2001 Volume 19 Issue 1 Pages 114-121
YAG laser welding was performed on A5052-O and -H34 sheets (thickness: 2 mm) in several different welding speeds with the constant out put power of 2000 W. The authors investigated the distribution of Vickers hardness in both weld metal and heat-affected zone (HAZ), and the influence of heat treatment on Vickers hardness in the weld metal from the view point of micro segregation of magnesium in dendrites.
In the HAZ of A5052-H34, the soft region where the hardness is almost the same as A5052-O base metal is developed just near the fusion boundary. Then the hardness increases with the increase in the distance from the fusion boundary toward the base metal and finally reaches the value equal to A5052-H34 base metal. This is caused by the change of the maximum temperatures in the HAZ due to welding.
In the weld metal of both A5052-O and -H34 the hardness increases and dendrite arm spacing decreases as welding speed increases. When the heat treatment is performed on the weld metal at 500°C for 24 h, the hardness decreases down to the value of A5052-O base metal. According to the simulation on the diffusion of magnesium in aluminum during the heat treatment, the micro segregation in dendrites tends to decrease with the increase in both the heat temperature and the holding time. This phenomenon was confirmed by EPMA analysis. These results lead to the conclusion that the higher hardness in the weld metal than that of A5052-O base metal is caused by the micro segregation of magnesium in dendrites.
