Abstract
Friction stir welding (FSW) is an attractive solid-state joining technique for lightweight metals; however, fatigue properties of FSWed metals are lower than those of bulk metals. A novel mechanical surface treatment using cavitation impact, i.e., cavitation peening, can improve fatigue life and strength by introducing compressive residual stress into the FSWed part. To demonstrate the enhancement of fatigue properties of FSWed metal sheet by cavitation peening, aluminum alloy AA5754 sheet jointed by FSW was treated by cavitation peening using cavitating jet in air and water and tested by a plane bending fatigue test. The surface residual stress of the FSWed part was also evaluated by an X-ray diffraction method. It was concluded that the fatigue life and strength of FSWed specimen were improved by cavitation peening. Whereas the fatigue life at σa = 150 MPa of FSWed specimen was about 1/20 of the bulk sheet, cavitation peening was able to extend the fatigue life of the non-peened FSW specimen by 3.6 times by introducing compressive residual stress into the FSWed part. This is the first paper to demonstrate the improvement of fatigue properties of FSWed metallic sheet by cavitation peening.
Highlights
Friction stir welding (FSW) was invented at The Welding Institute (Cambridge, UK) [1,2]
To show the plastic pits pits produced by the cavitating jet in air, Figure 6 reveals the magnified aspect of deformation the produced by the cavitating jet in air, Figure reveals the magnified aspect of the welded welded side surface of Friction stirwelded welded (FSWed) AA5754 treated by (a) cavitating jet in air and (b) cavitating surface
To demonstrate the effect of cavitation peening on fatigue properties of metal sheet
Summary
It was reported that shot peening and laser peening could introduce compressive residual stress into the FSWed part [28,29,30,31,32]. Shot peening and laser peening are referred to as mechanical surface treatment, as local plastic deformation introduced by impact is used to introduce compressive residual stress and work hardening to target material surfaces [33]. It was reported that femtosecond laser peening improved fatigue strength of FSWed 7075-T73 aluminum alloys [41] With these three types of laser peening, laser ablation impact is used; these are a kind of shotless peening, as shot is not used. It has been reported that the fatigue strength of stainless steel treated by cavitation peening is better than that of shot peening, water jet peening, and submerged laser peening [43,50]. To clarify the effect of residual stress on the fatigue properties of FSWed AA5754, surface residual stress was measured with a 2D method using X-ray diffraction
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