The Effect Of Z-axial Force On Structure And Mechanical Property Of Al/Mg Dissimilar Friction Stir Welding Joint

The composite structure of Al/Mg dissimilar metals can not only satisfy the flexibility of industrial design,but also give full use of the excellent properties of the two metals.The connection between the two metals has attracted many attentions.Friction stir welding(FSW)is a new material solid state welding process invented by The Welding Institute(TWI)in 1991.Since the low heat input during the welding process can effectively avoid defects,appeared during fusion welding.Through change of Z-axial force,the thesis completed two series of welding experiments.At the same time,different microstructures at the Al/Mg interface were obtained by grinding the joints.According to the analysis of structure and mechanical properties of joints,exploring the effect of Z-axial force on the microstructure and properties of the joint,contribution of each microstructure of interface to tensile strength and influence of morphology and distribution of intermetallic compounds on the properties of joints were obtained.Research results suggest that Al/Mg interface and severely deformed zone are the weak areas of the joint.With the increase of Z-axial force,the heat input in the welding process is increased,leading to the excessive mixing of Al/Mg,resulting in thickening of intermetallic compound layer at the interface or the occurrence of irregular structure appears in severely deformed zone,which reduces the joint performance.For the upper structure,mechanical occlusal is the main feature,which is that the matrix crosses the original interface and enters the other side.The thickness of the upper part of zigzag line determines the strength of the structure.For the middle structure,metallurgical bonding is dominant,and is mainly composed of intermetallic compound layers.The thickness of intermetallic compound layer affects the strength of the structure.For the bottom structure,the strength mainly depends on the plunge depth and heat input during the welding process.Under different Z-axial force conditions,the morphology and distribution of intermetallic compounds will change and resultant mechanical property of the welding joints.