An Enhanced Steady-State Constitutive Model for Semi-solid Forming of Al7075 Based on Cross Model
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RODUCTION
MODELING of the behavior of the semi-solid metal is a crucial issue in thixoforming processes.[1] This process is a near-net-shape forming method for metals and alloys. It is very suitable for the economic production of complex components and structures with superior mechanical properties. The semi-solid forming process occurs in the temperature range between the solidus and the liquidus. The process includes three stages: (1) preparation of spherical microstructure, (2) heating to a semi-solid temperature and holding for a determined time, and (3) final forming.[2] To study the rheological behavior of semi-solid alloys, many globularization routes have been suggested. Campo et al.[3] evaluated the influence of five different processing routes on the production of the thixotropic aluminum alloy. They showed that the prepared samples by the stress-induced melt-activated (SIMA) route have the most appropriate microstructural characteristics, including smaller grain sizes and greater shape factors for semi-solid forming. In their study, the pre-strain inducing process of the SIMA route was the equal channel angular pressing (ECAP). This method is one of
RAMIN MESHKABADI is with the Department of Mechanical Engineering, Ahar Branch, Islamic Azad University, Ahar, Iran. VAHID POUYAFAR and AKBAR JAVDANI are with the Department of Mechanical Engineering, University of Tabriz, Tabriz, 5166616471, Iran. GHADER FARAJI is with the School of Mechanical Engineering, College of Engineering, University of Tehran, Tehran, 11155-4563, Iran. Contact e-mail: [email protected] Manuscript submitted February 12, 2017.
METALLURGICAL AND MATERIALS TRANSACTIONS A
the best methods of applying a large homogeneous strain and unlike forging and extrusion methods, the cross-section of the sample does not change.[4,5] In another research, Campo et al.[6] investigated the microstructure evolution and thixotropic behavior of the ECAP-treated material in the semi-solid state. They concluded that the ECAP-treated sample exhibits a high thixoformability and produces a suitable raw material for semi-solid forming. Based on the great potential of ECAP-treated materials for semi-solid forming, a proper knowledge of the material flow is necessary for numerical simulation, and it assures the successful completion of the forming process. Since the semi-solid forming process takes place in a short time, it is impossible to study the flow properties by experimental methods.[7] The use of simulation techniques and constitutive equations can be useful to this end. Application of constitutive equations for predicting the flow behavior of semi-solid alloys has been developed in recent years, and so that they can be used for optimizing the process parameters and theoretical studying of the process.[8,9] Several constitutive equations have been developed to describe the flow behavior of semi-solid alloys. The most widely used models are the Power law (Eq. [1]) and Bingham plastic (Eq. [2]) with each of them having two adjustable parameters. The Power law model
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