异种铝合金搅拌摩擦焊搭接接头的显微组织与硬度研究

Microstructure and Microhardness of Friction Stir Welded Lap Joint of Dissimilar Aluminum Alloy

采用搅拌摩擦焊对异种铝合金6061-T6(上板)和A356-T6(下板)进行搭接焊,用体式和光学显微镜观察搭接接头的组织形貌,并测试其显微硬度。结果表明:在适当的工艺参数条件下,可以获得表面成形良好、内部无明显缺陷的搭接接头。在焊核区,两板间存在明显的界面,且位置较原位置整体上移,前进侧界面处呈锯齿状,界面由两种铝合金组织交替镶嵌而成,而后退侧界面则呈曲线状。两板均呈现典型的搅拌摩擦焊接头组织:焊核区由细小的等轴晶组成,而热影响区组织与母材相似,晶粒有细微粗化,热机影响区晶粒被拉长、弯曲,有明显的塑性流动。两板焊缝区显微硬度比各自母材均有不同程度的降低,且上板6061-T6降低幅度较大,焊后最大硬度约为母材的65%。

The microstructure of friction stir welding lap joint between 6061-T6（upper） and A356-T6（lower） was observed by optical microscope,the microhardness of the welded joint was tested.The results show that the joint has well-shape and no obvious defects under the appropriate process parameters.In the weld nugget zone,there is a distinct interface between two plates.Compared with the original position,the position of the interface is higher.Tag appears at the advancing side of interface,which consists of two aluminum alloy microstructure alternating.However,the interface at back side looks like curve shape.Both of two plates show typical microstructure of FSW： the weld nugget zone is composed of fine equiaxed grains;the heat affected zone microstructures are similar to base material,and the grain coarses slightly;the grain in thermo-mechanical affected zone is stretched and bent with a clear plastic flow.The microhardness of two plates in the welding zone decreases in different degree compared with base material,and the upper plate of 6061-T6 is worse,whose highest hardness after FSW is about 65% of the base material.