LZ91镁-锂合金TIG焊接接头组织与性能的试验研究

Experimental research on the microstructure and mechanical properties of LZ91 Mg-Li alloy TIG welded joint

采用交流钨极氩弧焊(TIG)对2 mm厚LZ91镁-锂合金板材进行了焊接,焊材成形性能良好。采用OM、XRD、SEM分析了焊材和母材的显微组织,通过拉伸试验、硬度测试分析了焊材的力学性能。焊材由焊缝、热影响区、母材区组成。焊缝区、热影响区较宽,分别约为8 mm、6 mm。受焊接热效应及降温速率影响,三个部分相组织明显不同,焊缝区内α相为胞状枝晶随机地均匀分布在β相内;热影响区内β相为粗大的等轴晶,晶粒尺寸与到焊缝的距离呈反比,α相呈针状或条带状,相含量与到焊缝的距离呈正比;母材区为典型的轧制退火态组织。硬度:热影响区的最高,母材的次之,焊缝区的最低。焊材在焊缝区断裂,抗拉强度为169.61 N/mm2,达到母材抗拉强度的95.6%。伸长率为21.4%,为母材的77.5%。焊接后,断裂方式由解理断裂转变为韧性断裂。

The material with well performance used in this experiment, 2 mm thick weld material of LZ91 magnesium lithium alloy, is achieved by the alternating current tungsten arc welding （AC-TIG）. The performance of welding fabrication and microscopic structure of welded joints are studied by utilizing OM, XRD and SEM. Mechanical properties of welded joints are analyzed through the tensile experiment and Vickers hardness test. Affected by AC-TIG,the weld material consists of weld-joint area （ -8 mm）, heat affected area （ ~ 6 mm） and base metal. Due to different heat effects and cooling rates, quite different micro- structures are achieved in three areas. In the weld-joint area, cellular dendritic-like at phases are uniformly dispersing in arbitrary directions within the 13 phase matrix. In the heat affected area, β phases are coarse equiaxed crystals and the grain size is inversely proportional to distance to the welding joint. The content of needle-or-strip-like α phase is proportional to distance to the welding joint. In the base metal exists the typical structure of rolling plates.