Microstructure and Properties Study of TA18 Titanium Alloy Tube Differential Temperature Necking and Thickening Forming Based on Temperature Gradient Positioning

A finite element model was established to simulate the necking and thickening process of TA18 titanium alloy thin-wall tubes to compare the effect of differential temperature and isothermal methods on the temperature and wall thickness distributions of the tubes. It is found that the temperature gradient of differential temperature tubes shifts from the force transfer area to the necking area, and these tubes exhibit a thicker thickening area and a thinner necking area compared to their isothermal counterparts. The experiments on the necking and thickening of TA18 titanium alloy tubes were conducted using both differential temperature and isothermal methods. The results show that the differential temperature method is a superior forming method compared to the isothermal process. The major thickening occurs in the thickening area of the differential temperature tube, while it occurs in the necking area of the isothermal tube. The average wall thickness of the differential temperature tubes is 25% greater in the thickening area, while it is 23% thinner in the necking area, compared to the isothermal tubes. We conducted EBSD tests on TA18 titanium alloy thin-walled tubes; the results showed that dynamic recrystallization occurred in the necking and thickening regions, with significant grain refinement. The grain size in the necking region was smaller than that in the thickening region.