On enhancing the interfacial chemistry of a simulated AA2014-SiCp composite material

The use of aluminum alloys in automotive applications has increased significantly in recent years due to the need for more fuel-efficient vehicles. These alloys alone do not enjoy the strength offered by traditional ferrous products. However, the development of new alloys through micro/macroalloying and the incorporation of load-bearing materials such as SiC into the matrix have enhanced their popularity. Unfortunately metal matrix composites such as AA2014-SiC often fail catastrophically due to fibre or particulate pullout in service. Such failures are difficult to predict and are often a result of poor wetting at the metal/reinforcement interface. In the present work Sn and Ni were examined as potential sintering/wetting aids. In particular, Sn or Ni (0.5–2 w%) were added to a simulated AA2014 alloy (Al-4Cu-0.5Mg) with and without 14.5 w% SiC following standard powder metallurgy techniques. Because the distribution of blend constituents is of critical importance various dispersants were evaluated. Best particle dispersion was obtained using oleic acid while mixing for 8 h. Sintering temperatures ranged from 605–620°C and both green and final densities were determined using mercury densitometry. Resulting microstructures were examined using scanning electron microscopy and electron probe microanalysis with particular attention directed to the SiC-alloy interface. Nickel was found to enhance the wetting of SiC by AA2014 and the interfacial region was found to be chemically superior to a commercial copper-coated SiC product. Tin contributed to an increase in intermetallic formation. It is believed that the improved interfacial region was due to the presence of a small amount of liquid phase at the AA2014-SiC interface giving a chemical rather than the usual mechanical bond between reinforcement and alloy.