AZ31 Mg/5A05 Al脉冲冷弧MIG焊接头焊缝组织特性

Microstructures of Weld Seam in AZ31 Mg/5A05 Al Joint by Pulse Current Cold Arc MIG Welding

采用SAl5183焊丝对AZ31 Mg/5A05 Al异质对接接头进行脉冲冷弧MIG焊接,采用扫描电子显微镜、X射线衍射及万能力学试验机等对接头微观组织及拉伸力学性能进行研究。结果表明,采用脉冲冷弧MIG焊可以实现AZ31Mg/5A05 Al异质接头的无裂纹焊接。镁侧焊缝由镁母材至焊缝中部依次形成了α–Mg胞状晶、α–Mg+Al_(12)Mg_(17)羽状共晶、Al12Mg17树枝晶、Al_(12)Mg_(17)+A_(l3)Mg_(2)共析组织、颗粒状α–Al+Al_(3)Mg_(2)共晶和岛状α–Al+晶间Al_(3)Mg_(2)共晶等复杂结构;中部焊缝及铝侧焊缝主要为α–Al固溶体。焊缝的显微硬度分布不均匀,其中镁侧焊缝存在Mg–Al金属间化合物,显微硬度较高。在拉伸测试中,接头断裂于镁侧焊缝中,呈脆性断裂,最高抗拉强度可达93 MPa。

The pulse current cold arc MIG welding of AZ31 Mg/5A05 Al heterogenous butt joint is carried out by filling SAl5183 wire.The microstructures and tensile strength of the joint were studied by scanning electron microscope,X-ray diffraction and tensile test.The results show that crack-free AZ31 Mg/5A05 Al heterogeneous joints can be achieved by the operated welding process.Complex weld is formed near the magnesium side.α–Mg cellular crystals,α–Mg+Al_(12)Mg_(17) feather like eutectics,Al_(12)Mg_(17) dendrites,Al_(12)Mg_(17)+Al_(3)Mg_(2) eutectoid structure,granularα–Al+Al_(3)Mg_(2) eutectic structure,islandα–Al+intercrystalline Al3Mg2 eutectic structure are formed orderly from the magnesium base metal side to the middle of the weld.The mid-weld and the weld near aluminum side are mainly composed ofα–Al solid solutions.Nonuniform microhardness distribution across the weld is observed.The microhardness of the weld near the magnesium side is much higher than other regions due to the existence of Mg–Al intermetallic compounds.The fracture happened in the weld near magnesium side in the brittle fracture mechanism during the tensile test.The ultimate tensile strength of the joints reaches 93 MPa.