An Experimental Study of Rolled Friction-Stir-Welded Aluminum 6061-T6 Joints Subjected to Static and Fatigue Loading Con
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JMEPEG https://doi.org/10.1007/s11665-020-04949-w
An Experimental Study of Rolled Friction-Stir-Welded Aluminum 6061-T6 Joints Subjected to Static and Fatigue Loading Conditions S. Hassanifard, H.A. Reyhani, A. Nabavi-Kivi, and A. Varvani-Farahani (Submitted January 24, 2020; in revised form May 13, 2020) The present study attempts to examine monotonic and fatigue response of friction-stir-welded (FSW) Al 6061-T6 joints. Surface-rolling techniques of in situ and sequential were adapted to evaluate the influence of generated surface deformation on static and fatigue properties of the welded joints. A custom-made tool with four balls with the capability of changing in ball sizes and ball indentations was employed to burnish, while stir-weld beads are formed in situ. The sequential technique, however, rolled the top surface of joints after completion of welding operation. Tensile strength values measured from in situ-rolled FSW joints undergoing static loading were found to be, respectively, 25 and 40% higher with ball sizes of 6 and 8 mm as compared with those un-burnished FSW joints. Fatigue lives of in situ-rolled samples were also enhanced, respectively, 4 and 6 times in magnitudes for these ball diameters. Sequential rolling technique, however, resulted in a negligible elevation in static and fatigue properties of FSW joints. The in situ rolling process on the FSW samples led to more uniform and refined grains especially in HAZ region as compared with those of AW specimens. This resulted in higher static strength and longer fatigue lives. SEM images of the fractured surface revealed brittle fracture over crack initiation site followed by a mixed cleavage and ductile dimples at the rupture stage. Keywords
fatigue life, friction stir welding microhardness, microstructural features, rolling technique
(FSW), surface
1. Introduction Mechanical joining techniques such as welding and bolting have always been a field of interest for engineers. These techniques omit the need for making complicated parts in one single process of forging or casting while maintaining similar mechanical properties. These techniques offer temporary, permanent, and semi-permanent joining mechanisms. For decades, welding has been one of the most applicable permanent ways of joining components and structures. Conventional welding processes such as arc welding usually fail to weld a wide variety of aluminum-based alloys (Ref 1). The friction stir welding (FSW) technique, invented in the Welding Institute (TWI) in 1991 (Ref 2), is a primary solution for joining aluminum and magnesium alloys. The application of FSW can be found in various industries including aerospace, automotive, railways, shipbuilding and offshore (Ref 3). FSW is a joining mechanism while preserving low weight in the joint through excluding separate material as filler, the process offers nearly the same mechanical properties as the parent material. In-situ rolling FSW requires no extra process to (i) improve the surface
S. Hassanifard, H.A. Reyhani, A. Nabavi-Kivi, and A. Varvan
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