On the Reversion of Al-rich Al-Zn and Al-Ag Alloys

Abstract

The changes of electrical resistance and small angle scattering of X-ray for Al-Zn alloys aged at various temperatures were compared with those for Al-Ag alloys in order to know the behaviour of zones during the reversion treatment. Results obtained are as follows: (1) Small angle scattering of CuKα radiation from Al-30 wt% Zn alloys annealed at temperatures higher than 94°C show the existence of zones at these temperatures. (2) A maximum of electrical resistance in the isothermal aging curves is obtained at 130°C or 140°C for an Al-10 wt% Zn alloy. Therefore, zones are known to be formed at these temperatures. (3) At temperatures higher than 94°C, electrical resistance of specimens of an Al-10 wt% Zn alloy decreases with the increase of temperature, and increases again when the temperature is lowered. These results support the existence of the zones mentioned above. (4) Electrical resistance of the aged Al-Zn alloy specimens decreases by reversion treatment to the values which are obtained by annealing the as-quenched specimens for the same period at the same temperature as the reversion treatment. (5) Electrical resistance of Al-Ag alloys aged for a long time at a low temperature increases by reversion treatment to the values which are obtained by annealing the as-quenched specimens for the same period at the same temperature as the reversion treatment, but these values are much lower than as-quenched one. (6) On reaging, electrical resistance of the Al-Zn alloy specimens increases slowly, but that of Al-Ag alloys decreases.