Influence of Pressure and Temperature on Microstructure and Mechanical Behavior of Squeeze Cast Mg-10Gd-3Y-0.5Zr Alloy
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TRODUCTION
RECENT research reports of Mg alloys containing heavy rare earth elements (REs) suggest that it is possible to attain combinations of mechanical properties that are attractive for the automotive and aerospace industries.[1–5] Among the various alloys studied, the Mg-Gd-Y and its derivative Mg-10Gd-3Y-0.5Zr (GW103K) show mechanical properties and creep resistance that are superior to those of the more established, commercial series WE (Mg-Y-Nd-Zr), WE43, and WE54[6] alloys. It is also evident, however, that commonly used conventional casting processes, such as permanent casting, are not ideally suited to manufacture Mg-RE alloys, partly due to the low production efficiency and secondary machining that are typically required by these approaches. Although high-pressure die casting (HPDC) has been proposed as an alternative approach to address production efficiency, HPDC castings cannot be solution treated at elevated CUNLONG WANG, Ph.D. Candidate, is with the National Engineering Research Center of Light Alloys Net Forming, Shanghai Jiao Tong University, Shanghai 200240, P. R. China, and also with the Department of Chemical Engineering and Materials Science, University of California, Irvine, CA 92697. ENRIQUE J. LAVERNIA, Professor, is with the Department of Chemical Engineering and Materials Science, University of California. GUOHUA WU and WENJIANG DING, Professors, and WENCAI LIU, Assistant Researcher, are with the National Engineering Research Center of Light Alloys Net Forming, Shanghai Jiao Tong University. Contact e-mail: [email protected] Manuscript submitted February 10, 2016. Article published online May 13, 2016 4104—VOLUME 47A, AUGUST 2016
temperatures due to the gas entrapment that occurs during die filling,[7–9] which inherently limits the ability to induce precipitation hardening. Furthermore, approaches such as permanent casting and HPDC fail to eliminate common casting defects, such as shrinkage, porosity, and solute segregation.[8] In contrast to the more established casting techniques described above, squeeze casting combines casting and forging into a single step by applying pressure during solidification of the alloys. The superimposed pressure limits gas entrapment during die filling, thereby allowing for subsequent solution treatment of the alloys. Moreover, the application of an external pressure during solidification provides several advantages, including (1) enhancing the cooling rate by increasing the heat transfer rate between the alloy melt and the mold wall; (2) eliminating casting porosity, shrinkage, and reducing the tendency for hot tearing during solidification; and (3) limiting the development of macroscopic solute segregation by restricting atomic movement.[10,11] In the past decade, squeeze casting has been applied to a variety of Al alloys and Al-based metal matrix composites.[12–16] More recently, however, studies involving squeeze casting of Mg alloys have been published. For example, Masoumi and Hu[17] reported that when a squeeze casting pressure of 90 MPa is used, nearly poro
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