【作者】 李慧；

【导师】 刘喜明；

【作者基本信息】 长春工业大学 ， 材料学， 2014， 硕士

【摘要】 钛合金因具有无磁性、无毒性、强度高、耐腐蚀、加工性(成形与焊接)好等许多优良特性,被誉为海洋金属、空间金属和未来金属,广泛应用于海洋钻探、压力容器、深潜器、核潜艇、宇航、舰船、能源冶金、交通运输、石油工业等领域。各种各样的问题都会在钛合金的使用过程中产生,尤其是焊接时造成的缺陷。因此,关于钛合金的焊接技术及其焊接接头组织性能的研究迫在眉睫。本文实现了厚板钛合金的窄间隙自动化焊接,同时借助金相显微镜(OM)、X射线衍射仪(XRD)、显微硬度计(HV)、扫描电子显微镜(SEM)、力学性能测试等手段,对钛合金窄间隙TIG焊的焊缝成形、接头各区域的组织特征、力学性能以及断口形貌进行了研究。获得的主要结论有：(1)通过一系列的工艺调试,确定了16mm厚钛合金板材可以实现侧壁熔合良好、焊缝成形美观的焊焊接头的最佳匹配参数。焊接电流控制在200A-270A之间；焊接电压：11.0～11.5V；送丝速度：50～100m/h；焊接速度：6m/h。(2)母材区的显微组织为片状和细条状的初生α相以及少量均匀分布在基体上的残余β相；α’相六方马氏体是焊缝区的显微组织；热影响区分为细晶区和粗晶区两部分,细晶区的显微组织是初生α相、等轴α相、β相,粗晶区晶粒的长大程度比较显著,其显微组织为少量的初生α相和α’相。通过对母材区和焊缝区进行的成分分析,焊缝区的元素种类与母材区的元素种类相比,元素种类保持不变。对比焊缝区的合金元素浓度与母材区的合金元素浓度,发现焊缝区的合金元素浓度变化较小。这说明钛合金中的合金元素受到的烧损程度微乎其微,而且元素呈现为比较致密均匀的分布形态。(3)在低焊接线能量(A组：1320KJ·m-1～1452KJ·m-1)、中等焊接线能量(B组：1518KJ·m-1～1656KJ·m-1).高焊接线能量(C组：1725KJ·m-1～1863KJ·m-11)的条件下,焊接接头从顶部到底部的平均抗拉强度为792MPa、749MPa、803MPa,都分别超过了母材的96%以上。Ti75合金母材的冲击韧性为1067KJ/m2,焊缝的冲击韧性为970KJ/m2.868KJ/m2.897KJ/m2,分别达到了母材的81%以上。母材的冲击韧性普遍高于焊缝的冲击韧性。在1518KJ·m-1的焊接线能量条件下,弯曲角可达1350,弯曲性能良好。(4)Ti75合金母材的硬度为280HV左右,焊接接头由母材到焊缝中心的横向硬度表现为先升高后降低的趋势,热影响区的硬度达到峰值。(5)大量的等轴韧窝是拉伸试样断口的最主要的微观形貌。抛物线形韧窝是冲击试样断口的典型微观特征。均属于韧性断裂机制。更多还原

【Abstract】 Titanium alloy has a lot of exceptional characteristics including non-magnetic, non-toxic, reasonable high strength to weight ratio, excellent corrosion resistance, high temperature creep resistance and good formability. And it is regarded as the "marine metal","space metal" and "future metal". It is widely used in ocean drilling of deep sea diving, pressure vessel, nuclear submarines, aerospace, ships, weapons and equipment, energy, metallurgy, transportation, oil industry and other fields.All sorts of problems can be produced in the process of using titanium alloy especially welding defects. Therefore, the research on welding technology of titanium alloy and its welded joint organization and performance is imminent. Narrow-gap TIG welding equipment could be successfully applied to the automatic welding of thick-plate titanium alloy. The weld seam form, microstructure, properties and fracture morphology of Ti75titanium alloy narrow-gap TIG welded joint are studied by means of optical microscope(OM), X-ray diffraction(XRD), micro-hardness tester(HV), scanning electron micro-scope(SEM) and other mechanical testers. Main conclusions obtained are as the following:(1) The best matching parameters of realizing high quality joining of16mm thick titanium alloy plate are obtained through a series of process debugging. The welding current is200A-270A. Welding voltage is11.0V～11.5V. Wire feeding speed is50m/h～100m/h. Welding speed is6m/h.(2) The results show that the microstructure of base metal consists of long strip and block primary a phase, and a small amount of residual β phase sprinkled. The microstructure of weld zone was composed of hexagonal close-packed (HCP) a’ phase. The microstructure of heat affected zone (HAZ) may be divided into two regions:fine grain region and coarse grain region. The microstructure of fine grain region was consisted of primary a phase and transferred β containing equiaxial a, while the microstructure of coarse grain region was constituted of little primary a phase and needle martensite a’. It is found that the weld seam area elements are changed small by energy spectrum analysis in the base metal and weld seam, showing that the alloy elements loss is less in titanium alloy with uniformly distributed. Through to the composition analysis of base metal and weld area, compared the element types of weld area element types with that of the base metal area, element types remain unchanged. It is found that the element net weight and strength of the weld area changes small by comparing elements net weight and strength of the weld area to that of the base metal area. This shows that the weight of the alloy elements in titanium alloy by a negligible damage degree and elements are presented to compare the dense homogeneous distribution form.(3) Under the condition of different heat input, Ti75alloy joint has a similar tensile strength in the top, but the change of the joint strength is tended to come down first and then go up. from top to bottom. And with the increase of welding heat input, the tensile strength of joint is also gradually increased. The average tensile strength of welded joint is respectively792MPa,749MPa and803MPa, may reach over about96%of the base metal. Ti75alloy impact toughness is1067KJ/m2, the impact toughness of weld seam is respectively970KJ/m2,868KJ/m2,897KJ/m2, may reach over about81%of the base metal. The impact toughness of weld seam is generally lower than that of the base metal. And as welding heat input is increasing, the change of weld seam impact toughness is tended to come down first and then go up. In the1518KJ-m-1welding heat input conditions, bending Angle is135°, and the bending performance is good.(4) The micro-hardness of Ti75alloy is around280HV, the welding joint transverse micro-hardness from the base metal to the weld center is tended to go up first and then come down, and that of heat affected zone arrives at a peak value.(5) Tensile fracture microcosmic fracture presents large amounts of axial toughening dimple. Impact fracture microcosmic fracture presents parabolic toughening dimple. Fracture mechanism belongs to ductile fracture.更多还原