Papers by Author: Mahmoud S. Soliman

Abstract: In the present investigation, annealed billets of commercially pure Al (1050) with coarse-grained microstructure of 0.6 mm were ECAPed through a die with an internal angle of 90o using two routes A and BC. The samples were processed up to four passes using both routes. The change in the processing route results in the change of the shear plane, and consequently the change in the produced microstructure. The microstructure study was conducted on the extrusion direction and the shear plane. The cell size, misoriention and the fraction of high angle boundaries were determined by using electron back scattered diffraction (EBSD). A study of mechanical behavior was conducted by cutting tensile and compression specimens from the ECAPed specimen in the extrusion direction to study the effect of processing route and the number of passes on the deformation characteristics. Enhanced strength was observed but with anisotropic behavior between tension and compression. Cyclic deformation under load control (HSF) was also performed and the S-N curves were established as a function of number of passes and processing route. The fractography of fractured tensile specimens was also investigated.

Abstract: Electron back scattered diffraction (EBSD) was used to document the microstructure and texture developed due to cross deformation of commercial purity 1050 aluminum alloy. The materials was first deformed in equal channel angular pressing die (ECAP) to one and two passes, via route BC and then deformed in plane strain compression (PSC) to two axial true plastic strain values of 0.5 and 1.0. The study provides a documentation of the evolution of microstructure parameters namely; cell size, misorientation angle, fraction of submicron grain size and fraction of high angle grain boundaries. These microstructure parameters were investigated on the plane normal to the loading direction in PSC (RD-TD). These microstructure parameters are compared to those achieved due to the ECAP process only. The ideal rolling texture orientations are depicted and crystal orientation maps were generated. The spatial distribution of grains having these orientations are revealed through these maps. The fraction of the main texture components for a 10o spread around the specified orientations is experimentally calculated and a quantitative idea on the evolution of microtexture is presented.

Abstract: Friction stir welding (FSW) is a fairly recent technique that utilizes a non-consumable rotating welding tool to generate frictional heat and plastic deformation at the welding location in the continuously-fed work piece. In the present investigation this welding process is applied to join 1050 cold-rolled aluminium plates. The effects of varying the welding parameters namely welding speed [56, 90 and 140 mm/min] and tool rotational speed [850 and 1070 rpm] on the mechanical and microstructural properties were studied. Vickers micro hardness results across the weldment showed that the weld nugget hardness is dependant upon the welding speed and the tool rotational speed. Increasing the welding speed at 850 rpm reduced the hardness at the weld nugget, whereas, at 1070 rpm the weld nugget hardness merely did not change. However, the hardness achieved at 850 rpm was constantly higher than that achieved with 1070 rpm irrespective to welding speeds. In the same fashion, the yield and ultimate strengths of the joints were influenced by varying the welding parameters. Increasing the welding speed at 850 rpm reduced both strengths whereas; at 1070 rpm they were almost unchanged. Microstructural study showed that the weld region is composed of unaffected base metal and the stir zoned [weld nugget] which is characterised by a fine equiaxed grain structure. Increasing the welding speed at constant tool rotational speed has caused a slight refinement in the weld nugget's grain size, whereas, decreasing the rotational speed has also led to weld nugget grain refinement.

Abstract: High-temperature deformation of an artificially aged 6082-Al alloy was conducted in the present investigation. Tensile tests were carried out at temperatures of 623, 673 and 723 K at various strain rates ranging from 5x10-5 to 2x10-2 s-1. The behavior of the alloy is characterized by high stress exponent, n and high apparent activation energy, Qa that are higher than what is usually observed in Al and Al solid-solution alloys under similar experimental conditions, which implies the presence of threshold stress; this behavior results from dislocation interaction with second phase particles. The threshold stress, σo values were seen to decrease exponentially with temperature. By incorporating the threshold stress in the analysis, the true activation energy, Qt was calculated to be close to that of dislocation pipe diffusion in Al. Analysis of the experimental data of the alloy in terms of the Zener- Hollomon parameter vs. normalized effective stress, revealed a single type of deformation behavior with an n value of ~7. Measurements showed that the values of elongation percent at failure increase with strain rate and temperature.