Influence of fluidized sand bed heat treatment on the performance of Al–Si cast alloys Kh.A. Ragab a , A.M. Samuel a , A.M.A. Al-Ahmari b , F.H. Samuel a,b,⇑ , H.W. Doty c a Université du Québec à Chicoutimi, Chicoutimi, Quebec, Canada G7H 2B1 b Center of Excellence for Research in Engineering Materials, College of Engineering, King Saud University, Riyadh, Saudi Arabia c GM Powertrain Group, Metal Casting Technology, Milford, NH 03055, USA article info Article history: Received 26 May 2010 Accepted 21 October 2010 Available online 27 October 2010 Keywords: A. Non-ferrous metals and alloys C. Heat treatments E. Mechanical abstract The present study was undertaken to arrive at a better understanding of the effects of solution heat-treat- ment time and melt treatment on the microstructure and tensile properties of T6-tempered A356.2 and B319.2 cast alloys heat treated using a fluidized sand bed furnace (FB) as opposed to a conventional con- vection furnace (CF). The alloys investigated were subjected to solution heat treatment at 530 °C and 495 °C, respectively, for times ranging from 0.5 to 24 h, warm water quenching, and conventional T6 aging at 155 °C and 180 °C, respectively, for times of 0.5, 1, 5, 8 and 12 h. The results revealed that the tensile strength of these alloys is more responsive to an FB heat treatment than to a CF treatment for solu- tion treatment times of up to 8 h. A significant increase in strength is observed in the FB heat-treated samples after short aging times of 0.5 h and 1 h, the trend continuing up to 5 h. Analysis of the tensile properties in terms of quality index charts showed that both modified and non-modified 319 and 356 alloys display the same quality, or better, after only 2 h treatment in a fluidized bed compared to 10 h using a CF treatment. The 319 alloys show signs of overaging after 8 h of aging using a CF, whereas with an FB, overaging occurs only after 12 h. The Si particle characteristics of the alloys investigated show that the smallest particle size is obtained after solution heat treatment using a fluidized sand bed, the opti- mum solution heat-treatment time being 0.5 h for modified alloys, and up to 5 h for non-modified alloys. Ó 2010 Elsevier Ltd. All rights reserved. 1. Introduction The increasing demand for weight reduction and low fuel con- sumption in the automotive industry has had a marked effect on the judicious selection of materials. The high strength-to-weight ratio, high fluidity, low thermal expansion coefficient, and high corrosion resistance of Al–Si cast alloys, typically B319.2 and A356.2, make them materials of choice for the automotive industry especially when it concerns engine construction [1–3]. Traditional heat treatment technology applies circulating air convection furnaces for solution heat treating and aging for the purposes of obtaining a T6 or T7 temper. In this study, the T6 heat treatment was used to increase the strength of a cast part through precipitation hardening. The T6 temper involves a sequence which includes solution heat treatment, rapid cooling in water, and arti- ficial aging. With conventional heat treating systems, however, prolonged solutionizing times – over 20 h – are required for heat treatment entailing high energy costs [4–6]. The fluidized sand bed heat-treating process makes it possible to reduce the time re- quired for heat treating significantly, while at the same time increasing the uniformity of the heat treatment process [7,8]. The fluidized sand bed supplies an excellent heat transfer of 120–1200 W/m 2 °C, which is higher than the 80–90 W/m 2 °C at- tained by conventional furnaces [9–12]. The global heat transfer coefficient of a fluidized sand bed is related to the temperature of the heat-treated part in the bed through the following heat transfer and energy balance equations: Q ðtÞ¼ hAðT FB  T p ðtÞÞ ¼ mc p dTp=dt ð1Þ T p ðtÞ¼ T FB þðT p ð0Þ T FB Þ expðhAt=mc p Þ ð2Þ where Q(t) is the heat flow rate, h is the heat transfer coefficient, A is the surface area of the part, T p (t) is the part temperature as a func- tion of time, T FB is the bulk fluidized bed temperature, m is the mass of the part, C p is the specific heat of the part, and T p (0) is the initial temperature of the part [13–15]. With regard to solution heat treating, it has long been held in the industry that several hours are required for adequate treat- ment using a convection furnace. Samuel et al. [16,17] reported that the best solution heat-treatment time for high Mg-containing 319 alloys at 500 °C is 8–10 h using a convection furnace. Also, due 0261-3069/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.matdes.2010.10.023 ⇑ Corresponding author at: Address: Département des Sciences Appliquées, Université du Québec à Chicoutimi, 555, Boulevard de l’Université, Chicoutimi, Québec, Canada G7H 2B1. Tel.: +1 418 545 5406 (Office); fax: +1 418 545 5012. E-mail address: fhsamuel@uqac.ca (F.H. Samuel). Materials and Design 32 (2011) 1177–1193 Contents lists available at ScienceDirect Materials and Design journal homepage: www.elsevier.com/locate/matdes