Microstructural characterisation and corrosion behaviour of aluminium alloy/steel hybrid structure produced by friction welding

An aluminium (Al) alloy to stainless steel friction welded joint, being of potential as an alternative for the existing structural component, was obtained under specifically designed heat inputs at three different levels (low, medium and high). Heat input significantly affected the mechanical properties of the joint where the joint welded at the medium level posed the highest tensile strength (325 +/- 14 MPa). When the heat input was at a low level, an un-welded zone was observed with no obvious signs of IMCs. Upon increasing heat input to a higher level, weld defects disappeared with sub-micron sized IMCs layer formed. The IMCs layer demonstrated rather distinct thickness characteristics at different interfacial regions, but a higher heat input resulted in a thicker layer at similar regions. Although it was identified that a thicker IMCs layer might pose an adverse effect on the corrosion resistance, the friction welded Al alloy/steel joints had only a marginal change in corrosion potential and corrosion current intensity under various heat inputs, presumably due to fine (sub-micron) sized IMCs formed at various regions along weld interface. Therefore, friction welding could realise the sound joining of Al alloy and steel with both satisfying mechanical properties and corrosion resistance by restricting the IMCs at sub-micron level.