Journal of Mechanical Science and Technology 28 (10) (2014) 4267~4274 www.springerlink.com/content/1738-494x DOI 10.1007/s12206-014-0940-6 Investigation of the controlled atmosphere of semisolid metal processing of A356 aluminium alloy † A. Kolahdooz, S. Nourouzi * , M. Bakhshi and S. J. Hosseinipour Department of Mechanical Engineering, Babol University of Technology, Babol, 47148-71167, Iran (Manuscript Received February 5, 2014; Revised May 10, 2014; Accepted June 10, 2014) ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- Abstract The cooling slope (CS) method is one of the semi-solid methods in which the molten alloy with a suitable amount of superheat is poured on a cooling slope to achieve a fine and non-dendritic structure. After pouring, the melt, which becomes semisolid at the end of the plate, is subsequently poured into a cylindrical steel mold with different mold temperatures. Also, the process has been done in differ- ent cooling slopes and different cooling lengths. This work, at first discusses the effect of these parameters on the final microstructure of A356 aluminum alloy and then the effect of the controlled atmosphere is discussed. Also, in this research, the advantages of using the controlled atmosphere system are discussed by tests such as XRD, SEM and ultrasonic test. Results indicate that the pouring temperature, mold temperature, cooling slope and cooling length have significant effects on the size and morphology of α-Al phase. Also, the con- trolled atmosphere could optimize the process as well and increase the mechanical properties of alloy. Keywords: Semisolid; Casting; Solidification; A356 Al-Alloy; Argon gas ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- 1. Introduction Since the beginning of 1970s, the semi-solid forming tech- nology has been developing rapidly, and it is known as the forefront of metal processing technology [1, 2]. Different from the conventional metal forming technologies which use either solid metals (solid state processing) or liquid metals (casting) as starting materials, SSM processing deals with semisolid slurries [3]. In semi-solid processes, shear rate is applied to a molten metal which is in its solidifying range, and dendrite micro-structure is broken and changed to globular micro- structure [4]. A number of mechanisms have been put forward by various researchers to explain the transformation of dendrites to spher- oidal morphology. Vogel [5] believed that in the presence of shear rate, dendrites bend and break to lower the surface of their energy. The second theory is presented by Hellawel [6]. He believed that breaking dendrites is the result of local re- melting of dendrites in root. Mullis et al. [7] assumed that the solute convection, due to stirring, caused the transformation of dendrites to spheroidal morphology. Many methods have been introduced for the production of semisolid slurries since it is scientifically sound and industrially viable with such preferred microstructures called thixotropic microstructures as feedstock materials [8]. Among all the techniques of semi-solid metal processes, the cooling slope (CS) process is a simple route, which can develop non-dendritic slurry for cited purposes with reduced equipment and processing costs. It uses an inclined plate that is cooled underneath. The mol- ten alloy with low superheat is poured on the plate and solidi- fied with globular microstructure while rolling down the plate and cooling simultaneously [9-11]. In the CS method, various parameters can affect the final microstructure. Many investi- gations have been performed in order to produce such refiner and more globular microstructure as a feedstock using this method. Haga [12] performed semisolid strip casting, a type of rheo- casting, by use of a melt drag twin roll caster equipped with a cooling slope. Difficulty of analyzing the cooling slope process due to its multiplicity of effective parameters and their interactions with each other proves the importance of the process simulation. Kund et al. [13] simulated the cooling slope semisolid casting of A356 alloy. At their work the influence of inlet velocity, pouring temperature, slope angle, and slope length on tem- perature distribution, velocity distribution and macro- segregation was investigated. Wang et al. [14] by simulating the cooling slope process, investigated the influence of inlet temperature and velocity, the cooling slope temperature and the mold temperature on the ingot's temperature, solid fraction, solid particles distribution * Corresponding author. Tel.: +98 911 325 3509, Fax.: +98 111 3212268 E-mail address: s-nourouzi@nit.ac.ir † Recommended by Editor Sung-Lim Ko © KSME & Springer 2014