PARTICULATE INCORPORATION PROCESS AND UNIFORMITY OF PARTICULATE DISTRIBUTION OF THE ALUMINUM MATRIX COMPOSITE MANUFACTURED BY MELT STIRRING METHOD

The process of particulate incorporation into liquid aluminum and the uniformity of particulate distribution in the matrix were investigated. During the melt-stirring period, particles take three different states as follows: (a) as powders, (b) particulate agglomerates combined with metal, and (c) particles incorporated in the matrix. During the early stage of stirring, particulate incorporation does not start, although agglomerates are formed. However, particulate incorporation begins rapidly after a definite time of stirring (tau). Comparing the incorporation process of SiC particles with the wetting process of SiC plate to liquid aluminum, the wettability is found to be a dominant factor for the particulate incorporation process. The particulate distribution was not uniform just after particulate incorporation has finished, because particles were incorporated into melt at agglomerates. However, a sufficient stirring time makes the uniformity of particulate dispersion better. On the other hand, by adding surface active elements such as Pb or Bi, which decreases the surface energy of liquid aluminum, the uniformity of particulate dispersion in Al-Li and Al-Mg liquid aluminum alloys was improved in a shorter stirring time.