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.