The characterization of the A1-12 Wt Pct Si flake powder produced by a double-disk process

A double-disk (DD) process was developed in this study for producing highly elongated flakes which are very promising for application as a filler for conductive composites with a plastic matrix. The Al-12Si alloy was selected as the experimental alloy in view of its high stiffness, strength, and integrity which are beneficial for retaining its high aspect ratio during the fabrication of the composites. Various operational parameters,i.e., pouring temperature and the rotational speeds of upper disk and quenching disk, were monitored in the powder production to reveal their effects on the size distribution and morphology of flakes. The flake formation mechanism was also investigated. Experimental results indicate that the broad size distribution of the flakes produced by the double-disk process rises from the splat-quenching effect and the formation of interlinked flakes and whisker-shaped flakes. The mean particle size (or mean flake width) increases with a decreasing rotational speed of centrifugal disk or quenching disk speed, but is little influenced by pouring temperature. The length-to-width ratio of flakes varies with the rotational speed of quenching disk but inversely with pouring temperature, centrifugal disk speed, and flake width. The thickness varies inversely with all of these variables. The aspect ratio varies with pouring temperature, rotational speed of quenching disk, and flake width, but varies inversely with centrifugal disk speed. All of these variations might be accounted for by considering the solidification rate and dragging rate. Based on these two rates, theoretical relationships for length-to-width ratio, thickness, and aspect ratio as a function of various metallurgical factors are derived and correlate sufficiently with the trends of experimental data.