热处理对钛合金激光焊接接头超塑性变形均匀性的影响

发布时间：2018-04-23 00:17

  本文选题：钛合金激光焊/超塑成形 + 淬火处理　； 参考：《南昌航空大学》2017年硕士论文

【摘要】：焊接/超塑性成形组合技术在钛合金多层空心轻量化结构方面有着极大的优势。目前在焊接/超塑性成形运用较为成熟的焊接方法为扩散连接/超塑性成形(SPF/DB),但扩散连接/超塑性成形(SPF/DB)还存在一定的缺陷,如零件生产效率低、零件结构设计和制造的灵活性差等问题。激光焊可以有效克服钛合金扩散连接困难,形成性能良好的接头,但激光焊/超塑成形技术在变形后出现颈缩和组织不均匀现象,这将严重影响零件的性能。所以改善激光焊超塑性变形接头变形均匀性和组织均匀性是激光焊/超塑成形技术突破的关键,本文以TC4钛合金激光焊接接头为研究对象,研究淬火处理对TC4钛合金激光焊超塑变形的组织均匀性和拉伸均匀性进行了研究,得出以下结论:在1000℃温度下淬火时,接头各区域为β相,母材与焊缝β相尺寸之比为1.2,显微硬度差值为10HV,淬火处理可以改善TC4钛合金激光焊接接头组织状态,提高焊接接头均匀性,随着淬火温度的升高,接头整体组织均匀性增强:当淬火处理960℃~1000℃,焊接接头在超塑性变形过程中,接头峰值流变应力15MPa~60MPa之间,延伸率在178.362%~581.733%之间。在相同变形条件下,随着淬火温度的升高,接头应力应变曲线上移;焊接接头峰值流变应力随着淬火温度的升高而增大,随着变形温度的升高而降低,随着应变速率的升高而增加;焊接接头的延伸率随含淬火温度的增大而减小,随变形温度的升高而增大,随应变速率的增大而减小。通过金相显微组织观察发现,淬火处理可以提高焊接接头各区域变形协调性,缓解焊接接头超塑性变形后接头出现颈缩与组织不均匀的问题。焊接接头超塑性变形初期,焊缝与母材组织由细小的针状组织转变为片层组织,超塑性变形机制以软化作用和动态再结晶为主;接头超塑性变形后期,片层组织持续长大,相互挤压断裂形成不规则组织与等轴状组织,变形协调机制以动态再结晶与球化作用为主。焊接接头超塑性变形后,接头整体组织为不规则组织与等轴状组织,焊接接头组织均匀化程度增强。本文引入组织均匀性系数M和变形均匀性系数K来表征焊接接头均匀化程度,随着淬火温度的升高,组织均匀性系数M与变形均匀性系数K增大,接头均匀化程度升高;在相同的淬火温度下,变形温度的升高或应变速率的降低均会使接头均匀化程度升高,在淬火温度1000℃,变形温度940℃,应变速率10-4s-1的条件下,接头拉伸均匀性系数值为0.9269和组织均匀性系数值为0.66134。
[Abstract]:Welding / superplastic forming technology has great advantages in titanium alloy multilayer hollow lightweight structure. At present, the more mature welding method used in welding / superplastic forming is diffusion bonding / superplastic forming (SPF / DBN), but there are still some defects in diffusion bonding / superplastic forming (SPF / DBB), such as low production efficiency of parts. The flexibility of structural design and manufacture of parts is poor. Laser welding can effectively overcome the difficulty of diffusion bonding of titanium alloy and form the joints with good properties. However, the necking and uneven microstructure of laser welding / superplastic forming technology after deformation will seriously affect the performance of the parts. Therefore, improving the deformation uniformity and microstructure uniformity of laser welded superplastic deformation joint is the key to breakthrough of laser welding / superplastic forming technology. In this paper, the TC4 titanium alloy laser welded joint is taken as the research object. The microstructure homogeneity and tensile uniformity of superplastic deformation of TC4 titanium alloy laser welding were studied by quenching treatment. The following conclusions were obtained: when quenched at 1000 鈩，

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