THE EFFECT OF TEMPERATURE-GRADIENT AND GROWTH-RATE ON SPACING BETWEEN PRIMARY SILICON PARTICLES IN RAPIDLY SOLIDIFIED HYPEREUTECTIC ALUMINUM SILICON ALLOYS

Measurements of the number of N0 of primary silicon particles per unit area in hypereutectic Al-Si alloys subjected to front velocity controlled rapid solidification by TIG weld traversing, Bridgman growth and laser surface melt traversing are shown to conform to the single relationship N0(GV1/2)1/2 = 4.1 +/- 0.8 s1/2 mm-3/2 K-1, equivalent to lambda(GV1/2)1/2 = 87 +/- 11-mu-m3/4 K1/2 s-1/4, where lambda is the mean spacing N0-1/2 between particles. This result is in parametric agreement with the Hunt and Kurz-Fisher model predictions and the magnitude of lambda(GV1/2)1/2 is midway between their respective predictions, as found previously for succinonitrile-acetone and Al-2 wt% Cu.