Papers by Author: M. Abdel-Rahman

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Authors: Emad A. Badawi, M.A. Abdel-Rahman, Alaa El-Deen A. El-Nahhas, M. Abdel-Rahman
Abstract: Many Aluminum-based alloys are strengthened by using a heat-treatment process known as age-hardening. The aim of this work was to produce a high-strength 6xxx-series Aluminum alloy by adjusting the processing conditions, namely solutionizing and artificial aging. It consists of heating the alloy to a temperature at which the soluble constituents will form an homogeneous mass via solid diffusion, holding the mass at that temperature until diffusion takes place, then quenching the alloy rapidly to retain the homogeneous condition. In the quenched condition, heat-treated alloys are supersaturated solid solutions that are comparatively soft and workable, and unstable, depending upon the composition. After solution treatment and quenching, hardening is achieved either at room temperature (natural aging) or via a precipitation heat treatment at a suitable temperature (artificial aging). Precipitation heat treatments are generally low-temperature, long-term processes. Temperatures range from 115 to 190C; times vary from 5 to 48 h. The choice of time-temperature cycles for precipitation heat treatment should receive careful consideration. The objective is to select the cycle that produces an optimum precipitate size and distribution pattern. The mechanical characterization of heat-treatable 6xxx (Al-Mg-Si-Cu based) 6066 wrought aluminum alloys was studied. Their effects were investigated in terms of microstructure using positron annihilation lifetime techniques and monitoring the mechanical properties by mean of Vickers hardness measurements. The hardness is the resistance of a material to plastic deformation, and gives it the ability to resist deformation when a load is applied. The greater the hardness of the material, the greater resistance it has to deformation. The Vickers hardness of 6066 alloy has its maximum value (98) when aged for (10) hours at (175C) after quenching at 530C; so this temperature is the solution temperature of this alloy .The hardness conformed to reference values.
Authors: M.A. Abdel-Rahman, N.A. Kamel, M. Abdel-Rahman, M. Abo-Elsoud, Yahia A. Lotfy, Emad A. Badawi
Abstract: Positron Annihilation Doppler Broadening Spectroscopy (PADPS) is one of the nuclear techniques used in material science. PADPS measurements are used to study the behavior of defect concentration and dislocation density in a set of 3003 and 3005 wrought aluminum alloy. It has been shown that positrons can become trapped at imperfect locations in solids. The S-parameter can be influenced by changes in the concentration of such defects. There is no observed change in the Sparameter values after the saturation of defect concentration. The S-parameter and trapping rates for the samples deformed up to 10 percent were studied. The concentration of defect range varies from 1017 to 1018 cm-3 and from 1016 to 1017 cm-3 for 3003 and 3005 wrought Al alloy respectively. While trapping rate range varies from 1 x1010 to 1.2x1011 s-1 for 3003 and from 1 x109 to 1.2x1010 s-1 for 3005 wrought Al alloy.
Authors: M. Abdel-Rahman, N.A. Kamel, Yahia A. Lotfy, Emad A. Badawi, M.A. Abdel-Rahman
Abstract: Positron Annihilation Doppler Broadening Spectroscopy (PADPS) is a nondestructive technique used in materials science. Electrical measurements are one of the oldest techniques also used in materials science. This paper aims to discuss the availability of using both PADPS and electrical measurements as diagnostic techniques to detect defects in a set of plastically deformed 5454 wrought aluminum alloys. The results of the positron annihilation measurements and the electrical measurements were analyzed in terms of the two-state trapping model. This model can be used to investigate both the defect and dislocation densities of the samples under investigation. Results obtained by both nuclear and electrical techniques have been reported.
Authors: M. Abdel-Rahman, Yahia A. Lotfy, M.A. Abdel-Rahman, Emad A. Badawi
Abstract: Positron Annihilation Spectroscopy (PAS) is a powerful and versatile tool for the study of the microscopic structure of materials. Doppler Broadening Positron Annihilation Technique (DBPAT) is the fastest technique used among positron annihilation techniques. The dose effect in Al-6.5at. % Cu alloy was investigated by means of DBPAT. An abrupt change in both the S and W line-shape parameter values occurred at 70 kGy of irradiation. The S- and W-Parameters of the trapped positrons at 70 kGy of γ−irradiation dose are about 48 % and 14 % respectively. The S- versus W-parameter reveals a linear relationship indicating the presence of only one type of defect. The S- and W-parameters have been used in the determination of the positron trapping rate and the grain size of the AlCu6.5 alloy.
Authors: M.A. Abdel-Rahman, M. Abdel-Rahman, N.A. Kamel, M.S. Abdallah, Emad A. Badawi
Abstract: Positron annihilation has been performed in order to study the isochronal annealing of wrought (2024, 7075) and cast (AlSi11.35Mg0.23, AlSi10.9Mg0.17Sr0.06) aluminum alloys, at temperatures ranging from RT to 773K, after having been deformed at RT to 25% deformation. Two annealing stages of the microstructures were distinguished, which were attributed to recovery in (2024, AlSi11.35Mg0.23, AlSi10.9Mg0.17Sr0.06) due to point defects and dislocations, respectively, and only one (due to dislocations) in (7075). Also, natural aging for up to more than 650 days was studied as a function of mean lifetime.
Authors: M. Abdel-Rahman, Ahmed G. Attallah, M. El-Sayed, A.A. Ibrahim, A.A. Akel, Atef E. Ali, Emad A. Badawi
Abstract: Certain radioactive isotopes decay by emitting positrons, and the positrons can be used to probe the structure of solid materials. For example, one can investigate the grain size due to deformation in a metal. XRD is also a powerful technique for detection the defects introduced into a metal and for investigating the microstructure of a deformed metal. In this paper we shall investigate the plastic deformation effect on the grain size of 5251 Al alloys using two different techniques, PALT and XRD. The study shows a significant effect of the plastic deformation on the grain size which decreases as the deformation increases.
Authors: Emad A. Badawi, M.A. Abdel-Rahman, E.M. Hassen, M. Abdel-Rahman, M.O. Abdel-Hamed
Abstract: A description of positron annihilation spectroscopy (PAS) in solids is given in terms of a trapping model. Data are presented for a commercial AA1050 dilute alloy ingot, and fitted to a model allowing presentation in the form of Arrhenius plots. From whence the value of the activation enthalpy, , for thermal vacancies obtained by PAS for AlFeSi is found to be 0.860.18eV.
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