The Room and Elevated Temperature Tensile Properties of a Unidirectionally Solidified Quasi-Binary Al–S (Cu2Mg2Al5) Eutectic Composite Alloy

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Abstract
The room and elevated temperature tensile properties of a unidirectionally solidified quasi-binary Al–S(Cu2Mg2Al5) eutectic composite alloy have been studied. In the case of the slowly solidified specimens, in which almost all the S lamellae were oriented parallel to the solidification direction, the deformation behavior was in good agreement with that predicted by a modified rule of mixtures. In the rapidly solidified specimens, the colony structure and local coarsening of the S phase were found to occur and the fracture strength of these specimens decreased. The Young’s moduli EcI and EcII had a tendency to decrease slightly with an increase of the solidification rate. The measured (Remark: Graphics omitted.) had larger values than those predicted by the rule of mixtures. The fracture strength increased by the aging treatment, due to the increase in both the fracture strain and the fraction of the S lamellae longer than the critical length. At room temperature, the fracture of the specimens was controlled mainly by the propagation of cracks in the S lamellae. On the contrary, at elevated temperatures above 200°C, the S lamellae showed neckings due to an increase in plasticity. The influence of the solidification rate on the fracture strength at room temperature was presented in a simple formula, based mainly on the crack propagation in the S phase.