Abstract
The trend in welding of dissimilar aluminum alloys oriented to new application techniques to increase the functionality and perform the welding procedure without any problem in the welded joints. The pin profile and process parameters determined for the friction stir welding greatly affect the weldability and strength of the welded joints. In addition, it is also considered that the pin offset is also an effective factor on the strength and microstructure of welded joints. In the present study, aluminum alloys AA 6013–T6 and AA 7075–T651 were welded with the FSW process applying pin offset technique. The changes in the mechanical and microstructural properties were investigated. The onion ring structure was observed in all of microstructure of weld stir zone. Except the welded joint fabricated with the tool rotational speed of 400 rpm for both without pin offset and with offset to retreating side, all the welded joints were fractured at the base metal region and heat affected zone in AA 6013 alloy. The welded joints fabricated with the tool rotational speed of 400 rpm consisted of small and large cavity-type defects. Although defects were found to occur in the welded joints, none of the welded joints were fractured at the SZ during the tensile and bending tests. The ultimate tensile strength and elongation at rupture of the dissimilar FS welded joints were ranged between 164 MPa and 179 MPa, 6.5 and 7.6%, respectively. These defects were found to affect the ductility feature of the welded joints. The pin offset direction was found to affect the volume of parent materials in the stir zone. Hence, the material volume in the onion rings changes and, the hardness distribution is also affected by the changes in the material volume. Keywords: aluminum alloys, friction stir welding parameters, fracture analysis
Highlights
Friction stir welding (FSW) is one of the most important solid state welding technique and has attracted attention in the welding of dissimilar materials in recent years
The results were evaluated : 3.1 Macrostructural evaluations Figure 3a shows the macrographs of the cross section of each FS welded joints consisting of heat affected zone (HAZ), thermo mechanically-affected zone (TMAZ), stir zone (SZ)
Sharma et al [22] reported that onion rings exhibit alternates bright and dark rings and those rings are formed due to the flow of the material in batches occurred by rotating movement of the tool and extruding of the plasticized material in the form of semi cylindrical layer in one rotation
Summary
Friction stir welding (FSW) is one of the most important solid state welding technique and has attracted attention in the welding of dissimilar materials in recent years. The FSW process presents superior advantages in comparison to those of conventional fusion welding techniques in achieving sound welded joints [1,2]. Mismatch problem between the dissimilar materials, solidification or liquation cracking, formation of porosity, segregation and dendritic structure are eliminated, as well [3]. Solidification cracking in aluminum alloys is accepted as the critical issue due to the consistency between the filler materials and base materials [4]. Some of aluminum alloys used in those industries need special care during the welding process. Fusion welding of the dissimilar materials is difficult in comparison to welding of similar materials. The FSW process occurs in the solid phase of the materials, eliminating most of the problems occurred in the fusion welding
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