EFFECT OF PRESSURE ON PRECIPITATION IN AN AL-4.3PERCENT CU ALLOY

The effect of hydrostatic pressures up to 12 kbar on the rates of formation of θ” and θ' precipitates in an Al-4·3% Cu alloy has been studied. Pressure strongly inhibits the rates of formation of these precipitates. The θ” precipitates were formed at 170θc and the θ' at 220°c. The activation volume for the θ” formation was 12·4±0·4 cm3 mole−1 and that for θ' formation was 12·3±0·6 cm3 mole−1, i.e. effectively the same. Measurements of rates of formation of θ” and θ' at various temperatures at atmospheric pressure also give the same activation energy of 27·45 kcal mole−1 (1·19 ev) for the formation of the two types of precipitate. © 1969 Taylor & Francis Group, LLC.