Papers by Keyword: Pore Closure

Abstract: Inner cavities in cast ingots have to be closed by means of open-die forging to guarantee the integrity of the forged components during usage. In the paper a differentiation is made between the macroscopic and the microscopic closing of natural inner cavities. Special attention is paid to the dendritic structure of the surfaces of inner cavities and their impact on the microscopic closing behavior. Additionally, investigation showed that a closing on the microscopic scale is only possible if the cavities do not come in contact to the atmosphere during hot forming. For the analysis of the cavity closing, ingots of a heat-treatable, hot-working and a cold-working steel were used. The ingots were cast, forged and the surface of the inner voids was analyzed with the help of light-microscopy, SEM and EDS for the microstructure and by using tensile tests on macroscopic scale. Also, numerical investigations were a part of the work, whereby the parameters void size, void shape and anvil-shape were varied. As a result of the numerical investigation, a so called closing function was formed. This function enables the user to calculate the necessary height-reduction for closing of inner cavities of the regarded ingot format.

Abstract: This paper revolves around the idea of finding the strength enhancement of pure ‘Al’ compacts processed through Equal-Channel Angular Pressing (ECAP) process which ultimately results in fine grain structure of the material processed. The material initially prepared through conventional powder metallurgical route is processed in an ECAP die with a channel angle of 110⁰. The tensile test and micro-structural evaluation is done following the ECAP process and it is found that there was a substantial enhancement in the tensile properties and Ultrafine Grain (UFG) structure is obtained due to the Severe Plastic Deformation (SPD) phenomenon taking place during the process. The pore closure behavior is also analyzed using the TEM micrographs after each pass in ECAP die and promising results are obtained when the material is processed through different routes. The dislocation cell structure is also found to get refined after each pass through the die. The pore closure behavior is also confirmed using the DEFORM 3D software when the aluminum is simulated under similar conditions.

Abstract: Although forming of porous metal is demanded for industrial applications, the deformation characteristics have not been investigated sufficiently. In this study, lotus-type porous copper is processed by multi-pass cold rolling. At the early stage of rolling, the elongation of the porous copper in the rolling direction is small, and the porosity decreases almost linearly with the total reduction in thickness. It is found that pass schedule with small rolls and with small reduction per pass is effective to suppress pore closure. Hardness of the porous copper increases almost linearly with total reduction. If the effective total reduction is considered, the hardness change is similar to that of a nonporous copper.