Microstructure and mechanical properties of Al-Mg2Si composite fabricated in-situ by vibrating cooling slope

An innovative semisolid technique termed as vibrating cooling slope (VCS) has been applied to producing in-situ Al-25%Mg2Si (mass fraction) composite. The molten Al-16.5Mg-9.4%Si (mass fraction) alloy with 100 °C superheat was poured on the surface of an inclined copper plate (set at 45° inclined angle) while it was vibrated at a frequency of 40 Hz and an amplitude of 400 μm. After travelling the length of 40 cm on the slope, the resultant semisolid alloy was cast into a steel mold. For the purpose of comparison, reference composite samples were made by gravity casting (GC) and conventionally still cooling slope casting (CS) methods using the same alloy under identical conditions. The samples were hot extruded at 500 °C. It was concluded that the size of Mg2Si particles was decreased by about 50% and 70% for the CS and VCS produced samples respectively when compared to that of the GC produced sample. Despite of their higher porosity contents, both the as-cast and hot-extruded VCS processed samples exhibited higher hardness, shear yield stress (SYS) and ultimate shear strength (USS) values as compared with their GC produced counterparts. These results were attributed to the refined and modified microstructure obtained via this newly developed technique.