【作者】 王莹；

【导师】 张敏； 李继红； 叶建林；

【作者基本信息】 西安理工大学 ， 材料工程（专业学位）， 2018， 硕士

【摘要】 TA2/Q345复合板因其兼有钛的耐腐蚀性和钢的高强度,在航天航空、石油化工、海洋工程等领域具有广阔的应用前景。但是,TA2/Q345复合板焊接时,由于焊接温度场的不均匀性和材料热物理性能的差异较大,易在焊缝及其附近产生较大的焊接残余应力,促进了裂纹的萌生和扩展,从而降低结构的使用性能和服役寿命。本文以TA2/Q345复合材料盖板搭接式复杂结构焊接为主线,系统研究了复合板焊接过程中温度场、应力场演化规律和其应力调控机制,研究结果可为异质材料复合板焊接工艺的制定和焊接质量的提高提供理论依据。首先基于热-弹塑性有限元理论,采用改变填充单元材料特性的数值模拟方法再现了TA2/Q345复合材料盖板搭接式复杂结构焊接过程中的温度场和应力场的演变过程。在复合板焊接过程中,当焊接达到准稳态时基板熔池呈“卵状”,而垫板和盖板熔池均为“勺状”。复合板各道焊接时不仅对焊缝处峰值温度影响较大,而且对焊缝附近的复合板界面处热作用影响也较为显著。将温度场的计算结果作为初始载荷加载到应力场计算中发现,焊缝中部应力变化幅值较小,纵向应力均呈拉伸状态,横向应力为交替出现的拉-压状态,而焊缝两端因其温度场变化剧烈致使应力变化极为复杂,变化幅值也增减不一。同时发现,基板和盖板焊后焊缝处应力均超过了两种材料的屈服强度,垫板焊后复合板界面处峰值应力大于其焊缝处的峰值应力。其次,为了保证复合板构件在服役过程中安全运行,充分考虑到焊接残余应力对承载能力、界面结合强度及耐蚀性的影响,分别研究了基板、垫板、盖板焊接时焊接工艺对复合板残余应力的影响。结果表明,提高预热温度和缩短层间冷却时间可有效地降低基板焊接残余应力;通过减小电弧功率和道间冷却时间,增加焊接速度,并采用同向同时的焊接顺序既可减小复合板界面处和盖板焊缝表面处的残余应力,又可显著提高生产效率。由于单一因素对于复合板该接头形式约束条件下应力调控的局限性,借助优化试验设计方法对各个部分的焊接工艺进行多因素优化调控研究,发现预热150℃,冷却100s可有效提高基板的承载能力;垫板焊接时,采用冷却时间t=100s,焊接功率P=450W,焊接速度v=3.2mm/s并同向同时焊接S所得到的焊接残余应力最小,峰值等效应力最大可降低21.3%,垫板焊接工艺对界面残余应力的影响程度为S>t>P>v;盖板焊接时,最优组合为同向同时焊接S,t=(200/1000)s,v=1.2mm/s,P=1000W,峰值等效应力最大可降低31%,可使焊缝表面处应力对耐蚀性的影响最小,工艺影响主次为S>t>v>P。采用模拟获得的优化工艺对TA2/Q345复合材料盖板搭接式复杂结构进行焊接试验,通过热电偶测试热循环曲线、体视显微镜对熔池形貌表征,并用盲孔法测试残余应力,发现测量结果与模拟计算结果相吻合,拉伸性能和剪切性能均可满足实际许用要求。更多还原

【Abstract】 Due to excellent corrosion resistance and high strength,the TA2/Q345 clad plate ha s wide potentials in the aerospace,petrochemical industry,marine engineering and other fields.However,large residual stress is easily generated around the welding seam during welding TA2/Q345 clad plate because of the large differences in the temperature field and their thermophysical properties.The residual stress promotes the initiation and propagation of cracks,thereby deteriorating the performance of the structure and reducing the service life.In this investigation,the evolution of temperature field and stress field along with the stress regulation during the welding process of TA2/Q345 clad plates were studied utilizing coverplate-lap with complex structure.The research can provide the therotical basis for the welding design and the improvement on the welding quality for heterogeneous materials.Based on the thermo-elastic-plastic finite element theory,the evolution of temperature field and stress field during welding TA2/Q345 clad plate utilizing coverplate-lap with complex structure was reconstructured by the numerical simulation method along with change of the material properties for the filling unit.During welding clad plate,the baseplate molten pool is in the form of oval shape,whereas the subplate and coverplate present spoon-like shapes if the welding reaches a quasi-steady state.The welding of clad plate not only obviously influences peak temperature,but also affects heat dissipation at and around the interface of the TA2/Q345 clad plate.The stress field was simulated by the calculated result of the temperature field as the initial load,and it is found that there is a small change for the stress in the middle of the welding seam.The longitudinal stress is in the tensile state,while the transverse stress alternately changes in the tension-compression state.However,due to the change of the temperature field,the stress has an extremely complicated change at the ends of the welding seam,and the amplitude is significantly changed as well.Meanwhile,for the baseplate and coverplate after welding,the stress at the joint exceeds the yield strength of the two kinds of materials,and the peak stress at the interface of the TA2/Q345 clad plate is larger than that at the welding seam after subplate is welded.To ensure the safe operation of the clad plate components during service,the influence of welding residual stress on the bearing capacity,interface bonding strength and corrosion resistance was investigated.The effect of welding process on the baseplate,subplate and coverplate on the clad plate was discussed separately.The results show that the increase of preheating temperature and decrease of interlayer cooling time can effectively reduce the baseplate welding residual stress;the decrease on the arc power and interpass cooling time,the increase on welding speed,and the synchronous welding sequence along with the same direction can reduce the residual stress at the interface and weld surface of the coverplate,and increase the yielding rate as well.Due to the limit of the stress regulation of the clad plate for the single factor under the constraint condition of the joint,the regulation investigation of multi-factors was made for the welding process of the three regions.It is found that the load-carrying capacity of the baseplate is improved effectively at the preheating temperature of150°C and cooling time of 100 s.When the subplate is used,the minimum welding residual stress can be obtained at the cooling time of 100 s,the welding power of 450 W,the welding speed of 3.2mm/s accompanying the synchronous welding sequence along the same direction.At this case,the peak stress is reduced up to 21.3%,and the effect of the welding process of the subplate on the residual stress of the interface can be ranked as S>t>P>v.When the coverplate is welded,the optimum process is the combination of synchronous welding along the same direction,200/1000 s,1000W and 1.2mm/s.The peak equivalent stress can be reduced by 31%,the stress at the weld surface has the mimimum effect on the corrosion resistance,and their effect can be ranked in the order of S>t>v>P.The TA2/Q345 clad plate utilizing coverplate-lap with complex structure was welded using the optimized parameters by simulation,the weld pool morphology was characterized by the thermal cycle curve and stereomicroscope,and the residual stress was measured using the blind-hole method.It is found that the measured values are in good accordance with the calculation results,and the the tensile and shear properties can meet the actual requirements of the optimization process.更多还原