Dry Laser Peening: Improving Fatigue Properties of Friction Stir-Welded/Laser-Welded 2024 Aluminum AlloysTuesday (23.06.2020) 10:10 - 10:50 Room 2
Fatigue properties of friction stir-welded/laser-welded 2024 aluminum alloys are improved using dry laser peening (DryLP) method, which is newly developed for realizing completely dry process without a sacrificial overlay such as a plasma confinement medium in air using femtosecond laser pulses [1-4]. The intensity of a femtosecond laser pulse is extremely high even at a low energy because the pulse width is extremely short. Therefore, direct irradiation of a solid surface with a femtosecond laser pulse drives an intense shock wave that propagates into the solid. Such a shock wave driven by the femtosecond laser pulse irradiated under atmospheric conditions deforms a material plastically [5-8]. Heat-affected and melted zones formed by a femtosecond laser pulse are much smaller than those produced by a nanosecond laser pulse due to its extremely short pulse width. Therefore, such a DryLP without a sacrificial overlay under atmospheric conditions is proposed to be possible using a femtosecond laser pulse. However, effects of the DryLP on mechanical properties of laser-welded joints has never been reported. Changes of hardness, residual stress and fatigue properties of friction stir-welded/laser-welded 2024 aluminum alloys between before and after the DryLP were investigated in this study. As a result of plane bending fatigue test of the laser-welded joints (Figs. 1 and 2), the fatigue life of the DryLPed specimen was improved as much as 15 times in comparison with the as-welded specimen at stress amplitude of 120 MPa. This DryLP is found to be effective to other kinds of aluminum alloys such as 6061 and 7075 aluminum alloys, therefore this process has a potential to be applied to variety of industrial fields such as automotive, rail, aircraft, and space industries.
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