out that the precipitate formed in the precipitation process of Al alloy during cooling strongly affected the formation of interfacial intermetallic compounds (IMCs), rather than its original pre-existing precipitates. At low heat input, the incomplete extrusion of oxide layer led to the existence of nanoscale Fe-Al-O amorphous layer together with the nanoscale Al2Cu occasionally precipitated (semi-coherent with Al) at the interface. At high heat input, the enhanced coupling effect of heat and plastic flow of Al alloy resulted in the possible reaction between Fe, Si and Al2Cu to form a Fe4Al13 type IMC, Al67.5Fe20.7Cu6.2Si5.6, with a lower formation enthalpy, but the non-uniform reaction caused the remnant Al2Cu in the submicron-scale IMCs layer, being non-uniformly distributed. Local tensile tests indicated that joint strength was negatively correlated with the thickness of the IMCs layer in which the joint with nanoscale Fe-Al-O amorphous layer showed the highest bonding strength.
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