Welding processes in various industries such as shipbuilding, railroads, aircraft, and construction are inevitably accompanied by HAZ(Heat Affected Zone) deformation and metal structure changes around the toe of the welding bead. It is widely known that it is very weak in terms of structural strength because the tensile residual stress is introduced by welding, and the surface is also rough, causing the main cause of stress concentration to occur. It also becomes the damage initiation cite to the welded structure. Post-welding heat treatment, grinder, and TIG dressing methods were used to release residual stress and to eliminate defects in the welding part. Recently, various peening technologies using pulsed heat sources of laser, elastic vibration energy of ultrasonic waves, compressed air or cavitation have been developed and are being actively utilized as performance improvement and standardized safety technologies in the field. The local peening process on the surface of the welded part and the welded heat-affected part is not only easily portable by various technical methods, but is also being applied to robots or hybrid-3D printing technology. Therefore, in this technical paper, the technical analysis of the various advanced peening technologies that are currently being utilized and the device development trend are evaluated. The portable ultrasonic peening equipment was developed and the recently applied technologies that are newly grafted to improve mechanical properties are introduced.

In order to commercialize the Fe-Al joining technology using arc heat source, it is necessary to guarantee about static and dynamic strength. However, no studies have been conducted to evaluate the fatigue strength of Al-Fe joints using arc heat sources. Therefore, ultrasonic fatigue test to the overlap joint structure of dissimilar materials was examined at first. For the ultrasonic elastic resonance experiment, the plate type specimen of the overlap joint was designed based on the design theory of the ultrasonic fatigue specimen. As a result, it was confirmed that the ultrasonic fatigue test for the overlap joint was sufficiently applicable through the thermal imaging camera measurement. Also the result of ultrasonic fatigue test according to the heat input and the presence of gap, the fatigue life depend on increasing heat input was reduced due to inverse proportion to the growth of the root pore. On the other hand, if the gap is present, fatigue life is improved up to 25% as much as the static strength by removing a considerable amount of pores. When compared to other studies on the fatigue of aluminum lap joints, this fatigue limit is sufficiently competitive if a method to control the pores is constructed.