Hot compression and industrial extrusion characteristics of an as-cast Al-10Sr master alloy

Abstract The mechanical properties and castability of Al-Si-based alloys can be remarkably improved by adding Al-Sr master alloy, which modifies the structure and morphology of eutectic silicon. The size of Al4Sr phases in Al-Sr master alloy has been found to take key effect in Sr-modification. To obtain optimized processing parameters and understand the refinement mechanisms of Al4Sr phases during plastic deformation, the hot compression and industrial extrusion characteristics of an as-cast Al-10Sr master alloy were systematically investigated in this work. The results showed that the flow behavior of the Al-10Sr master alloy can be well described by a constitutive equation with the hot deformation activation energy of 222.23 kJ/mol. The obtained optimum processing region was located at temperature of 460–530 °C and strain rate of 0.2–1 s−1 from the established processing maps. During hot compression testing, plastic deformation mainly occurred in soft Al matrix and the Al4Sr phases were slightly broken. During industrial extrusion process, the Al4Sr phases were refined effectively based on the above optimum processing conditions. Comparing to conventional extrusion process, repetitive Conform process showed better ability in refining Al4Sr phases. After three repetitive Conform passes, the length of Al4Sr phases decreased from 80 to 11 μm and the width decreased from 25.6 to 8.3 μm, and the Al4Sr phases were also distributed homogeneously. The in-depth refinement mechanisms of Al4Sr phases during plastic forming were also discussed based on microstructural examinations and finite element analysis.