Mg-9.8Li-2.9Al-Zn合金激光焊接接头组织与力学性能研究

Microstructure and Mechanical Property of Mg-9.8Li-2.9Al-Zn Alloy Laser Welded Joint

采用CO2激光焊接2mm厚Mg-9.8Li-2.9Al-Zn合金,通过光学显微镜(OM)、扫描电镜(SEM)系统研究焊接接头成形、气孔裂纹缺陷、显微组织演变,并采用显微硬度测量和纵向拉伸测试焊接件的室温力学性能。结果表明,激光快速加热焊缝组织明显细化,α-Mg相增多且由母材的粗大组织转变为细针状组织,亚稳定的MgLi2Al相分解为稳定的AlLi相。焊缝的显微硬度(约105HV)高于母材的显微硬度(约85HV),对焊接件纵向拉伸断裂于母材,断裂后屈服强度Rp0.2为172MPa,伸长率约为24%。

The welding property of Mg-9.8Li-2.9Al-Zn alloy with the thickness of 2 mm using the CO2 laser is investigated. The joint forming, weld defects and structural evolution are studied with optical microscope （OM） and scanning electron microscope （SEM）. The mechanical property of the weldment is tested using the microhardness and longitudinal tensile test at room temperature. The result indicates that the rapid cooling during the laser welding results in the fine microstructures with more a-Mg phase in the weld, compared with that in the base metal. The metastable phase MgLi2Al transforms into the stable phase AILi. The weld microhardness （about 105 HV） is bigger than that of the base metal （about 85 HV）. The longitudinal tensile test of the weldment shows the fractured location along the base metal with the reference yield strength of 172 MPa and the percentage elongation after fracture of about 24 %.