The influence of aluminium intermediate layer in dissimilar friction welds

Friction welding of 304 austenitic stainless steel to commercially pure titanium was carried out using commercially pure aluminium as an interlayer of different thicknesses viz., 0.5, 1.1, 1.7 and 2.3 mm. The interlayer was aimed at preventing the occurrence of direct contact between the parent metals, which otherwise would lead to the formation of Ti-Fe intermetallic phases. These intermetallic phases can seriously affect the weld properties. The microstructure of the friction welded joint interfaces was characterized by means of optical microscopy, scanning electron microscopy, energy dispersive spectroscopy and X-ray diffraction analysis. The maximum hardness at the Ti – Al interface was attributed to the presence of AlTi and Al3Ti intermetallics. Tensile tests were conducted to evaluate the strength of the joints and the results showed the maximum strength (272 ± 9 MPa) was achieved in the joint having 1.7 mm thick interlayer. The analysis of fractured surfaces revealed that the failure was confined to the aluminium layer at the Ti – Al interface and was transgranular with flat facets.