Papers by Author: Wojciech Z. Misiolek

Abstract: AZ 31 Magnesium alloy was extruded under industrial conditions into both a solid shape and a hollow profile. A microstructure analysis of the solid shape revealed a bimodal grain distribution. The FEM process simulation was performed for double hat hollow profile, extruded through an eight-port-hole die using the modified flow stress model from literature. This allowed us to make a prediction of the extrusion process state variables. Additionally, a numerical simulation revealed some shortcomings in terms of a lack of predictive capabilities for extrusion welding. The integrity of the welds was analyzed using metallography techniques. The search for better mechanical properties has propelled alloy development research. Workability evaluations of new Magnesium alloys ZE20, ZE50 and ZE80 containing Zinc and Cerium were performed using compression tests under various temperature and strain rate conditions.

Abstract: Butt welded joins were produced between commercially pure (CP) titanium and various titanium alloys using an electron beam welding technique. The materials used were CP Ti, Ti-6Al-4V (Ti64) and Ti-5Al-5V-5Mo-3Cr (Ti5553). Grain boundary structures, mechanical properties, compositional profiles across the welds and fracture modes are presented. CP Ti has always been known for its excellent weldability, Ti64 has good weldability and, preliminary results indicated that Ti5553 alloy is also weldable.

Abstract: Solid-state welding takes place during the extrusion of hollow shapes and tubes made from selected metals such as aluminum and magnesium and their alloys. DEFORM^TM is one of the most frequently used FEM software packages to analyze the metal flow in deformation processes. However, it has some limitations while applied to study the extrusion welding. The 2D and 3D versions of DEFORM^TM cannot determine if extrusion welding takes place in a port-hole die. This limitation is a result of a lack of ability to transfer the localized deformation conditions to a judgment about a good or poor weld. In this work, a new modeling method has been proposed to obtain the localized information at the extrusion welding seam. A so-called pressure plate was virtually inserted in the position of the extrusion welding seam, which plays a role of a sensor and has recorded all the information at the given seam during the entire extrusion process. Analytical methods have been utilized to study the data collected from this sensor to evaluate the probability of the formation of the sound extrusion welding seam. The generated results have been used to verify Plata & Piwnik extrusion welding criterion and can be implemented into existing extrusion models to achieve better prediction of weld integrity.

Abstract: The extrusion process provides conditions for non-uniform metal flow depending on strain, strain rate and temperature of deformation as well as deformation zone geometry. As a result of these conditions significant microstructure gradients are present within the extrudate. The extreme case of the microstructure gradient is a formation of the peripheral coarse grain structure (PCG). This phenomenon is present in many structural aluminum alloys extrudates and its presence should be eliminated or at least significantly reduced because of the mechanical properties and aesthetic points of view. A number of experiments, including physical and numerical simulations, were performed in order to understand and model the origin of the PCG in indirect extrusion of 6xxx alloys. These experiments included different alloy chemistry, various temperatures, extrusion ratios and extrusion speeds allowing analysis of their influence. Parallel to the experimental results the numerical simulation of the metal flow showing the origin of the metal in different extrudate location was performed using software package DEFORM TM. A review of performed research will be followed by the analysis of the results and discussion of future needs.