TC4钛合金承重框双道双侧不等熔深EBW接头研究

Study on double-side and double-pass unequal penetration EBW TC4 joint used for hollowed-out load-bearing thick beam

摘要:

针对140mm厚TC4钛合金镂空承重框的结构特征提出双道双侧不等熔深的电子束焊接（EBW）方案，进行焊接试验并对接头组织性能进行了分析。发现焊缝区组织性能在厚度方向有较明显的不均匀现象，两道焊缝根部重叠区是最值得关注的部位。两道焊缝根部重叠区存在大量针状α′相和点状离散分布的β相，针状相短小、相互交错现象明显；接头中其它焊缝区域观察到针状α′相和分布在原始β晶界的α相，但板条较长且排列具有较明显方向性。两道焊缝根部重叠区显微硬度比接头其它焊缝区域显微硬度（341HV~346HV）高出约10%。两道焊缝根部重叠区的焊缝室温冲击功比接头中其它焊缝区域室温冲击功（约47J）低约11%。两道焊缝根部发生重叠的区域焊接接头抗拉强度最低。结合有限元仿真发现大厚度TC4双道双侧不等熔深EBW接头焊缝根部重叠区在900℃附近冷却速度高于焊缝其它区域，是导致重叠区域与焊缝其它区域之间组织性能差异的重要原因。接头拉伸都断裂在母材区。研究表明采用双道双侧不等熔深EBW焊接方案制造大厚度镂空钛合金承重框是可行的，建议实践中可采取提高母材厚度方向组织性能均匀性、严格控制两道焊接之间时间间隔等措施。

Abstract:

In this paper, according to the structural characteristics of 140mm thick hollowed-out load-bearing TC4 titanium alloy beam, a double-side and double-pass electron beam welding (EBW) scheme with unequal penetration was proposed. The welding test was carried out and the microstructure and properties of the obtained joint were analyzed. It is found that the microstructure of the weld zone is obviously non-uniform in the direction of thickness, and the overlapping zone at the root of the two welds is the most noteworthy part. There were a lot of needle α′ phase and scattered β phase in the overlapping area of the root of the two welds, while the needle phase was short and the interlacing phenomenon of α′ phase was obvious. The needle α′ phase andα phase distributed in the original β grain boundary were observed in other weld areas of the joint, but the laths were longer and arranged in a more obvious direction. The microhardness of the weld in the overlap zone of the root of the two welds was about 10% higher than that of the other weld zones in the joint (341HV~346HV). At room temperature, the impact energy of the weld in the overlap zone at the root of the two welds was about 11% lower than that of the other weld zones in the joint (about 47J). The area where the roots of the two welds overlap was the area where the joint had the lowest tensile strength. With the aid of finite element simulation, it was found that the cooling rate around 900℃ of the overlapping area of the root of the two welds was higher than that of the other areas of the welds, which was an important reason for the difference in the microstructure and performance between the overlapping area and the other areas of the welds. It was noted that all joints were broken in the base material area during tensile tests, and it was believed that the inhomogeneity of microstructure and properties of large-thickness forgings in the direction of thickness resulted in the inhomogeneity of tensile strength of joints. The results show that it is feasible to use double-side and double-pass unequal penetration EBW welding scheme to fabricate thick hollowed-out load-bearing TC4 titanium alloy beam. Meanwhile, some beneficial measures such as improving the uniformity of microstructure and property of the base material and strictly controlling the interval time between two passes of welding are recommended