Improvement of the Liquid Segregation Phenomena of Semisolid Aluminum Alloys by the Multistage Strain Rate Control in the Compression Test

Abstract

The deformation behavior of semisolid aluminum alloys in the range of solid fraction (fs) between 55 and 90% was investigated through compression tests for the variation of strain rate. In order to obtain the optimal conditions of the net shape forging process, the rheological behavior of aluminum alloy in the semisolid state has been examined by using parallel plate compression. The strain rate is the value of the strain rate corresponding to the stress to avoid the liquid segregation phenomena during compression tests. The material constants of semisolid material in the stress-strain curve are proposed to perform the numerical analysis for a die design of semisolid forging. The starting materials used in this experiment are A357, 86S (similar to A319), and A390 alloys, which are fabricated by the electromagnetic stirring process. The intelligent compression test with a controlled strain rate was performed. The liquid segregation in the overall cross-sectional areas is controlled as the multistage variation of the pressing velocity and variation of the solid fraction during the compression process. The characteristics of materials flow between solid and liquid phases, considering the liquid segregation, are discussed for various solid fractions and pressing velocities.