Microstructure evolution of spray-formed hypereutectic Al-Si alloys in semisolid reheating process
(School of Materials Science and Engineering, Central South University, Changsha 410083, China)
Abstract: The Al-27%Si alloy was prepared by the spray forming process, and its microstructure evolution during the semisolid reheating process was investigated. The results show that, the primary Si phase coarsens during the reheating process and the coarsening rate increases with the increase of reheating temperature. The eutectic phase is produced in the molten region when quenched in the cold water. The microstructure evolution in the semisolid state can be divided into three stages. The remarkable characteristic of the first stage is only a solid-state phase transformation process. However, the region around the α(Al) matrix gradually melts in the second stage. The primary Si in the liquid phase coarsens obviously, and the eutectic phase is produced in the molten region when the specimens are quenched in cold water. In the last stage, the same thing as that in the second stage happens except that all the α(Al) matrixes are melted.
Key words: spray forming; Al-Si alloy; semisolid; coarsening rate