The Effects of Silicon Addition on the Microstructure and Mechanical Properties of a Mg-Al-Sn Alloy Produced by Vacuum Assisted High Pressure Die Casting
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In this paper, the effects of a small addition of Si (about 0.4 wt pct) on the microstructure and mechanical properties of a Mg-Al-Sn alloy produced with vacuum assisted high pressure die casting (HPDC) are reported. CALculation of PHase Diagrams-based modeling was used to design the heat treatment schedules to optimize the precipitation of Mg2Sn and Mg17Al12 in the Mg-7Al-2Sn-0.4Si alloy (in wt pct, designated as ATS). The HPDC test specimens were studied in the as-cast condition as well as in multiple heat-treated conditions to improve their tensile properties. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) techniques were used to characterize the microstructure in each condition. The results suggest that the small addition of Si is effective in enhancing and accelerating the precipitation hardening of Mg-7Al-2Sn alloy AT72, due to enhanced precipitation of Mg17Al12 and Mg2Sn phases as well as the precipitation of Mg2Si phase. In as-cast conditions, the new ATS alloy has similar strengths but significantly improved ductility compared with AZ91D, and significantly improved strength but reduced ductility compared with AM60B. The ATS-T6 after a one-stage solution treatment provides further improvement of mechanical properties: yield strength 151 MPa, ultimate tensile strength 253 MPa, and elongation 4.9 pct.
The authors would like to acknowledge the collaboration with General Motors and many helpful discussions with Drs. Jon Carter and Anil Sachdev of GM R&D Center and Dr. Renhai Shi of The Ohio State University. Part of this work is supported by the United States Department of Energy under Awards DE-EE005753 and DE-EE0006450. This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof. ANDREW D. KLARNER and WEIHUA SUN were with the Department of Materials Science & Engineering, The Ohio State University, Columbus, OH, when this work was carried out.
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