VOL. 11, NO. 10, MAY 2016 ISSN 1819-6608 ARPN Journal of Engineering and Applied Sciences © 2006-2016 Asian Research Publishing Network (ARPN). All rights reserved. www.arpnjournals.com 6502 EFFECT OF THICKNESS ON MICROSTRUCTURE AND POROSITY OF AL-SI ALLOY IN VORTEX GATING SYSTEM R. Ahmad and M. B. A. Asmael Department of Manufacturing and Industrial Engineering, Faculty of Mechanical and Manufacturing Engineering, Universiti Tun Hussein Onn Malaysia, Parit Raja, Batu Pahat, Johor, Malaysia E-Mail: roslee@uthm.edu.my ABSTRACT The effect of thickness of vortex gating system on microstructure, velocity and porosity of A314 cast alloy was investigated. Three different thicknesses of 20, 25 and 30 mm were simulated and casted. The data of simulation showed the thicker gating reduced the velocity of the melt. In addition, increased thickness in vortex gate contributes to better eutectic interlaminar spacing. The best quality of casting (less porosity) was obtained with large thickness of vortex gating system. Keywords: vortex gating system, aluminium alloy, microstructure. INTRODUCTION Casting is a manufacturing process by which a liquid material is usually poured into a mold, which contains a hollow cavity of the desired shape, and then allowed to solidify. The solidified part is also known as a casting, which is ejected or broken out of the mold to complete the process. Casting materials are usually metals or various cold setting materials, that cure after mixing two or more components together such as epoxy, concrete, plaster and clay (Maheswari and Sureshkumar 2013). Casting is the most often used for making complex shapes, that would otherwise be difficult or uneconomical to make by other methods. Out of all the casting processes created throughout, sand casting stands out in the crowd as being one of the oldest methods of metal casting processes. This is mainly due to its capability of producing moderate to complex parts with low cost consumption. At first, castings produced using sand casting usually exposed to countless defects caused by whether the sand being swept along by the molten metal flow inside the cavity, slow cooling rate of the sand or even low surface finish of the parts. However, that was a thing of the past as sand casting has evolved (Ammen 1979). The vortex has usually been regarded in foundries as a flow feature to be avoided at all cost and this is because the vortex generally swallowed air, and the air found its way into the molten metal, the vortex flow certainly have to be avoided. Designers of water intakes for hydroelectric power stations are well aware of this benefit. Instead of the water being allowed to tumble haphazardly down the water intake from the reservoir, it caused to spiral down the walls. At the base of the intake duct, the loss of rotational energy allows the duct to back- fill to some extent. The central core of air terminates at the level surface of a comparatively tranquil pool, only gently circulating, near the base of the duct (Campbell 2004). Vortex gate is a novel design applied in sand casting to deal with the central issue of high liquid velocity running through the runners. Otherwise, high velocity flow that enters the mould will have the tendency to damage the metal. It is considered to be highly effective in reducing the generation of inclusion by surface turbulence at the gate (Dai, Yang et al. 2003). In addition, Vortex gate are also designed to absorb energy from the melt flowing through the runners or in other words, it will act like a ceramic foam filter. In vortex gate design, there are not many parameters that had been developed or investigated in order to provide better understanding of the design (Kasala, Pernis et al.). Aluminum alloys have been the primary materials for structural components of military aircrafts, helicopters, amphibians, etc for several decades. This may attribute to the low density of aluminium in mass critical application. The Al-Si aluminium alloys have been widely used in the automotive industry due to its good casting characteristics and mechanical properties (Asmael, Ahmad et al. 2014). Producing defect-free Al castings becomes more important (Ahmad, Asmael et al. 2014). The most important factors for all casting processes are feasibility, cost factors and quality factors. Quality factors are also important in the selection of a casting process. When applied to castings, the term quality refers to both degree of soundness (freedom from porosity, cracking and surface imperfections) and levels of mechanical properties (strength and ductility). In terms of feasibility, many aluminium alloy castings can be produced by any of the available methods (Ahmad, Talib et al. 2013). As reported, the vortex gating system shows an increment of mechanical strength of Aluminium LM25 alloy casting and lower porosity content than conventional gating system (Subhy 2010). For the vortex well design, porosity inside the casting was significantly reduced, while the mechanical strength and reliability of the aluminium casting were further enhanced (Ahmad and Talib 2011). Furthermore, the velocity of the metal fluid flowing through the runner often faces problem of being too high. In most cases the velocity tends to exceed its critical velocity, which offers percentage of inclusions occuring in the melt. Although vortex gate is known to