Roll bonding behaviour of Ti-6Al-4V sheets during pack rolling

Abstract

Low density, excellent corrosion resistance, moderate strengths at high temperatures make titanium based alloys candidate materials for advanced aerospace structures. Advanced joining techniques are emulating for fabrication of complex aerospace structures. Roll bonding is one such solid state joining technique where bonding between two rough and clean surfaces is obtained under high temperature and pressure. The work horse dual phase titanium alloy Ti-6Al-4V finds extensive structural application in aerospace and space industries. In the present study, two Ti-6Al-4V sheets are stacked together and encapsulated in a mild steel can followed by evacuation and hot crimping. The pack is extensively deformed to ~84% reduction in thickness employing conventional hot rolling mill. Partially roll bonded 0.74mm thick sheets were obtained and microstructural evolution was studied using light microscopy and scanning electron microscopy. The incompletely bonded interface was analyzed through elemental mappings by Electron Probe Micro Analyzer and compared with completely bonded region. The partially bonded region revealed the presence of aluminium oxide at the interface which possibly could have hindered complete bonding at that region. The room temperature tensile properties of as-roll bonded Ti-6Al-4V nearly approaches the base material properties.