A numerical model was developed for the prediction of flow stress evolution and high temperature extrusion formability for a new high ductility magnesium alloy with primary alloying elements of 2.4 %wt. Zn and 0.2 %wt. Ce, designated as ZE20. The ultimate goal for the implementation of the model is for the prediction of extrusion properties of this new alloy; the study presented herein proved to successfully simulate the flow stress evolution and extrusion behavior of the ZE20 magnesium alloy in a range of conditions verified by physical experiments. Hot compression flow stress experiments were carried out for the determination of the plastic deformation characteristics of the new alloy at strain rates and temperatures typically encountered in industrial extrusion forming of magnesium alloys. Additionally, indirect and direct extrusion experiments were designed, simulated, and carried out for development of, and comparison with, the numerical model for simulation in DEFORM-3D™. Ultimately, it was shown that the numerical model accurately predicted high-strain plastic flow stress values as compared with experiments for the new alloy as well as strain, strain rate, and temperature values within the formed extrudate, which are consistent with previous studies and microsctructural findings for this material having undergone high temperature extrusion processing. Specifically, a uniform, equiaxed, fully recrystallized microstructure was observed across longitudinal weld seams in a hollow experimental automotive beam extrudate. It was shown that the temperatures developed within the billet in the weld chamber reach sufficiently high enough levels to drive full recrystallization and, thus, superior seam weld quality. It was also predicted by the model, and verified by physical results, that there is a threshold for extrusion speed for this particular alloy, at fixed tooling conditions. It has thus been demonstrated that the numerical flow stress model package developed for implementation in deformation software simulation packages such as, but not limited to, DEFORM-3D™ accurately predicts strain, strain rate, and temperature conditions for high temperature forming operations of the new magnesium alloy ZE20, allowing for the design of industrial processes which can produce high quality microstructure and mechanical properties in extruded solid or hollow profiles.
|Advisor:||Misiolek, Wojciech Z.|
|School Location:||United States -- Pennsylvania|
|Source:||DAI-B 80/03(E), Dissertation Abstracts International|
|Subjects:||Engineering, Mechanical engineering|
|Keywords:||Extrusion, Magnesium, Modeling|
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