| The influences of addition of Fe, Si, Mn and Ti on the age-precipitation in Al-2.6wt%Cu-0.4wt%Mg alloy have been investigated by means of the measurement of electric resistivity, specific heat and transmission electron microscopy. Internal energy changes for the G.P.B. zones, S` and S precipitates occurred during ageing, have been determined from the specific heat versus temperature curves. The results have been analysed in comparision with those from measurement of electrical resistivity and electron microscopy. The results obtained are summarized as follows. 1) The rate of G.P.B. zone formation is accelerated slightly by the addition of Mn and pronouncedly by the addition of Ti. 2) The rate of G.P.B. zone formation is retarded pronouncedly by the addition of Si and Fe. From these results, it can be deduced out that the additions of Si and Fe increase the sinks of quenched-in vacancy such as the grain boundary and dislocation, and decrease the effective vacancy concentration contributing to the formation of G.P.B. zones. 3) The precipitation of metastable S` phase is retarded by the addition of Fe and Si, However, the precipitation of metastable S` phase is more retarded by the addition of Si than Fe, and the precipitation of equilibrium S phase is by the addition of Fe than Si. |
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