[en] Aluminum alloys have often been used as the material for structural components of research and test reactors. However the data on the strength characteristics of these alloys have been not obtained enough to evaluate the structural integrity of research reactor components. Thus, the material tests for evaluating the strength in the base metal and welded joint of A5052 and A6061 alloys were performed at JAERI. Mechanical Engineering Division has cooperated in the fabrication of the welded plate to be used in the above tests. Technical examination has been carried out to satisfy the 1 ^st grade requirement of the radiographic examination method by JIS-Z3105. A major problem in the welding of above aluminum alloys is to reduce the blow hole and crack. Especially it is difficult to avoid such welding defects in A6061 alloy. In the fabrication of the welded plates, optimized welding condition to obtain good welding joints was established. This report describes the improvements in the welding techniques to reduce defects base GTAW (Gas- Tungsten Arc Welding) process. (author)