Effects of heat-treatment temperature on the adhesive bonding performance of Ti–6Al–4V alloy

In recent years, titanium alloys have been increasingly applied in the aerospace industry due to their low density, excellent mechanical properties, and corrosion resistance. Compared with bolting and welding, adhesive bonding offers advantages including reduced weight and more uniform stress distribution. In this work, a simple surface-activation method, namely electric-furnace heating at 200–800 °C for 1 h was evaluated to improve the adhesive bonding of ground Ti-6Al-4V sheets. Heat treatment produced a TiO 2 -rich surface, reduced adventitious carbon, and increased wettability. The optimum condition was 400 °C for 1 h, which yielded the highest energy release rate ( Gc ) of 1455 J/m 2 in double cantilever beam (DCB) tests, with a predominantly cohesive failure mode (96%). This was markedly higher than that of the as-ground surface, which exhibited a Gc of 924 J/m 2 and a cohesive failure proportion of only 46%. At 800 °C, a thick Al 2 O 3 -containing layer formed and early delamination occurred at the brittle oxide/Ti-6Al-4V interface, driving Gc toward zero. After the treatment, the surface became recontaminated when the sheets were exposed to laboratory air above 48 hours, resulting in hydrophobic recovery and a reduction in Gc . The comprehensive results indicate that an effective condition for Ti-6Al-4V is 400–600 °C for ∼1 h in air, followed by immediate bonding before any recontamination. • Furnace heating of Ti-6Al-4V at 400°C for 1 h maximized adhesive bond fracture energy. • At 800 °C, a thick Al 2 O 3 layer formed and failed by cohesive fracture in the oxide. • Air exposure >48 h caused recontaminated, reducing wettability and bond strength.