Properties of as welded and heat treated pure titanium-7075 Al-Zn-Mg alloyfriction weld joints

The effects of joining conditions and an age hardening post-weld heat treat ment (PWHT) at 120 degreesC for 24 h on the tensile strength and metallurgi cal properties of dissimilar friction joints between pure titanium and age strengthened 7075 Al-Zn-Mg alloy were investigated. Highest strength was ac hieved using intermediate friction pressure (150 MPa), short friction time (0.5 s), and high upsetting (forging) pressure (400 MPa). The joint tensile strength decreased when the joint diameter was increased from 8 to 16 mm. The joint tensile strength of as welded (AW) dissimilar joints was similar to that of PWHT joints with diameters of 8, 12, and 16 mm. Detailed TEM con firmed that there was a negligible difference in the thickness of the inter metallic layer formed at the thickness of the intermetallic layer formed at the dissimilar joint interface for AW and PWHT joints. While the intermeta llic phases formed at the joint interface comprised Al3Ti, tau (Ti2Mg3Al18) , and Al in AW joints, they consisted of Al+tau or Mg2Al3+tau +Al in PWHT j oints. Softened regions were generated in 7075 base material immediately ne xt to the interface in AW joints. Post-weld heat treatment increased the ha rdness of the softened region almost to that of as received 7075-T6 base ma terial in 12 and 16 mm diameter joints. In contrast, the hardness of the so ftened region in 8 mm diameter joints could not be recovered to that of the as received material. This was a results of overaging and coarse precipita tes in the softened region produced during the friction welding operation.