*Article* **Improving Fatigue Performance of Laser-Welded 2024-T3 Aluminum Alloy Using Dry Laser Peening**

### **Tomokazu Sano 1,\*, Takayuki Eimura 1, Akio Hirose 1, Yosuke Kawahito 2, Seiji Katayama 2, Kazuto Arakawa 3, Kiyotaka Masaki 4, Ayumi Shiro 5, Takahisa Shobu 6 and Yuji Sano 7,8**


Received: 23 September 2019; Accepted: 4 November 2019; Published: 6 November 2019

**Abstract:** The purpose of the present study was to verify the effectiveness of dry laser peening (DryLP), which is the peening technique without a sacrificial overlay under atmospheric conditions using femtosecond laser pulses on the mechanical properties such as hardness, residual stress, and fatigue performance of laser-welded 2024 aluminum alloy containing welding defects such as undercuts and blowholes. After DryLP treatment of the laser-welded 2024 aluminum alloy, the softened weld metal recovered to the original hardness of base metal, while residual tensile stress in the weld metal and heat-affected zone changed to compressive stresses. As a result, DryLP treatment improved the fatigue performances of welded specimens with and without the weld reinforcement almost equally. The fatigue life almost doubled at a stress amplitude of 180 MPa and increased by a factor of more than 50 at 120 MPa. DryLP was found to be more effective for improving the fatigue performance of laser-welded aluminum specimens with welding defects at lower stress amplitudes, as stress concentration at the defects did not significantly influence the fatigue performance.

**Keywords:** dry laser peening; femtosecond laser; shock wave; laser welding; 2024 aluminum alloy
