Control of liquid segregation of semi-solid aluminum alloys during intelligent compression test

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Abstract
Thixoforming is becoming increasingly popular for manufacturing near-net shape parts and has so many advantages compared with conventional forming technologies that it has spread and been studied worldwide. Components produced by semi-solid forming process have good mechanical properties and less defects such as porosity. A relationship between stress and stain is very important to design a die to avoid defects of products during semi-solid forming process. Since the liquid will be of eutectic composition in alloys, liquid segregation will result in significant or undesirable situations. The materials used in this experiment are A357, A390, Al2024 alloys that have been fabricated by the electromagnetic stirring process. In the compression test with the semi-solid state materials the liquid phase coexists with globularized solid particles. Billet temperature corresponding to the desired solid fraction is controlled by an induction heating system. The intelligent compression test was performed by induction heating and MTS. During compression, specimen temperatures were continuously measured. The liquid segregation is controlled by changes in the strain rate and solid fraction during the compression process. The characteristics of flow between solid and liquid phase considering liquid segregation is examined. Generally, it is known that if the applied stress to semi-solid alloys is below the yield stress, the alloys show solid-like behavior but, if the applied stress exceeds the yield stress, the semi-solid alloys flow like liquid. Therefore, it is important to establish the yield point to predict the rheological behavior of semi-solid alloys.