Abstract
5083 aluminum alloy plate of 10 mm thickness was welded by MIG pulse arc process. Then, impact test was performed on base and weld metal at room temperature, -75 and -196°C. For the weld metal, Charpy impact test was also performed on the weld metal after homogenization at 500°C for 20 hours.
Mg content dissolved in the weld metal was approximately the same near the fusion boundary as near the center of the weld metal and was 2.87 and 2.80%, respectively. On the other hand, the Mg content dissolved in the base metal was 4.45%. When the homogenizing was performed on the weld metal at 500°C for 2 hours, the dissolved Mg content increased to 4.10% and the content did not change after longer homogenized time.
Charpy impact values were approximately the same at -196°C as at the room temperature for the base metal. For the weld metal, however, the values at -196°C were lower than those at room tem-perature. This phenomenon was mainly due to the decrease of crack propagation energy. After the homogenization of the weld metal the Charpy impact values increased. Besides, crack initiation energy increased approximately linearly when the dissolved Mg content increased.
On the fracture surface of the weld metal dimple patterns were observed at room temperature and quasi-cleavage like structure was mainly observed at -196°C. After the homogenization of the weld metal, the dimple patterns were observed on considerably wider area of the fracture surface even at -196°C
