Ic. Stone et H. Jones, EFFECT OF COOLING RATE AND FRONT VELOCITY ON SOLIDIFICATION MICROSTRUCTURE SELECTION IN AL-3.5WT-PERCENT-FE-O TO 8.5WT-PERCENT-SI ALLOYS, Materials science & engineering. A, Structural materials: properties, microstructure and processing, 226, 1997, pp. 33-37
The aim of this work was to study the effect of solidification conditi
ons on microstructure selection in Al-3.5Fe-0 to 8.5Si (wt. %) alloys
cooled under non-equilibrium conditions. The alloys studied were Al-3.
5Fe, Al-3.5Fe-1Si, Al-3.5Fe-2.8Si, Al-3.5Fe-7Si and Al-3.5Fe-8.5Si (wt
. %), which were solidified by wedge chill casting and Bridgman direct
ional solidification. Wedge casting gave cooling rates in the range 10
(0)-10(3) K s(-1), whilst Bridgman solidification was carried out at f
ront velocities between 10(-2) and 2 mm s(-1), and a temperature gradi
ent of about 15 K mm(-1). Far the first three alloy compositions, the
first phase to appear for the slower cooled regimes was the equilibriu
m primary phase of Al13Fe4. Material which solidified in wedge casting
s at cooling rates greater than about 150 K s(-1) did so without forma
tion of primary intermetallic and had microstructures of alpha-Al dend
rites with interdendritic eutectic. Primary intermetallic was also sup
pressed in the Bridgman solidified material al front velocities greate
r than approximately 1 mm s(-1). The as-solidified microstructure of t
he ahoy containing 8.5 wt.% Si at lower cooling rates in the wedge and
at all front velocities in Bridgman solidified material contained pri
mary beta-AlFeSi intermetallic in preference to the expected alpha-typ
e AlFeSi ternary intermetallic, suggesting a shift in the liquidus sur
face phase boundaries. (C) 1997 Elsevier Science S.A.