INFLUENCE OF SILICON IN ALUMINUM ON THE MECHANICAL-PROPERTIES OF TITANIUM ALUMINIUM FRICTION JOINTS/

The influence of post-weld heat-treatment and of residual silicon in a luminium on the mechanical properties of dissimilar friction joints be tween titanium and aluminium was investigated. Although joint tensile strength and bend test properties were drastically reduced following p ost-weld heat treatment, the responses of Ti/h.p. Al and Ti/c.p. Al jo ints were quite different. The tensile strength and bend test properti es of Ti/h.p. Al joints were markedly decreased by heat-treatments inv olving shorter holding times at lower temperatures. Joint failure in p ost-weld heat-treated joints was associated with Al3Ti formation at th e bondline region. The growth rate of the Al3Ti intermetallic layer at the joint interface was much faster in post weld heat-treated Ti/h.p. joints. More than 20 at %Si segregated in the region between the tita nium substrate and the Al3Ti intermetallic phase in heat-treated Ti/c. p. Al joints. It is suggested that silicon segregation retards Al3Ti f ormation by acting as a barrier to titanium and aluminium diffusion at the joint interface.