THE CHARACTERIZATION OF THE AL-12 WT PCT SI FLAKE POWDER PRODUCED BY A DOUBLE-DISK PROCESS

A double-disk (DD) process was developed in this study for producing h ighly elongated flakes which are very promising for application as a f iller for conductive composites with a plastic matrix. The Al-12Si all oy was selected as the experimental alloy in view of its high stiffnes s, strength, and integrity which are beneficial for retaining its high aspect ratio during the fabrication of the composites. Various operat ional parameters, i.e., pouring temperature and the rotational speeds of upper disk and quenching disk, were monitored in the powder product ion to reveal their effects on the size distribution and morphology of flakes. The flake formation mechanism was also investigated. Experime ntal results indicate that the broad size distribution of the flakes p roduced by the double-disk process rises from the splat-quenching effe ct and the formation of interlinked flakes and whisker-shaped flakes. The mean particle size (or mean flake width) increases with a decreasi ng rotational speed of centrifugal disk or quenching disk speed, but i s little influenced by pouring temperature. The length-to-width ratio of flakes varies with the rotational speed of quenching disk but inver sely with pouring temperature, centrifugal disk speed, and flake width . The thickness varies inversely with all of these variables. The aspe ct ratio varies with pouring temperature, rotational speed of quenchin g disk, and flake width, but varies inversely with centrifugal disk sp eed. All of these variations might be accounted for by considering the solidification rate and dragging rate. Based on these two rates, theo retical 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.