AZ31B/AZ91D异种镁合金激光焊接头组织性能分析

Analysis of laser welded joint of microstructure and mechanical properties of dissimilar magnesium AZ31B and AZ91D

针对AZ31B和AZ91D异种镁合金材料的激光焊接问题,通过光学显微镜、拉伸试验、显微硬度测试等手段分析研究AZ31B和AZ91D异种镁合金CO2激光焊接头组织性能。结果表明:在功率为1 800 W,焊接速度为600mm/min,保护气流量为15L/min时,可以获得成形良好的焊缝。对焊接接头微观组织进行分析发现,接头热影响区不明显,熔合线附近母材侧晶粒未发生明显长大,焊缝晶粒明显细化;通过XRD检测可知焊缝区主要由α-Mg和β-Al12Mg17这2相组成;通过EDS能谱分析得到焊缝区Mg、Al元素的质量分数介于2种母材之间;通过拉伸试验发现,断裂位置位于AZ91D母材上,焊接接头抗拉强度高于AZ91D母材,扫描断口显示断裂方式为脆性断裂;焊缝硬度高于2种母材硬度。

Studies on the microstructure and properties of dissimilar magnesium AZ31B and AZ91D joints welded by CO2 laser using optical microscope,tensile test,microhardness test and etc are presented.The results show that a sound weld can be ob-tained with a laser power of 1 800 W,a welding speed of 600 mm/min and a flow rate of shielding gas of 15 L/min.Analysis of microstructure of welded joint shows that the heat affected zone is not apparent,the growth of the grains in base metal close to the fusion line are not obvious,and the grain size in weld is refined.X-ray diffraction shows that there areα-Mg andβ-Al12 Mg17 phases in the welded zone.EDS analysis shows that the element’s content of Mg,Al in the welded zone are between that of the base metal AZ91D and AZ31B.Tension results show that the fracture is mainly happened on AZ91D,which indicates that the tensile strength of joint is higher than the base metal AZ91D,and the dominant fracture mechanism is brittle fracture.The hard-ness of welded zone is higher than two base metals.