【作者】 赵耀邦；

【导师】 刘雪松；

【作者基本信息】 哈尔滨工业大学 ， 材料加工工程， 2007， 硕士

【摘要】 焊接变形大和热裂敏感性高是铝合金薄板结构焊接加工中存在的较为严重的问题。基于焊接变形和热裂纹的产生都与焊接过程中的应力应变演变密切相关,本文从力学角度出发,首次提出双向预置应力控制焊接变形和防止热裂纹新工艺,同时解决了焊接变形和热裂纹问题。预置纵向拉应力控制焊接变形和降低焊接残余应力,与此同时预置横向压应力抵消焊缝金属固有的凝固收缩时受到的拉应变以及预置纵向拉应力对焊缝金属造成的额外拉应变,从而起到防止热裂纹的作用。采用有限元数值模拟和工艺试验相结合的研究方法,首先模拟了双向预置应力下的静力学应力应变场,然后模拟了双向预置应力作用下焊接过程中的应力演变过程和焊后残余应力。模拟结果表明了双向预置应力控制焊接变形和防止热裂纹工艺的可行性,研究了预置纵向拉应力和横向压应力这两个重要参数对其作用效果的影响以及交互作用,初步揭示了其作用机理,并为工艺试验中制定合理的工艺参数提供指导。自主设计制造了双向预置应力焊接机构,在此基础上针对尺寸为300mm×200mm×2mm的LY12CZ铝合金进行了双向预置应力焊接工艺试验。试验结果表明:预置横向压应力保持0.2σs不变时,随着预置纵向拉应力的增加,焊接挠曲变形量越来越小,从常规焊时的最大挠曲变形量的13mm下降到预置纵向拉应力为0.7σs时的2mm,同时焊接残余应力峰值从常规焊时的213.4MPa下降到41.6MPa;随着预置纵向拉应力的增加焊接热裂纹的倾向有增大的趋势,施加横向压应力能很好的解决预拉伸控制焊接变形中出现的热裂纹问题,在施加0.5σs预置纵向拉应力而无预置横向压应力时热裂纹率高达13.4%,而施加0.3σs预置横向压应力后基本上无宏观热裂纹的出现;预置横向压应力对焊接变形的控制也起到一定的作用,但是预置横向压应力值较小时,其作用有限;用0.6σs～0.7σs的预置纵向拉应力配合0.2σs～0.3σs的预置横向拉应力时,得到了低应力、小变形且无焊接热裂纹的试件。更多还原

【Abstract】 Welding distortion and high susceptibility to hot cracking are serious problems associated with welding thin plate structures of aluminum alloys. Considering that both welding distortion and hot cracking are relative to the evolution of stress and strain in the welding process, a new technology named biaxial prestressing method is put forward to control the welding distortion and prevent welding hot cracking from the view of mechanics. The longitudinal prestressing is used to control welding distortion and reduce residual stress; at the same time exerting transverse plastic compression strain on the weld through the transverse prestressing counteracts the tensile strain which leads to hot cracking.Both finite element simulation and engineer testing are applied to study the problem. First of all, the static stress and strain fields which are caused by the biaxial prestressing are simulated. Then, the evolution of stress and residual stress in the welding process are simulated. The simulation result has proved the feasibility of biaxial prestressing method and has discovered the basic mechanism. Moreover, the simulation results help to establish the proper parameter of engineer testing.The valid equipment of biaxial prestressing method is designed and manufactured. In the welding test and study, the size of 300mm×200mm×2mm of LY12CZ aluminum alloy thin plates are employed. The conclusions above can be got from the experiment result: the maximum deflection deformation tends to decrease with the increasing of the longitudinal prestressing when the transverse prestressing is constant, the maximum deflection deformation in conventional welding is 13mm compared to the only 2mm in the biaxial prestressing method welding. At the same time, the maximum residual stress decreases from 213.4MPa to 41.6MPa. The hot cracking susceptibility is gradually increasing with the increasing longitudinal prestressing. however, The hot cracking susceptibility is gradually reduced with the increasing of the transverse prestressing, when the longitudinal prestressing is 0.5σs, the hot cracking rates is as high as 13.4% without transverse prestressing compared that there is nearly no macroscopical hot cracking when the transverse prestressing is 0.3σs. Transverse prestressing can also make a little effect on controlling welding distortion. When the longitudinal prestressing is about 0.6σs to 0.7σs and the transverse prestressing is about 0.2σs to 0.3σs, we can get the better weldment with low welding distortion and no hot cracking.更多还原