Research On Aluminized Layer Phase Of Gathering Pipeline Steel

NiTi alloy is a kind of new medical material developed in nearly twenty or thirty years, ithas been widely used in the field of interventional medical science(minimally invasive surgerymedical sciences). At present, the composition design and preparation of NiTi alloy productstechnology becoming mature, and has entered the practical stage, but the connection technologyof NiTi alloy has not being breakthrough, it has becoming a problem needs to be overcome. Thisarticle uses the pulse laser welding technology of NiTi alloy wire lap welding technology processand performance study, welding process parameters were analyzed by using orthogonalexperimental design (including: the working current, pulse width, frequency, defocus amount,protective gas flow rate, etc.)affect the performance of welded joint, welding of the welded jointby different process after the completion of the heat treatment after welding. By the means ofSEM and EDS analysis methods such as the analysis of the welded joint and heat treatment afterwelding on the influence of the welding joint organization morphology; With the analysis ofelectrochemical test, the corrosion of welding joint performance; By means of tensile test,fatigue test, the mechanical properties of welded joint are analyzed, and comparing with theparent metal, it is concluded that the possibility of pulsed laser welding process. The mainconclusions as follows:According to the orthogonal experiment, NiTi laser welding alloy wire should choose smallcurrent, pulse width, negative defocusing amount, at the same time using Ar gas protection;melting zone of laser spot welding joint is composed of dendrites, heat affected zone iscomposed of columnar crystal,parent material is composed of fine equiaxed grains; the numberof laser spot welding joints of the carbide obviously less than the parent material; joint tensilestrength and elongation rate is lower than the parent material; at room temperature, tensilestrength of parent material joint84%, residual strain joint and base metal is respectively1.8%and1.2%, the reason is due to the formation of joint performance of laser welding of columnarcrystal.The corrosion resistance of NiTi alloy laser welded group are better than that of base metal.Because of the small number of laser welding of inclusion, surface easy to form the passivation film of uniform, continuous, so as to improve the corrosion resistance of NiTi alloy. Under thesame conditions, the NiTi alloy microstructure of laser welding of the passivation potential rangethan the parent material, breakdown potential than the parent material of high.The laser welded NiTi has good superelastic fatigue property. In the loading and unloadingcycle, although initially residual strain than the parent material, but with the cycle numberincreasing, the residual strain tends to be stable.Have the effect of annealing temperature on properties of laser welded joints. With theincrease of annealing temperature, the tensile strength and the plateau stress decreased, theresidual strain. With increasing annealing time, yield stress and fracture strength decrease,residual strain decreases.