Abstract
Following the previous study that showed the occurrence of the abrupt change in the low temperature aging phenomena in Al-Zn-Mg alloys by a small amount of Mg which affected the number of phases, the present study was conducted to see the similar change in the high temperature aging in Al-5at%Zn-Mg alloys. After solution treatment at 470°C, specimens were quenched into iced water and aged at 100°C and 150°C. Aging was followed by hardness, electrical resistivity and calorimetric measurement and transmission electron microscopy. As in the low temperature aging, the marked difference in the aging phenomena between the two and three phase alloys was found to exist; the two phase alloy did not develop age hardening and showed no maximum in resistivitytime curves, while the three phase alloy developed age hardening and showed a maximum in a resistivity curve.
