Influence of dendrite arm spacing on the thermal conductivity of an aluminum-silicon casting alloy
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Influence of dendrite arm spacing on the thermal conductivity of an aluminum-silicon casting alloy C. Va´zquez-Lo´pez Departamento de Fı´sica, Centro de Investigaci´on y de Estudios Avanzados del IPN, A. P. 14-740, Me´xico, 07000, D.F., Mexico
A. Caldero´n and M.E. Rodrı´guez Centro de Investigacio´n en Ciencia Aplicada y Tecnologia Avanzada del IPN, Calzada Legaria No. 694, Col. Irrigacio´n, Me´xico 11500, D.F. Mexico
E. Velasco and S. Cano Corporativo Nemak, S. A. de C. V., A. P. A-100, Monterrey, 66000, N.L. Mexico
R. Cola´s Facultad de Ingenierı´a Meca´nica y Ele´ctrica, Universidad Auto´noma de Nuevo Leo´n, A. P. 149-F, Cd. Universitaria, San Nicola´s de los Garza, 66451, N.L. Mexico
S. Valtierra Corporativo Nemak, S. A. de C. V., A. P. A-100, Monterrey, 66000, N.L. Mexico (Received 27 May 1999; accepted 7 October 1999)
The photoacoustic technique and the thermal relaxation method were used to determine the thermal conductivity of some representative samples obtained from an aluminumsilicon casting alloy A319. This material was solidified with an imposed unidirectional thermal gradient to obtain samples with different microstructures characterized by the secondary dendrite arm spacing, which increases as the solidification rate decreases. It was found that the thermal conductivity of the alloy decreases with an increase in the secondary dendrite arm spacing and a decrease in the integral dendrite perimeter.
I. INTRODUCTION
The importance of simple thermal diffusivity measurements is crucial in the use of several industrial alloys, in particular those which are subjected to thermal cycling, such as aluminum alloys employed in the manufacture of automotive engines, since power dissipation is an important mechanism in engine performance.1 The microstructure which is developed in a casting depends on its solidification rate.2,3 In the case of the widely used hypoeutectic aluminum silicon alloys, the typical microstructure is composed of aluminum dendrites and a dispersion of the eutectic when made from aluminum and nearly pure silicon.2,3 The secondary dendrite arm spacing (DAS) was found to be reduced as the solidification rate increased,3,4 whereas the shape and distribution of eutectic silicon is affected by a series of parameters such as solidification rate and chemical composition.5–7 It is a well-known fact that the physical and mechanical properties of a material depend on its microstructure,5,6,8,9 but the relationship between the thermophysical properties and microstructure is perhaps less studied, although some reports9,10 indicate that the electrical conductivity depends on the microstructure. J. Mater. Res., Vol. 15, No. 1, Jan 2000
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The experimental methods commonly employed to determine the thermal diffusivity in materials are of three different types, depending on whether the measured heat flow is stationary, (conventional method11) transient or periodic. The American Society for Testing Mater
