EBSD and DTA Characterization of A356 Alloy Deformed by ECAP During Reheating and Partial Re-melting
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RODUCTION
THIXOFORMING is a semi-solid metal processing route (SSM) in which the forming of alloys is carried out in the semi-solid state to manufacture near net-shaped products.[1,2] To make this feasible, the microstructure of the semi-solid must be non-dendritic. According to numerous research and industrial experiments, the thixocasting process improves component integrity and performance.[3–5] Until recently, many techniques have been developed to obtain semi-solid non-dendritic microstructures via solid or liquid routes. Solid state techniques, such as strain-induced melt activated (SIMA) and recrystallization and partial re-melting (RAP) processes, consist of plastic deformation below or above the recrystallization temperature, followed by partial re-melting in which the liquid phase nucleates in MARZYEH MORADI, Graduate Student, is with the School of Metallurgy and Materials Engineering, University of Tehran, Tehran, Iran, and also with Mechanical Engineering and Materials, Swanson School of Engineering, University of Pittsburgh, Pittsburgh, PA. MAHMOUD NILI-AHMADABADI, Professor, is with the School of Metallurgy and Materials Engineering, University of Tehran, and also with the Center of Excellence for High Performance Material, University of Tehran, Tehran, Iran. Contact e-mail: [email protected] BEHRANG POORGANJI, Research Scientist, is with the University of Cincinnati, OH, and also with the Institute for Materials Research, Tohoku University, Sendai, Japan. BASHIR HEIDARIAN, Graduate Student, is with the School of Metallurgy and Materials Engineering, University of Tehran. TADASHI FURUHARA, Professor, is with the Institute for Materials Research, Microstructure Design of Structural Metallic Materials, Tohoku University, Sendai, Japan. Manuscript submitted May 18, 2010. Article published online November 7, 2013 1540—VOLUME 45A, MARCH 2014
high angle grain boundaries (HAGBs) of recrystallized grains leading to the detachment of grains.[6–8] In the SIMA and RAP processes, the accumulated strain energy provides the nucleation sites for recrystallization and promotes the transformation of deformed dendritic microstructures into equiaxed microstructures.[9,10] When the temperature reaches above the solidus, high-energy grain boundaries of new recrystallized grains are penetrated by liquid, leading to the detachment of grains.[7,10,11] The size of the recrystallized grains during the reheating process determines the particle size in the semi-solid state. The finer and the more globular-shape particles in the semi-solid slurries are the major factors for the success of semi-solid forming processes. In addition, in the reheating process, the heating rate also plays an important role in determining the size of solid particles in semi-solid slurries. Hence, an understanding of the recrystallization process with respect to the strain level and heating rate is useful to achieve finer particle sizes. Until now, many studies have been carried out to investigate the microstructural evolution of different alloys through parti
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