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研究了深冷处理对镁合金焊接接头疲劳性能影响。采用TIG焊接AZ31B镁合金,在-160℃、保温12 h深冷工艺下对镁合金焊接接头进行深冷处理。测试未深冷组和深冷组镁合金焊接接头疲劳性能,用最小二乘法拟合实验数据得到S-N曲线,计算2×106循环次数下,未深冷接头疲劳性能为36.42 MPa,深冷接头疲劳性能为41.26 MPa,深冷处理后接头疲劳强度提高13.29%。用盲孔法分别测试未深冷和深冷后垂直焊缝不同位置的残余应力。结果表明:深冷处理后焊接残余应力下降;深冷处理后焊缝晶粒比未深冷焊缝晶粒明显细化。未深冷接头疲劳断口为解理断裂,深冷后接头疲劳断口为韧性断裂,说明深冷处理可提高焊接接头韧性。深冷处理可以提高镁合金焊接接头疲劳性能。
The effect of cryogenic treatment on the fatigue properties of magnesium alloy welded joints was studied. Magnesium alloy TIG welding AZ31B magnesium alloy at -160 ℃, 12 h insulation process of magnesium alloy welded joints cryogenic treatment. The fatigue behavior of the welded joints of non-cryogenic and cryogenic groups was tested. The SN curves were obtained by fitting the experimental data by the least square method. The fatigue performance of the cryogenic joints was 36.42 MPa at 2 × 106 cycles, The performance is 41.26 MPa, the fatigue strength of the joint after cryogenic treatment is increased by 13.29%. The residual stress in different positions of the vertical weld after not cryogenic and cryogenic tests were respectively tested by blind hole method. The results show that the welding residual stress decreases after cryogenic treatment. The grain size of the weld is significantly refined than that of the cryogenic weld after cryogenic treatment. The fatigue fracture of the subcooled joint is the cleavage fracture, and the fatigue fracture of the joint after cryogenic fracture is the ductile fracture, which indicates that the cryogenic treatment can improve the toughness of the welded joint. Cryogenic treatment can improve the fatigue performance of magnesium alloy welded joints.