Variation du module d'young associee a la precipitation de la phase θ′ dans un alliage AlCu 4%

Abstract

Change in Young's modulus during the precipitation of the θ phase has been studied in the alloy aluminium-4 wt.% Copper. The microstructural evolution has been followed by election microscopy. The experimental results show that θ′ precipitation is accompanied by a 3 per cent increase of Young's modulus. This increase is independent of the precipitate size; it depends essentially on the precipitated volume fraction and on the coherency state of the precipitate-matrix interface. Three main factors explain the evolution of Young's modulus E during the precipitation of θ′: —impoverishment in copper of the solid solution —inclusion effect of the θ′ precipitate (increase of E) —loss of coherency on the large faces of the θ′-precipitates (decrease of E). The change in modulus associated with the decrease in copper concentration of the matrix depends on the temperature T m at which the module has been measured. At low temperature ( T m < −100 degrees centigrade), the impoverishment of the matrix in copper has a negligible effect and the increase in alloy modulus is due only to the inclusion effect. For T < − 100° C, the decreasing copper concentration of the matrix induces an increase of the modulus of this matrix, the more important as T m is higher: This indicates that Young's modulus of the AI-4 per cent Cu solid solution decreases more rapidly than that of Al. when temperature increases.