Microstructural characterisation of rotary friction welded AA6082 and Ti-6Al-4V dissimilar joints

Abstract The aim of this work was to investigate the weld interface and microstructure of a rotary friction welded (RFW) Ti-6Al-4V to AA6082 joint for the purpose of future spacecraft applications. A recent initiative by the European Space Agency (contract No. 4000111471/14/NL/PA) towards a more sustainable materials and processes selection has given the development of advanced joining techniques significant momentum. As part of this strategic development, it was proposed to produce propellant and pressurant tanks with aluminum alloys, joined to the Ti-6Al-4V tubing and pipework surrounding the tank with advanced joining methods. Consequently, Omnidea-RTG and IWS were tasked to develop the joining of dissimilar, tube and rod shaped materials via rotary friction welding, a solid-state welding technique. Thorough parameter optimisation of the welding process has resulted in consistent and reliable welds with excellent mechanical properties. Nonetheless, due to the complex kinetics of the RFW process, the potential formation of brittle intermetallic compounds at the weld interface is still a possibility. Therefore, the microstructure of rotary friction welded AA6082 and Ti-6Al-4V joints was investigated. Emphasis was placed on the detailed inspection of the weld interface and the surrounding base alloys, as well as the compositional evolution throughout the interface region.