| Specific heat versus temperature curves been obtained by the Nagasaki-Takagi method on polycrystalline specimens of Al-rich Al-Ag. Al-Cu, Al-Zn, Al-Zn-Mg, Al-Cu-Mg and Al-Mg-Si alloys, during reheating after various age-hardening treatments. The results have been analysed in comparison with those of the hardness tests, dilatometric, X-ray structural and electrical resistivity measurements and electron microscopic observations. The thermal analysis is useful proving further information on the low temperature ageing or the first stage of the ageing, its relation to the high temperature ageing formation of the G.P. zones and metastable phases. The reversion phenomena in the alloys aged at low temperatures are attributed to the d;ssolution of the G.P. zones. The effects of the ageing temperature and ageing time upon both the reversion temperature and the heat of reversion have been examined from the heat absorption, and it has been confirmed that the reversion temperature rises with ageing temperature. |
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