AZ31B镁合金TIG焊接件应力腐蚀性能研究

Research on the Properties of Stress Corrosion Cracking for Tungsten Inert-Gas Arc Welded AZ31B Magnesium Alloy

为了研究AZ31B镁合金钨极氩弧焊接件应力腐蚀性能,室温下采用三点加载的方式,在去离子水中对试样进行应力腐蚀试验。利用光学显微镜(OM)观测试样微观结构,利用扫描电镜(SEM)观测应力腐蚀断口,利用X-350A型X射线应力仪和CHI660B型电化学工作站分别测定试样表面残余应力和动电位极化曲线。试验结果表明:采用单面焊双面成型工艺,在45～50A的焊接电流及合适的焊接速度条件下,焊接2.2mm厚AZ31B镁合金薄板时,钨极氩弧焊能够获得理想的焊接接头,抗拉强度达到209MPa;焊接件热影响区表面残余拉应力为60MPa;同母材相比,焊接件自腐蚀电位减小27mV,腐蚀电流增大了41.4%,从而增加焊接件腐蚀倾向;AZ31B焊接件在去离子水中浸没192h后出现应力腐蚀开裂,属于穿晶型脆性断裂,这表明AZ31B镁合金焊接件在去离子水中具有很高的应力腐蚀敏感性。

In order to study the properties of the stress corrosion cracking （SCC） for the tungsten inert-gas （TIG） arc welded AZ31B magnesium alloy sheets, the SCC susceptibility of the welded samples was assessed by three points loading method in deionized water at room temperature. The microstructure of specimens and fracture surfaces were analyzed by OM and SEM, respectively. Surface residual stress and potentiodynamic polarization behaviors of the welded samples were examined by using X-ray diffraction technology and a CHI660B electrochemical workstation, re- spectively. The results show that when TIG arc welding was used to weld AZ31B Mg alloy plates with the thickness of 2.2 mm by using single-side welding double-side molding process, the ideal welding joints can be obtained at the welding current range from 45 A to 50 A and appropriate welding speed, the ultimate tensile strength of the welded joints is 209 MPa; The residual tensile stress is 60 MPa in the surface of heat effected zone of the welded joints; corro sion potential decreased by 27 mV and corrosion current increased by 41.4% compared to the base samples, which in- dicates the corrosion trend of the welded samples is increased; SCC appeared on the welded samples after 192 hours of immersion, the mode of fracture belongs to intergranular and brittle cracking, which shows higher SCC susceptibility of the TIG welded AZ31B in deionized water.