Marzyeh Moradi

Investigation of Thin Wall Casting Made of Semi-Solid A356 Using Back Extrusion and Die Cast

Semi- solid forming is a new technology in recent decades that has a number of advantages over conventional casting routes. As a result of these advantages, semi-solid processes are less limited in the part geometry, mainly concerning the wall thickness. According to many researches on aluminum alloys, the evaluation of flow and die filling properties of alloys as well as their resulting mechanical properties which are depended on various process parameters are being investigated up to now. Semi- solid forming processes contain three main steps: feedstock manufacturing, reheating and forming. Feedstock quality and reheating have strong effect on success of forming procedure. In order to understand and describe forming behavior in the semi-solid state, two different tests have been studied in the same casting conditions. In this study, back extrusion and die casting processes were used to investigate the effect of section size and process on the mold filling. In the case of back extrusion process a cup shaped specimen and in the case of die casting process, a step die with different sections size were used. Microstructure of different sections of specimens were studied by optical microscopy to depict the effect of different variables on the quality of products.

Creation of ultrafine-grained surfaces by large strain extrusion machining (LSEM)

ABSTRACT Large strain extrusion machining (LSEM) is examined as a route for achieving controlled microstructure refinement at freshly generated surfaces in a single pass of the machining tool. It is shown that the extrusion ratio λ of LSEM, which is the ratio of the thickness of the chip to that of the preset depth of cut, controls the extent of the ultrafine-grained (UFG) zone. Microstructure analysis was performed using orientation imaging microscopy (OIM) and mechanical testing using nanoindentation was used to characterize the UFG microstructure beneath the freshly generated surfaces. The mechanics of deformation in LSEM were examined using infrared thermography and modeled. The present research demonstrates LSEM as a novel platform for tailoring surficial microstructures and controlling their spatial extents in fabricated components.

Characterization of Deformation Mechanics and Microstructure Evolution During Indirect Extrusion in Small Length Scales

In situ characterization of mechanics of deformation including dynamic strain, strain-rate and rotation of material elements was performed in prototypical small length-scale forming operation- indirect extrusion (IE) of commercially pure Lead (Pb) and Aluminum (Al 1100) using Digital Image Correlation (DIC) technique. Effects of scaling and deformation rate over a range of dimensions and velocities on mechanical response of CP Pb and the resultant anomalies were studied. Additionally, previous and post-deformation characterization of microstructure in Al was accomplished by performing Orientation Imaging Microscopy (OIM) on workpiece materials with different grain sizes. Finally, In situ characterization aided by high speed imaging of indirect extrusion of Al coupled with a Visco-Plastic Self-Consistent (VPSC) model was used to predict the evolved textures in various regions of deformation zone and the results were compared to OIM observations.Copyright