The effect of growth velocity and temperature gradient on growth characteristics of matrix eutectic in a hypereutectic aluminium-silicon alloy

Abstract

The growth undercooling ΔT and eutectic interlamellar spacing λ, have been measured as functions of growth velocityV and temperature gradientG for matrix Al-Si eutectic in the presence of primary silicon in Bridgman-grown hypereutectic Al-18.3 wt% Si alloy. ΔT/V ^1/2 shows a step decrease atV>270 μm s⁻¹ corresponding to a change in eutectic growth morphology from flake-like to fibrous, but there was no corresponding change in λV ^1/2. Analysis of published data on the effect ofG on λV ^1/2 for the Al-Si eutectic shows good agreement with the single relationship λV ^1/2=A G ⁻ⁿwithA=56±8 μm^3/2 s^−1/2(K mm⁻¹)ⁿ andn=0.24±0.03 for the range 0.1<V<6×10⁴ μm s⁻¹ and 0.7<G<2000 K mm⁻¹.