Abstract
Aging characterisics of the weld metal in the commercial Al-Zn-Mg alloy were studied by means of hardeness measurements and X-ray small angle scattering methods. Isothermal aging curves of hardness, particle size and integrated intensity were obtained at room temperature, 80°C and 135°C. From these aging curves, the aging process of the weld metal in the commercial Al-Zn-Mg alloy was discussed. Changes in hardness were in good correspondence with those in particle size and integrated intensity. It was found that hardness distribution in the weld matal was uniform at any aging temperature and aging time, which corresponded to macroscopically uniform distribution of solute atoms in the weld metal. It was also shown that hardness was always lower in the weld metal than in the heat-affected zone during aging at any temperature. This was due to micro-segregation of Zn atoms in the weld metal. Aging processes of specimens, solution-treated after welding, water-quenched, and aged at 80°C and 135°C, were compared with those directly aged at the same temperatures after welding. It was found that the aging process at 135°C depended on the above heat treatments after welding while the aging occurred in a similar way at 80°C. This results was discussed in terms of thermal histories of specimens before aging.
