Numerical Simulation And Experimental Study On Annealing Distortion Of Ti6Al4V Thin-walled Parts

Ti6Al4V alloy, widely applied in aviation and aerospace fields, is regularly used in annealed state. However, titanium alloy parts often have large annealing distortion due to their low elastic modulus and complex initial stress distribution. Therefore, annealing distortion of Ti6Al4 V sheets was investigated using the combination of numerical simulation and experimental methods. Meanwhile, the influence of process parameters on annealing distortion and hot sizing of titanium sheets were researched. Then, the process parameters and fixture were optimized to control the annealing distortion of thin-walled Ti6Al4 V parts.Firstly, thermal-viscoplastic and thermal-elastic-plastic annealing models were established respectively with MSC.marc to simulate Ti6Al4 V annealing process. The results indicated that creep was the key factor to accurately predict distortion. And thermal-viscoplastic model was more sophisticated than thermal-elastic-plastic model in predicting annealing distortion. Meanwhile, the internal residual stresses, which changed strain distribution and forced the sheet to bend, were the fundamental reason to cause distortion. Besides, residual stresses released in form of elastic strain exhibiting hysteresis in annealing process.Secondly, we studied the influence of process parameters on annealing distortion by numerical simulation and experimental verification after the optimization of annealing temperatures. The results showed that annealing treatment improved the strength of titanium alloy, but had no obvious effect on the elongation. The increase of annealing temperature and holding time, along with the reduction of heating rate and cooling rate, led to the rise of annealing distortion.Finally, the effect of process parameters on hot sizing and annealing distortion were investigated respectively. The results showed that the increase of annealing temperature and holding time, along with the decrease of heating rate and cooling rate, resulted in the rise of the final deformation of hot sizing. Meanwhile, gravity and fixture had significant effect on annealing distortion of titanium alloy. Fixture form, influencing the effect of gravity on parts deformation in annealing process, decided the final deformation. On the basis of the above studies, the absolute final deformation of T shaped parts was less than 0.08 mm in the fixture constraint with the optimization of annealing process parameters and fixture. The final deformation of T parts was in the range of ±0.06 mm. The fixture design was effective in controlling heat treatment distortion.