Microstructure and impact behavior of Al/SiCp composites fabricated by pressureless infiltration with different types of SiCp

The effect of the type of SiCp (green or black), Mg content in the aluminum alloy and holding time on the microstructure and impact strength of Al/SiCp composites fabricated by pressureless infiltration was investigated. Preforms of SiCp in the form of rectangular bars (10cmX1cmX1cm) were infiltrated at 1150 deg C in argon- > nitrogen atmosphere for 45 and 60min utilizing two aluminum alloys (Al-6Mg-11Si and Al-9Mg-11Si) (wt.%). Results show that the presence of a higher amount of black SiC has a beneficial effect in the composites microstructure because it prevents formation of the unwanted Al4C3 phase. The impact strength is enhanced when the Mg content varies from 6 to 9 wt.% and decreases when the Al4C3 phase is present. Moreover, a higher amount of Mg in the alloy is reflected in a lower residual porosity and consequently in a higher impact strength in the composites.