Abstract
Investigations were conducted on TB8 titanium alloy to assess the influence of aging heat treatment on microstructure and phase transformations induced by laser oscillating welding, and establish a correlation between tensile properties and microstructure. Low-temperature aging joint consists of ω phase and β phase, while high-temperature aging joint is comprised of α phase and β phase. The formation of poor and rich precipitation zone in weld area was due to segregation of major alloying elements like Al, Mo and Nb. Low-temperature aging deteriorates plasticity of joints, but high-temperature aging improved ambient-/elevated-temperature tensile properties. The effect of aging temperature and aging time were discussed in depth. After aging treatment at 450° Celsius for 1 h, intermediate ω phase in gathering place transformed to α phase, but dispersed ω phase still retained. With the increase of aging temperature and aging time, size of α precipitate increased. Note that there is a significant increase (85%) in tensile strength after high-temperature aging treatment and Portevin-Le Chatelier (PLC) effect can be avoided under thermo-mechanical loading conditions. It was found that after 1 h of aging treatment at 550° Celsius followed by air cooling, the welded joints owned the best tensile properties at both ambient and elevated temperature.
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