中文摘要：

对AZ31镁合金及其焊接接头进行拉伸、冲击和疲劳试验，分析了镁合金的断裂机理及疲劳裂纹扩展方向。母材拉伸试验结果表明，试样几乎没有缩颈，抗拉强度为236．29MPa；焊接接头的抗拉强度为185．68MPa，拉伸断裂从焊接接头焊趾部位启裂，抗拉强度为母材的78％。冲击试验在-80～340℃进行，结果表明，在较低温度下AZ31镁合金冲击韧性较小，断口为准解理形貌的脆性断裂；随着温度的增加，断裂形式由准解理＋韧窝形貌的混合断裂过渡为韧性断裂；在常温下焊缝中心的冲击韧性比母材的高，但热影响区的冲击韧性较差。AZ31B镁合金母材的疲劳强度为66．72MPa，对接接头的疲劳强度为39．00MPa；母材疲劳断口由解理台阶组成，为脆性断裂；焊接接头疲劳断口由解理和准解理台阶组成，为脆性断裂。

英文摘要：

Tension test, impact test and fatigue test were carried on for AZ31 magnesium alloy and its welding joint; fracture mechanism and crack propagation direction were analyzed. Base metal tension test results indicate that there is nearly no necking-down in tension specimen and the tension failure is brittle fracture; welding joint tension test results indicate that crack initiation position is in the weld, tensile strength of welding joints is 78% of the base metal＇s. Impact test was tested in -80-340 ℃ range, and the results indicate that AZ31 magnesium alloy impact absorbing energy is relatively little at low temperature, the fracture is brittle fracture based on quasi-cleavage fracture; with increase of temperature, fracture mode transits from mixed mode fracture based on quasi-cleavage ＋ dimple to toughness fracture. The fatigue strength of the AZ31B magnesium alloy base metal and the butt joint was 66.72 and 39.00 MPa respectively. Base metal fatigue fractures consist of cleavage plane, and it was brittle fracture. Welding joint fatigue fracture consists of quasi-cleavage and it was brittle fracture.