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

Résumé

The semisolid tensile properties of two AA6111 direct-chill cast alloys (A and B) have been studied. The Cu, Mn, and Si contents of alloy A are higher than those of alloy B. The microstructures of the alloys were analyzed before tensile testing and after tensile fracture. Isothermal holding was performed in the temperatures of 510, 520, 535, 552, 564 and 580 °C for 1 h to study porosity/void formation in both alloys. Tensile tests were conducted near the solidus temperature in the temperature range of 450–580 °C at a strain rate of 10–4 s−1. The strain during tensile testing was measured using the digital image correlation method to obtain reliable stress–strain curves. The results revealed that the tensile strengths of the alloys gradually decreased to zero with increasing temperature to arrive at the zero-stress temperature, whereas the strains at the failure decreased sharply with increasing temperature until zero-ductility temperature (ZDT) was reached. Moreover, the failure strain of alloy B at any given testing temperature was higher than that of alloy A. Non-mechanical and mechanical hot-tearing criteria were used to study the hot-tearing susceptibilities (HTSs) of the alloys. Considering the mechanical criterion, the ZDT and brittle temperature range of alloy A were lower and larger than those of alloy B, respectively, indicating that the HTS index of alloy A was higher than that of alloy B.