Investigation of the controlled atmosphere of semisolid metal processing of A356 aluminium alloy
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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 different 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 controlled 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 technology 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 microstructure [4]. A number of mechanisms have been put forward by various researchers to explain the transformation of dendrites to spheroidal 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 remelting of dendrites in root. Mullis et al. [7] as
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