N. K. Gobran

Effect of cold work on the dissolution kinetics in the precipitating Al-2 wt% Mg alloy

The fracture stress σf was taken to assess the mechanism of dissolution of the Β-phase in the Al-2 wt% Mg alloy. The role of pre-cold working the polycrystalline samples was investigated. The dissolution of the Β-phase was carried out at different temperatures. The relation between the fracture stress and the time of dissolution showed peaky curves. The rise of σf towards a maximum was attributed to the progressive dissolution of the precipitates. The position of the peak was found to shift towards lower times of dissolution with the increase of the dissolution temperature or the increase of the pre-cold work. Considering the peak position indicative of a certain degree of dissolution, equivalent times and temperatures of the dissolution mechanism were thus found and the activation energy was calculated. Pre-cold working the samples before the dissolution act decreased the activation energy responsible for the process from 1·95×10−19 J to about 0·48× 10−19 J. The initial drop in σf observed for heavily cold worked samples pointed towards the possible effect of excess vacancies created by cold work.