毕业论文(模板).doc

XXXX学院毕业论文（设计） 论 文 题 目 钛合金激光焊组织及性能研究 专 业 焊接技术与工程 姓 名 学 号 指 导 教 师 二零一四年五月 钛合金激光焊组织及性能研究 摘 要 本文综述了钛合金激光焊的基本原理、特点和国内外研究现状，并针对4mm的Ti-70钛合金试板进行了钛合金激光焊接工艺试验，研究了工艺参数（激光离焦量、激光功率、保护气流量、托罩位置以及焊接速度等）对焊缝成形的影响，焊后对焊缝的宏观形貌及微观组织进行了观察和分析，以及焊缝硬度的测试，并对所得接头进行拉伸和弯曲的力学性能分析。试验结果表明：在激光焊接过程中激光功率相同，但由于离焦量存在差异会导致堆焊时的熔透产生很大的差别；通过调整焊接参数，以及背面保护、托罩保护等保护措施，最终获得了比较满意的钛合金焊接接头；采用激光焊接，焊缝的热影响区相对传统电弧焊接宽度要窄的多，但在焊缝和母材交界附近存在较明显的过渡不圆滑的现象，容易在此处应力集中；经拉伸后焊接接头的断裂位置都在母材，分析其应力应变曲线可知，两试样的平均拉伸强度σb为676 MPa，屈服强度σ0.2为608 Mpa；背弯90o 后试样完好未发生裂纹和断裂现象，而在正弯试验时发现，当弯曲角度较大时发生断裂现象。 关键词：钛合金；激光焊接；力学性能；微观组织 Titanium and properties of laser welding Abstract This paper reviews the basic principles of laser welding titanium alloys, characteristics and research situation, and 4mm for the Ti-70 titanium alloy test panels for the laser welding process, a study of the process parameters on the effects of weld, weld after weld macro-morphology and microstructure were observed and analyzed, and the weld hardness testing, and from joint to mechanical properties of tensile and bending analysis. The results showed that: in the laser welding process, the same laser power, but because of differences in the amount of defocus lead to penetration when welding a big difference; by adjusting the welding parameters, and the back of the protection, care cover protection and other protective measures, ultimately a more satisfied with the titanium alloy welded joints; the use of laser welding, the weld heat affected zone width compared to conventional arc welding and more to narrow, but near the junction of the weld and base metal there is no smooth transition to the more obvious phenomena, stress concentration here is easy; by stretching the location of the fracture of welded joints in the base material, to analyze the stress-strain curve shows that the average tensile strength of two specimens σb to 676