Effect of Solidification Rate and Heat Treating on the Microstructure and Tensile Behavior of an Aluminum-Copper Alloy
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THE automotive industry relies on the use of cast aluminum alloys to manufacture pieces with limited structural demands and to obtain weight savings by replacing iron castings; typical examples are cylinder heads and engine blocks. Recent advances in manufacturing and casting processes have made it possible to obtain aluminum castings that exhibit an excellent combination of weight reduction and mechanical properties; an example of these are struts and other components incorporated into the direction and suspension systems.[1,2] These pieces have to be reliable and sustain the demands imposed by constant beating and fatigue, which are achieved by reducing the incidence of surface and internal defects. The parameter that exerts the highest influence on the levels of strength and internal quality demanded by
M.A. TALAMANTES-SILVA, formerly Undergraduate Student, Facultad de Ingenierı´ a Meca´nica y Ele´ctrica, Universidad Auto´noma de Nuevo Leo´n, is Graduate Student, Department of Engineering Materials, University of Sheffield, S1 3JD Sheffield, Great Britain. R. COLA´S, Professor, is with the Facultad de Ingenierı´ a Meca´nica y Ele´ctrica, Universidad Auto´noma de Nuevo Leo´n, A.P. 149-F, 66451 San Nicola´s de los Garza, N.L., Mexico. Contact e-mail: rcolas@mail. uanl.mx A. RODRI´GUEZ and J. TALAMANTES-SILVA are with Nemak, S.A. de C.V., Libramiento Arco Vial km 3.8, 66221 Garcı´ a, N.L., Mexico. S. VALTIERRA, Director for Innovation, is with Owens Corning, Privada la Puerta 1110-A, Parque Industrial La Puerta, 66350 Santa Catarina, N.L., Mexico. Manuscript submitted May 19, 2008. Article published online November 7, 2008. METALLURGICAL AND MATERIALS TRANSACTIONS B
structural parts is the solidification rate. The microstructure of the material is refined when solidification proceeds at a faster rate. The main parameters that are affected are the spacing between the secondary arms of dendrites, which depends on the heat-transfer rate. The grain size and the spacing and size of eutectic aggregates are reduced due to enhanced nucleation and reduction in the growth rate. Porosity due to contraction will be more finely dispersed and the pores will be reduced in size.[3–6] A further advantage of microstructural refining when dealing with aluminum alloys susceptible for heat treating is the enhancement in their mechanical properties, because the particles formed during solidification will be smaller and will require less time to dissolve at the treating temperature, reducing with it the deleterious effects due to coarsening.[5,6] Most commercial automotive castings are based on the 3XX series, because silicon imparts good fluidity and the addition of either magnesium or copper allows for enhancing their strength by heat treating.[3–9] The continuous demand for higher mechanical properties makes 3XX alloys unsuitable for certain uses. Such properties can be fulfilled by Al-Cu alloys, but these alloys exhibit low fluidity and are more difficult to cast than silicon bearing alloys.[7–9] The aim of this work is to present the results of t
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