Calorimetric Study of Precipitation in a Commercial (7075) Aluminum Alloy.
GRUMMAN AEROSPACE CORP BETHPAGE N Y RESEARCH DEPT
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Specific heat, hardness, and transmission electron microscopy were used to evaluate the solid state reactions related to solution and aging heat treatments and their effect on mechanical strengthening. Calorimetric studies indicate three endothermic and two exothermic reactions on heating from 25C to 470C. The endotherms are due to reversion of GP zones P sub 1, dissolution of intermediate MgZn2 type precipitate, eta, P sub 3, and dissolution of the stable MgZn2 type precipitate, eta, P sub 5 exotherms P sub 2, and P sub 4 accompany precipitation of the eta and eta, respectively. Energies associated with P sub 1 and P sub 2 P sub 4 increased with solution treatment temperature and time, while that P sub 5 decreased. Hardness also increased with higher heat input during solution treatment and was found to be a function of GP zone concentration. The results suggest that maximum strength is based on the partition of excess solute between internal surface defects and GP zones. Precipitation at these defects depletes matrix solute and reduces attainable strength. Author
- Properties of Metals and Alloys