Effects of Electro-Magnetic Stirring on Microstructural Evolution and Mechanical Properties in Semi-Solid Forming of a Hypo-Eutectic Al-Si-Cu-Ni-Mg Alloy

摘要

A new piston alloy based on a hypo-eutectic Al-Si-Cu-Ni-Mg system was developed for semi-solid forming. The Si content was optimized to obtain proper semi-solid slurry based on thermodynamic calculations and experiments. The contents of Cu, Ni and Mg were kept similar to those of a commercial piston alloy to retain good heat resistance and high-strength properties. The high-quality semi-solid slurry with fine and uniform globular characteristics for semi-solid forming can be obtained at a low pouring temperature of 615°C. The conditions of a T6 heat treatment for the developed alloy are optimized as follows: solid solution treatment at 520°C for 6 h and an aging treatment at 160°C for 5 h. The mechanical properties, in this case hardness, high-temperature tensile strength, relative wear resistance, and high-temperature creep, were evaluated by the specimens which were taken from the rheo-diecast products and the results were compared with those of a conventional metal mold cast piston.