Interlayer growth at interfaces of Ti/Al–1%Mn, Ti/Al–4·6%Mg and Ti/pure Al friction weld joints by post-weld heat treatment

The interlayer growth at interfaces of Ti/Al–1%Mn and Ti/Al–4·6%Mg weld joints was studied by postweld heat treatment. The heating temperatures ranged from 676 to 873 K (400–600°C) and maximum heating time was 360 ks (100 h). The basic mechanism of interlayer growth for pure Ti/pure Al friction weld joint was also estimated. The interlayer growth rate of Ti/Al–4·6%Mg joint was much faster than for the Ti/ Al–1%Mn joint. The interlayer mainly consisted of (Al,Si)₃Ti for the Ti/Al–1%Mn joint, and Al₁₈Mg₃Ti₂ for the Ti/Al–4·6%Mg joint. While the interlayer grew from Al alloy substrate to the Ti side for the Ti/Al–1%Mn joint, it grew from the Ti substrate to the Al alloy side for the Ti/Al–4·6%Mg joint. The interlayer growth stopped for several hours on heating for 36 ks (10 h). Neither linear nor parabolic time-dependence relations could be exactly fit to the interlayer growth rate for both joints. The interlayer growth of Ti/Al–1%Mn was proportional to heating time raised to approximately 0·85. The crystal direction of Al₃Ti interlayer growth of the Ti/Al joint was close to 〈001〉 and 〈111〉 directions obtained by OIM method. Nucleation and nuclei growth were observed at the interface of the Ti/Al joint. The nucleation and the nuclei growth are the reason for the phenomena (time dependence) described above.