Influence of tool geometry and rotational speed on mechanical properties and defect formation in friction stir lap welded 5456 aluminum alloy sheets

Abstract

Friction stir welding of AA5456 aluminum alloy in lap joint configuration is with two different tempers, T321 and O, and different thicknesses, 5mm and 2.5mm was investigated. The influences of tool geometry and various rotational speeds on macrostructure, microstructure and joint strength are presented. Specifically, four different tool pin profiles (a conical thread pin, a cylindrical-conical thread pin, a stepped conical thread pin and Flared Triflute pin tool) and two rotational speeds, 600 and 800 rpm, were used. The results indicated that, tool geometry influences significantly material flow in the nugget zone and accordingly control the weld mechanical properties. Of particular interest is the stepped conical threaded pin, which is introduced for the first time in the present investigation. Scanning electron microscopy investigation of the fracture location of samples was carried out and the findings correlated with tool geometry features and their influences on material flow and tension test results. The optimum microstructure and mechanical properties were obtained for the joints produced with the stepped conical thread pin profile and rotational speed of 600 rpm. The characteristics of the nugget zone microstructure, hooking height, and fracture location of the weld joints were used as criteria to quantify the influence of processing conditions on joint performance and integrity. The results are interpreted in the framework of physical metallurgy properties and compared with published literature.

Friction stir lap welding of 5456 aluminum alloy with different sheet thickness: process optimization and microstructure evolution

“…Of special interest is also the work of Fujii et al [12] on the effect of tool geometry on mechanical and microstructural properties of friction stir welded 1050-H24, 6061-T6, and 5083-O aluminum plates. Recently, the present authors [18] showed that a stepped conical threaded pin gives more homogeneous and defect free joints.…”

“…Indeed, during FSW lap welding, the material of the lower plate is pushed up toward the upper one [19]. amount of plastic deformation and centrifugal forces than the one in the lower plate [18]. As a result, the stir zone in the upper plate has a more uniform structure and consequently similar hardness.…”

“…These types of joints are commonly used for assembling different structural components in transportation industry such as ship decks, walls, railway tankers and wagons [3,4,18,20]. The data 5 becomes even less available when dissimilar welding conditions (material thickness or conditions) are considered [18].…”

“…The data 5 becomes even less available when dissimilar welding conditions (material thickness or conditions) are considered [18].…”

Multi-Track Friction Stir Lap Welding of 2024 Aluminum Alloy: Processing, Microstructure and Mechanical Properties

“…It is clear from the macrographs that obvious defects are observed in the samples at most process parameters. Actually, FSLW was developed based on the principle of FSW, and FSW has been widely found to have the characteristic of narrow parameter range [16][17][18][19][20]. For the current case, it is more difficult to produce high-quality welds by FLSW compared with the widely studied friction stir butt welding.…”