Abstract: In order to solve the problems of 3D bending and forming of difficult-to-machine material profiles such as titanium alloy, a multi-point 3D hot stretch-bending process was proposed and the forming equipment was developed. The effects of the processing parameters such as pre-stretching amount, post-stretching amount and forming temperature on the 3D hot stretch-bending of L-shaped cross-section profiles for TC4 titanium alloy were explored through the forming tests. Among them, the forming temperature is the most important factor affecting the springback deformation. The best forming conditions are achieved when the pre-stretching amount is as 100%εs and the post-stretching amount is as 20%εs (εs is the yield strain parameter) at a certain temperature. Based on the results of forming tests and material mechanics property tests, a finite element simulation model was established to predict the forming processes and springback processes of multi-point 3D hot stretch-bending process, and the errors of springback prediction are less than 15%, which verifies the validity of the model. In addition, the microstructures of TC4 titanium alloy before and after forming processes were observed. The results show that compared with the initial undeformed sample, the phase transformation of TC4 titanium alloy after 3D hot stretch-bending is produced, the (101-0) grain surface texture intensity is significantly increased, the two-phase grain sizes are reduced, the plastic deformation ability of TC4 titanium alloy formed parts is improved, and the geometrically necessary dislocation density is increased.

Key words: TC4 titanium alloy, 3D hot stretch-bending, springback prediction, microstructure

摘要： 为解决钛合金等难加工材料型材的三维弯曲成形问题，提出了多点三维热拉弯成形工艺并研制了成形装备。通过成形试验探索了预拉伸量、补拉伸量和成形温度等工艺参数对TC4钛合金L形截面型材的三维热拉弯成形规律，其中成形温度是影响回弹变形的最主要因素，当温度一定时，采用预拉伸量为100%εs、补拉伸量为20%εs时（εs为屈服应变参数），型材达到最佳的成形状态。基于成形试验和材料力学性能测试结果建立了预测多点三维热拉弯成形工艺成形过程和回弹过程的有限元仿真模型，回弹预测误差小于15%，验证了模型的有效性。此外，对成形前后的TC4钛合金进行了微观组织观测，研究结果表明，与初始未变形样件相比，三维热拉弯成形后的TC4钛合金产生了相变，（101-0）晶面织构强度显著提高，两相晶粒尺寸均有所减小，TC4钛合金成形件的塑性变形能力得到了提高，且几何必需位错密度有所增大。

关键词: TC4钛合金, 三维热拉弯成形, 回弹预测, 微观组织