Study Of Using Biaxial Prestressing To Control Welding Distortion And Prevent Hot Cracking

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.