Aluminum-silicon-magnesium (Al-Si-Mg) alloys, due to their excellent castability and high strength-to-weight ratio, are the most widely used aluminum foundry alloys. This alloy is extensively used in aerospace and automotive industries. The cast microstructure of these alloys consists of a primary phase, aluminum or silicon and a eutectic mixture of these two microcomponents.
In addition, the mechanical properties of these alloys are mainly dictated by the characteristics of eutectic microcomponents in the microstructure. Furthermore, many investigations have been conducted on the semi-solid macrostructures to control the matrix (Al-alpha) and eutectic phase (silicon) morphologies.
As the thermomechanical treatment (TMT) is one of the most effective materials processing techniques, the objective of this research was to study the influence of TMT parameters on Si morphology in aluminum 356 alloys with two semisolid and conventional casting macrostructures. Therefore, hot compression tests have been carried out in a range of temperature (420°C to 540°C) and strain rate (0.1, 0.01, and 0.001 sec-1). The results indicated that the morphology of Si phase was changed from acicular to spherical shape and:
1. The observed dynamic flow softening was mainly related to silicon platelets fragmentation and spheroidization.
2. The faults driving force approach was adapted to explain the silicon platelets fragmentation and spheroidization under deformation at high temperatures.
3. Maximum UTS and El for alloy in 540oC, 0.1 sec-1 and 540oC, 0.001 sec-1 respectively.
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