Microstructure and mechanical properties of friction spot welded 6061-T4 aluminum alloy

Friction stir spot welding (FSSW) is a solid-state metal joining process derived from friction stir welding. In this study, FSSW of AA5052-H32 and AA6082-T6 dissimilar aluminium alloys are performed at three different tool rotations specifically 1500, 1070, and 765 rpm. The other process parameters such as tool design, tool tilt angle, plunge depth, and axial force were held constant to investigate the effect of tool rotation on FSSW of dissimilar AA5052-H32 and AA6082-T6 alloys. Microstructural characterization and mechanical testing were carried out to evaluate the properties of weld joints. Microstructural examinations confirmed defect-free samples for all three tool rotation, while microindentation hardness and tensile-shear tests reported enhanced ultimate tensile strength as a mechanical property for high tool rotation speed of 1500 rpm.

Effect of Tool Rotation Speed on Friction Stir Spot Welded AA5052-H32 and AA6082-T6 Dissimilar Aluminum Alloys

SPOT FRICTION WELDING OF HIGH-STRENGTH SHEET STEEL Jack Hunter Sederstrom School of Technology Master of Science Spot friction welding (SFW) was performed on ultra high strength steel (UHSS) steel sheet commonly used in automobile manufacturing. Alloys studied included DP780, DP780EG, DP980, and DF140T sheet steel of varying thickness from 1.2 mm to 1.4 mm. Welding was accomplished using a PCBN standard tool. Weld strengths were then compared to a proposed AWS standard. Initial hardness readings were taken in cross sectioned samples. Grain structure in a SFW is presented. Resistance spot welds were created in three steels. This study focuses on the strength of SFW joints as compared to traditional resistance spot welding (RSW) in welding like materials to one another. Cycle times of SFW were also evaluated and compared to production rate cycle times of RSW.

/pdf/spot-friction-welding-of-ultra-high-strength-automotive-1aodmsurqi.pdf

Spot Friction Welding of Ultra High-Strength Automotive Sheet Steel

The key to improve the strength of Al/steel dissimilar joint is to toughen the hard and brittle interfacial intermetallics. Introducing soft and tough dispersions into the interfacial intermetallics would be a promising method. In the present study, Zn-Al alloy (Zn-22Al) was used as the filler metal to generate dispersions in the interfacial intermetallics matrix of dissimilar laser Al/steel joint. The results have shown that soft and tough dispersions, i.e., FeZn10, Al-rich amorphous phase, and Zn solid solution, were successfully introduced into the hard and brittle Fe2Al5−xZnx matrix. The formation of these dispersions was resulted from diffusion of elements Fe and Al and infiltration of liquid Zn along the grain boundaries of Fe2Al5−xZnx matrix and the subsequent chemical reaction and solidification. With this kind of interfacial microstructure, the joint exhibited a stable peak fracture load of 1200 N even though the interfacial layer thickness increased from 20 to 45 μm. This was because the interfacial layer was toughened by the soft and tough dispersions. Using this example, introduction of soft and tough dispersions into hard and brittle intermetallics matrix to toughen interfacial layer and then strengthening of dissimilar joints will be highlighted.

Formation and Toughening Mechanisms of Dispersions in Interfacial Intermetallics of Dissimilar Laser Al/Steel Joints

Friction stir spot welding (FSSW) is a type of solid state joining processes, which was derived from the linear friction stir welding (FSW) as an alternative method for single-point joining processes like resistance spot welding and fastening. The main limitation of FSSW is the keyhole that remains at the center of the spot after welding process, which can be classified as a defect for the friction stir spot welding in its conventional method. In this work, a newly developed technique called friction stir spot welding with refilling by friction forming process (FSSW-FFP) was used to remove the keyhole from the conventional FSSW joints. Both of this new technique and conventional friction stir spot welding process were used to weld lap shear specimens of AA2024-T3 aluminum alloy sheets, thickness 2 mm, and the results were compared. Two types of tool pin geometry (straight cylindrical & triangular) and three rotational speeds (535, 980, and 1325) rpm were used to study the effect of these parameters on the mechanical and microstructural properties of friction stir spot welds. The keyhole was successfully refilled by the new refilling process. The tensile-shear test results showed that the refilled FSSW specimens are better than the specimens welded by the conventional FSSW process at all tool rotational speeds with using different tool pin profiles. The minimum tensile shear load obtained from the conventional friction stir spot welds was improved (to about 45%) by the refill FSSW process. Fracture modes under tensile shear tests were analyzed in detail using the scanning electron microscope (SEM). The variation of microhardness in different regions of the spot was evaluated.

/pdf/effects-of-rotational-speeds-and-tool-pin-geometry-on-2zv003t27y.pdf

Effects of Rotational Speeds and Tool Pin Geometry on Microstructure and Mechanical Properties of Refilled Friction Stir Spot Welds of Similar AA2024-T3 Aluminum Alloy Sheets

Friction stir spot welding of aluminum alloys

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Friction stir spot welding of aluminum alloys