Influence of Water Cooling Assisted Microplasma Arc Welding of Ti6Al4V Alloy: Correlations with Microstructure

Abstract

To improve the thermal-metallurgical-mechanical performance of the welded structure, the low-temperature water cooling is applied to assist welding Ti6Al4V alloy with filler wire. The behavior pattern of the thermal history is critically assessed with the aid of finite-element based heat transfer model. The shape of the simulated heat-affected zone is well agreed with experimentally measured values. The critical assessment on the performance of the weld joint is evaluated by metallographic analysis, energy dispersive spectrometer and micro-tensile. Increasing the flow rate and decreasing the cooling temperature can increase the cooling rate of the weld. As the rate of cooling increases, the cooling time is shortened by 15% and the concentration of oxygen in the weld area decreases from 10.84 to 6.98%. As the cooling rate increases, the effect of microstructure optimization of weld is enhanced. Blocky plate-shaped α′-martensite is apparent at a lower cooling rate, whereas the transformation of fine acicular α martensite is more complete at higher cooling rate. The dimensional variation of acicular α′ at the fusion zone has a significant influence on strength. The mechanical properties and hardness of welded joints are obviously improved with the temperature decrease.