Constellation, le dépôt institutionnel de l'Université du Québec à Chicoutimi

Résumé

This study explored the effects of compositional variation of Al-Cu 206 alloys (Si and Mn concentrations, 0.12 versus 0.3 wt.% each) on the precipitation and thermal stability of h¢ precipitates, and the associated elevated-temperature strengths during long-term thermal exposure at 300 C. The results indicated that both alloys under the T7 condition exhibited comparable yield strengths at 20 and 300 C, which were predominantly controlled by h¢ precipitates. Upon exposure at 300 C for up to 1000 h, the h¢ precipitates in the alloy with low Si and Mn concentrations remained stable and resistant to transformation into the equilibrium h phase. The coarsening of h¢ proceeded through both lengthening and thickening, resulting in the continuing decline in YS at 300 C from 93 MPa after 300 C/100 h to 78 MPa after 300 C/1000 h. Conversely, the h¢ precipitates in the alloy with high Si and Mn concentrations underwent almost complete transformation into deleterious h after only 100 h at 300 C, thus imparting a significantly lower YS of 69 MPa after 300 C/100 h. The possible sources of these microstructure and property changes with the compositional variation were explored. This study has implications for strategic design of Al-Cu alloys for high-temperature applications.