异种镁合金AZ31与NZ30K激光焊接接头分析

Analysis of Laser-Welded Joint of Dissimilar Magnesium Alloys AZ31 and NZ30K

为研究NZ30K稀土镁合金和AZ31镁合金的异种材料激光焊接,对采用CO2激光焊成的AZ31与NZ30K异种对接焊接头组织和性能进行了分析。在激光功率为4～5kW,焊接速度为4m/min时获得了成形良好的异种镁合金焊接接头。对获得的焊接接头进行了接头组织分析、焊缝区合金元素分布及析出相的分析及接头硬度和拉伸性能的测量。金相观察发现,异种镁合金激光焊缝是两种母材的熔合,在宏观上两种母材成分未完全混合在一起,且相应成分的组织区域呈波浪状夹杂态。X射线衍射(XRD)检测显示焊缝中存在α-Mg、Mg17Al12及Mg12Nd等相组织。扫描电镜(SEM)观察进一步显示了焊缝区存在着不同化学成分区域,焊缝晶粒显著细化。接头元素分布情况表明焊缝合金元素的分布由一侧熔合线至另一侧熔合线存在明显的浓度梯度。焊缝硬度不低于母材硬度;接头抗拉强度为169MPa,低于两种母材的抗拉强度。

In order to research laser welding of dissimilar magnesium alloys NZ30K and AZ31, the microstructure and property of the joint of AZ31 and NZ30K welded with a CO2 laser is analyzed. A sound weld is formed with the laser power of 4~5 kW and the welding speed of 4 m/min. The joint microstructure, the precipitated phase and weld element distribution are analyzed, the hardness and tensile strength of the joint are also measured. The optical microscope （OM） observation shows that the weld metal is a fusion of the two different alloys, which presents an incomplete mixture and the alloys interweave in wave-form with each other. By X-ray diffraction （XRD） analysis, a- Mg, Mg17 All2 and Mgl~ Nd phases are identified in the joint. The scanning electron microscope （SEM） shows further fine structure and regions of different chemical compositions in the weld. An obvious concentration gradient of alloying elements crossing the joint is observed too metal. The tensile strength of the joint is 169 MPa, The hardness of the joint is not lower than that of the base which is lower than those of the base metals.