摘要
The superplastic forming of Ti alloy welds has great application prospects in producing integrated components. However, the nugget zone（NZ） of the Ti alloy welds,produced by fusion welding or conventional friction stir welding（FSW）, consists of lamellar micro structure, which exhibits either low superplasticity or high superplastic temperautre and low strain rate. As a result, the NZ plays a leading role in hindering the superplastic forming of the whole welds.In this study, submerged friction stir welding（SFSW） was conducted in Ti-6Al-4 V alloy for the first time, and a defectfree weld with the NZ consisting of a strip microstructure was obtained. The NZ exhibited a low-temperature superplasticity at 600℃, which was the lowest superplastic temperature ever reported in the Ti alloy welds. Besides, at 800℃, the NZ showed high strain rate（3×10^（-2） s^（-1）） superplasticity and a largest elongation of 615% at 1×10^（-3） s^（-1）. Compared to conventional FSW joints, the NZ of SFSW joint exhibited a much lower flow stress and a decrease in optimal superplastic temperature by 100℃. This is mainly attributed to the easy globularization of the strip microstructure, enhancing the ability of grain/phase boundary sliding.
钛合金焊接接头超塑成型用于生产整体构件具有广泛应用前景.熔焊或常规搅拌摩擦焊(FSW)通常得到具有片层组织的焊核,从而导致过低超塑性、或过高超塑温度以及过低应变速率,成为影响接头整体成型的关键.本研究首次采用水下FSW(SFSW)对Ti-6Al-4V进行焊接,得到焊核为条带组织的无缺陷接头.焊核在600℃下仍具有超塑性,是目前实现钛合金焊接头超塑性的最低温度.此外,焊核可在800℃下和高应变速率(3×10^(-2)s^(-1))下实现超塑性,并在1×10^(-3)s^(-1)下获高达615%的延伸率.与常规FSW相比,SFSW焊核的最佳超塑温度下降了100℃且流变应力大幅下降,其优异超塑性能主要是由于条带组织在超塑变形中极易球化,提高了晶界/相界滑移能力的结果.
基金
supported by the National Natural Science Foundation of China under Grant(51471171,51601194,and 51331008)
