Surface quality evaluation of hot deformed aluminum
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Surface quality evaluation of hot deformed aluminum L.A. Espinosa Zúñiga* 1, F.A. Pérez González 1, O. Zapata 1, N.F. Garza Montes de Oca 1, S. Haro 2 1
Facultad de Ingeniería Mecánica y Eléctrica, Universidad Autónoma de Nuevo León, UANL, AP-149F, CP-66451, Cd. Universitaria, N.L. México. 2 Unidad Académica de Ingeniería, Universidad Autónoma de Zacatecas, Av. López Velarde No. 801, Centro, C.P. 98000, Zacatecas, Zac. México.
ABSTRACT The surface quality of a heat treatable Al-Si-Mg alloy by means compression tests at 450°C was evaluated. Samples were obtained from an ingot with unidirectional solidification in order to obtain a microstructural gradient influenced by the cooling and solidification rate. The samples were heat treated by homogenization at 520°C for 4 hours prior to deformation by compression. Inverted optical and scanning electron microscopes were used to assess the surface damage of deformed samples. Analysis of deformed surface indicates a greater influence of microstructural refinement on hardening rate. It was found that the samples solidified at high cooling rates showed no defects, but at low cooling rates produced growth of grain size and intermetallic phases and thereby the high incidence of cracks in the surface.
INTRODUCTION The Al–Si systems are most commonly used as aluminum foundry alloys over a wide range of mechanical and thermal applications where strength at elevated temperature is important. The type of the 6XXX series alloys are based on aluminum-magnesium-silicon system (Al-Mg-Si) and are widely used for manufacturing profiles by extrusion [1]. Among the characteristics of the series 6XXX alloy is the formation of particles (Mg2Si) which is beneficial for the material as it can be heat treated and modify the mechanical properties of the material. The formation of intermetallic particles Al-Fe-Si during solidification at preferential locations such as grain boundaries and interdendritic regions; these particles have a non-circular or laminar morphology, in the grinding plane, and can cause cracks [2-4]. Common manufacturing process of aluminum ingots for extrusion is a semi-continuous casting, followed by cooling of the material, where different solidification rates are obtained from 1 K/s in the center to about 20 K/s on the surface, makes the rate of solidification is a variable to consideration because this variation promotes microstructural differences [5-6]. The formability of the material depends of the chemical composition and homogeneity formed during solidification [7].
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Figure 1. Schematic ingot casting showing localization of samples. Another important aspect is the surface quality after extrusion process, since due to mechanical deformation the material may exhibit surface cracks, which could be due to different factors, such as the chemistr
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