Influence of Solute Addition in the Microstructure and Hardness of the Al-Si-Cu Alloys
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Influence of Solute Addition in the Microstructure and Hardness of the Al-Si-Cu Alloys H. M. Medrano-Prieto1, C.G. Garay-Reyes1, C.D. Gómez-Esparza1 and R. Martínez-Sánchez1 1 Dirección. Centro de Investigación en Materiales Avanzados (CIMAV), Laboratorio Nacional de Nanotecnología, Miguel de Cervantes No. 120, C.P. 31136, Chihuahua, Chih., México ABSTRACT Commercial aluminum alloys corresponding to Al-Cu-Si family are commonly used in casting and molding process because their high castability. The main characteristics of these alloys are the excellent weight/strength relation in conjunction with wear and corrosion resistance. Additionally, the mechanical properties of these alloys could be enhanced by heat treatment. In Al A319 alloys, Cu and Mg are the main responsible to increase the mechanical properties after T6 heat treatment due to the precipitation of Al2Cu and Mg2Si and Al2CuMg phase [1]. Combined effects of Ni and Cu improve strength and hardness at relatively elevated temperature [2], Due to the low solubility of Ni in Al (0.04%), it has been reported the formation of FeAl9FeNi-type intermetallic, which is not totally dissolved with the typical solution treatments used in aluminum alloys [3]. Hayajneh et al., found that increasing amounts of intermetallic compounds Al3Ni, Al3(CuNi)2 and Al7Cu4Ni in Al-Cu alloy, the hardness increase [4]. The effect of Ni addition and solution treatment time on the microstructure and hardness of the Al A319 alloy are studied by Vickers microhardness (VHN), Rockwell B hardness (HRB), X Ray Diffraction (XRD), Optical Microscopy (OM), Scanning Electron Microscopy (SEM). INTRODUCTION The A319 Al alloy belonging to the Al-Si alloy system is commonly used in the automotive industry, due to its excellent combination of strength and ductility [6], moreover, of its high strength/weight ratio, corrosion resistance and excellent thermal conductivity [5]. Additionally, its high cast ability allows the casting of complex forms. This alloy is generally heat treated to obtain optimum mechanical properties [5]. The effects of heat treatments have been studied by different techniques and authors [6, 7, 5, 8, 9, 1], where the following results highlight, the β-Mg2Si and θ-Al2Cu phases are dissolved during the solubilized treatment, but were not dissolved Fe-rich phases as, Al8Mg3FeSi6 and αAl15(Fe,Mn)3Si2, only the β-Al5FeSi phase is fragmented and gradually dissolved at high temperatures [5]. Through of addition of small amounts (~0.01%) of Na, Sr, Ca, or Sb during the solubilized treatment, were observed eutectic Si morphological changes since acicular to fibers or globules (spheroidization) [10, 7].The increase in the mechanical properties of hardness and mechanical strength is obtained by precipitating the θ-Al2Cu phase during aging [5]. In Al alloys, the Ni, Fe, Ce and other transition metals, which, the main characteristic is their low solubility in Al (maximum of 0.01% to 0.03%), are employed to reduce the coefficient of thermal expansion [10]. The Al-Ni intermetallic compounds have
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