激光焊接镁/铝异种金属的显微组织与性能

Microstructure and mechanical properties of magnesium/aluminum alloy laser welding

摘要:

对1.8mm厚AZ91镁合金和1.2mm厚6016铝合金平板试件进行激光搭接焊试验，利用体视显微镜、卧式金相显微镜、扫描电镜、X射线衍射仪、电子显微硬度仪、微机控制的电子万能试验机等手段研究了镁/铝焊缝的表面成形性、接头区域的金相组织、界面元素分布、断口形貌、主要物相、显微硬度与接头力学性能。结果表明：激光功率1900W，焊接速度50mm/s，离焦量0mm，Ar气为保护气体且流量为15L/min的条件下，焊缝表面成形性良好，热影响区窄，晶粒细化；焊接接头平均抗拉强度和抗剪强度分别为13.99 MPa和12.79 MPa，镁侧和铝侧焊缝硬度均高于母材；剪切断口较平坦、光滑，出现相互平行的疲劳条纹；拉伸断口存在较多高度不一致的解理台阶，呈脆性断裂特征；镁/铝焊缝界面存在Mg17Al12、Mg2Al3主要物相，其中Mg17Al12脆性相高温下比Mg2Al3延性相结构稳定，是镁/铝焊接接头呈现脆性特征和较难实现焊接的主要原因。

Abstract:

The laser welding test was carried out on AZ91 magnesium alloy with thickness 1.8 mm and 6016 aluminum alloy with thickness 1.2 mm. By using optical microscopy, horizontal microscope, scanning electron microscopy, X-ray diffraction, electron micro-hardness and tensile test, the weld surface morphology, microstructure, interface element distribution,fracture morphology, main phase,hardness and mechanical properties of joints were studied. The results indicate that the morphology of welding surface can be improved, heat affected zone is narrow and grain size is fine when the welding power is 1900 W, welding speed is 50 mm/s, the defocus distance is 0 mm, and Ar gas acts as the protection gas with flow rate 15 L/min. The average tensile and shear strength of the welding sample reaches 13.99 MPa, 12.79MPa, respectively.The hardness in magnesium and aluminum side is both higher than that of the based material, shear fracture is relatively flat and smooth, parallel fatigue crack appears.Tensile fracture has more cleavage step with brittle fracture characteristics. The main phase,such as Mg17Al12, Mg2Al3, can be found in magnesium and aluminum weld interface, Mg17Al12 brittle phase is stable than that of Mg2Al3 with ductility at high temperatures, which lead to the welded joints brittle and is difficult to realize the welding between magnesium and aluminum.