The Strength of the Spatially Interconnected Eutectic Network in HPDC Mg-La, Mg-Nd, and Mg-La-Nd Alloys
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THE volume fraction of eutectic in high pressure die cast (HPDC) Mg alloys may be as high as 30 pct, and a number of workers[1–7] have suggested that because of the profuse spatial interconnection it should account for a measurable fraction of the casting’s strength in excess of the contribution stemming from dispersion hardening. Recent focused ion beam (FIB) sectioning and reconstruction work on cast-to-shape tensile specimens[3,8] of HPDC AZ91D alloy showed that the spatial interconnection of the percolating b-Mg17Al12 eutectic involved as much as 95 pct of the intermetallic near the casting surface, or skin region, dropping to about 50 pct at the center of the cross section, or casting core.
BAO ZHANG, Research Associate, formerly with ARC Centre of Excellence for Design in Light Metals, Materials Engineering, School of Engineering, The University of Queensland, Brisbane, QLD 4072, Australia, is now with Imperial College, London, U.K. SERGE GAVRAS, Postgraduate Student, is with the CAST Co-operative Research Centre, Department of Materials Engineering, Monash University, Monash, VIC 3800, Australia. ANUMALASETTY V. NAGASEKHAR, Research Metallurgist, formerly with ARC Centre of Excellence for Design in Light Metals, Materials Engineering, School of Engineering, The University of Queensland, is now with Carpenter Technology Corporation, PO Box 14662, Reading, PA. CARLOS HORACIO CA´CERES, Reader, is with ARC Centre of Excellence for Design in Light Metals, Materials Engineering, School of Engineering, The University of Queensland. Contact e-mail: [email protected] MARK A. EASTON, Professor, formerely with CAST Co-operative Research Centre, Department of Materials Engineering, Monash University, also with Royal Melbourne Institute of Technology, Melbourne, VIC, Australia, is now with School of Aerospace, Mechanical and Manufacturing Engineering, RMIT University, Carlton, VIC 3053, Australia. Manuscript submitted November 27, 2013. METALLURGICAL AND MATERIALS TRANSACTIONS A
Numerical modeling of the deformation behavior of the eutectic network showed that it adds ~7 MPa to the specimens’ strength,[9] or about 5 pct of its total strength exclusively through the spatial interconnection. Similar modeling for a Mg-Ce alloy showed that the strengthening stemming from the 3D network may be as high as 25 MPa, or about 17 pct of the total strength.[10] The present study extends the authors’ prior modelling work on AZ91 and Mg-Ce alloys[9,10] to two binary MgRE alloys, Mg-0.62 at. pctLa, and a Mg-0.60 at. pctNd. FIB tomography was used to determine the 3D morphological features of the percolating networks, and finite element modelling (FEM) via ABAQUS codes was used to characterize their deformation behavior and estimate their concomitant strengthening effects. The results of the modelling were subsequently validated using two ternary Mg-La-Nd alloys of a parallel study.[11] The two binary alloys used for the FEM modelling were from the same batches studied in Reference 7. The two alloys were deliberately chosen wit
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