Influence of melt superheating on microstructure evolution in Al-Mg2Si composites fabricated by gravity casting and vibrating cooling slope methods

Al-based composites, reinforced with Mg2Si particulates have been recently considered as a new group of metal matrix composites that offer attractive properties such as low density and good wear resistance. However, coarse Mg2Si particulates with a sharp edged morphology may deteriorate the mechanical properties of these composites. In the present study, an innovative semisolid technique termed as Vibrating Cooling Slope (VCS) has been applied to produce in-situ Al-25wt.%Mg2Si composites. An inclined plate that could vibrate mechanically in the vertical direction at a predetermined frequency was used as the cooling slope. The molten Al-16.5%Mg-9.4%Si alloy with 100, 200 or 300 C superheating temperatures was poured on the surface of this cooling slope while it was vibrating at the frequency of 60 Hz and amplitude of 680μm. The melt travelled the distance of 400 mm before being poured into a cylindrical cast-iron mould. Also for the purpose of comparison, gravity casting was carried out using the same mould. The samples were sectioned, polished and subjected to metallographic studies. The results revealed that in comparison with the gravity casting, the VCS processed samples exhibited considerably finer primary Mg2Si particulates. Moreover, with increasing of melt superheating temperature, the size of the primary Mg2Si particles decreased and increased for gravity casting and VCS samples respectively

Keywords:

Al-Mg2Si composite , Vibrating cooling slope , Superheating temperature , Microstructure