The Influence of Al Content and Thickness on the Microstructure and Tensile Properties in High-Pressure Die Cast Magnesi
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DUE to their high specific strength and good castability, magnesium alloys are desirable for use in weight reduction strategies for automotive applications.[1,2] Over 95 pct of magnesium parts for structural applications are manufactured using the high-pressure die casting process.[3,4] High-pressure die casting (HPDC) allows large, thin-walled components to be mass-produced rapidly and economically. In HPDC, highly turbulent molten metal flows into the shaped die cavity, generating a broad distribution of microstructures through the thickness and in different regions of a single casting.[5,6] The heterogeneity observed in the microstructure of cast components leads to increased variability in the observed tensile properties as shown by Forsmark et al.[7] The use of magnesium alloy die castings is limited partially by the variability in mechanical properties observed in HPDC components.[8] This variability necessitates conservatively designed HPDC parts and limits the ability to use HPDC components in crash-sensitive applications where ductility and deformation behavior are especially important. It is commonly believed that these properties, particularly the ductility, strongly depend on porosity levels.[9–11] For this reason, super vacuum die casting (SVDC) technology is being explored to minimize the presence of gas porosity and in
ERIN DEDA, TRACY D. BERMAN, and JOHN E. ALLISON are with the University of Michigan, Ann Arbor, MI 48109. Contact e-mail: [email protected] Manuscript submitted October 3, 2016. METALLURGICAL AND MATERIALS TRANSACTIONS A
turn improve the mechanical properties.[3] To take full advantage of the property improvements provided by SVDC, there is a need for improved predictability of properties. In order to better predict location-dependent properties in castings, integrated computational materials engineering (ICME) approaches are under development.[12] Currently, two approaches exist to capture and reduce variations in properties—‘‘quality mapping’’ statistical approaches and deterministic physics-based structure–property relationships. Quality mapping is an empirical approach currently used to capture spatial property variation within a casting using highly calibrated parameters.[13–15] Since the quality mapping approach is not physics-based, it can be difficult to extrapolate results beyond the range of model calibration. This approach also requires a large quantity of experimental data. Thus, further study of the fundamental effects of microstructure on the tensile properties is needed to develop physics-based models for use in more refined ICME tools. Recently, deterministic yield strength models have been developed by Yang et al., Sharifi et al., and Toda-Carabello et al.[16–18] These models incorporate known strengthening mechanisms, specifically grain boundary, solid solution, and dispersion strengthening, but use different methods to calculate each strength component.[19] To better understand the mechanical properties, it is important to understand both intrinsic and extrinsic microstruc
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