EFFECT OF TERNARY ADDITIONS ON THE AGEING CHARACTERISTICS OF SOME ALUMINIUM.-ZINC ALLOYS

Abstract

The influence of homogenisation temperature, ageing temperature and solute concentration on the rate of pre-precipitation has been studied employing resis — tivity and hardness measurements. Whereas hardness mea-surement was restricted only to binary Al-Zn alloys, resistivity measurements were extended to two ternary additions of In also. It has been found that both resistivity and hardness increase with ageing time and that the hardness curves are characterized by a well-defined incubation period while resistivity starts increasing almost instanta-neously. Time taken to reach the resistivity maxima and "flat hardness are strongly dependent of the homogenisa-tion and ageing temperatures. Homogenisation temperature is found to have no influence on the resistivity peak and "flat hardness" while these are strongly dependent on the ageing temperature. It is observed that addition of In to the binary alloys lowers the rate of pre-precipitation and higher the In content, slower is the ageing