Fatigue behaviour of AA6082-T6 MIG welded butt joints improved by friction stir processing

Abstract

Friction Stir Processing (FSP) was based on the principles of Friction Stir Welding (FSW), a solid-state joining process originally developed for aluminium alloys. It is an emerging metalworking technique which can provide localized modification and control of microstructures in near-surface layers of processed metallic components. In this research, FSP appears as an alternative to traditional methods for fatigue strength improvement of weld joints, such as re-melting, hammering and blasting,. This technique was applied on Metal Inert Gas (MIG) butt welds with and without reinforcement, performed on AA 6082-T6 alloy plates. The potential benefits of post-processing MIG welds by FSP were studied using microstructure analysis, hardness measurement, tensile strength, residual stress measurement, and fatigue testing. Fatigue tests were carried out under constant amplitude loading with the stress ratio R set to 0. Friction stir processing of MIG welds does not change the hardness and mechanical strength of the weld substantially, but the fatigue strength was increased, due to the geometry modification in the weld toe, reduction of weld defects and grain refinement of the microstructure.

Fatigue of Friction Stir Welded Aluminum Alloy Joints: A Review

“…Specimens for fatigue test are usually sectioned and loaded perpendicular to the joint centerline [21][22][23][24][25][27][28][29][30][31]. Zhang [32] studied the fatigue fracture surface for a 6005 aluminum alloy FSW joint by Philips X130 SEM.…”

Effects of Microstructural Modification Using Friction Stir Processing on Fatigue Strength of Butt-Welded Joints for High-Strength Steels

“…For example, Costa et al [10] [11] [12] [13] reported that grain refinement and stress concentration reduction due to FSP at the weld toe increased fatigue strength of several aluminum alloy joints fabricated by metal inert gas welding.…”

Fatigue performances of FSW and GMAW aluminum alloys welded joints: Competition between microstructural and structural-contact-fretting crack initiation

“…As far as cyclic stresses are concerned, welding defects inherent to the GMAW process are prone to crack initiation, which significantly reduces the fatigue performance of welded assemblies as compared to the base material 9,13 . Specifically, da Silva et al 14 reported that fatigue cracks initiate at the weld toe (i.e., at the interface of the welding pass and the HAZ) due to the combined effects of higher porosity, lack of wetting, and change of geometry due to the filler material reinforcement, resulting in high stress concentration in the toe weld region 9,14 .…”