Papers by Author: M.A. Abdel-Rahman

Abstract: The aim of this work is to establish a correlation coefficient between the positron annihilation lifetime technique (PALS) and the Vickers hardness for the heat treatable aluminum alloys (6066, 6063).The potential of positron annihilation spectroscopy in the study of light alloys is illustrated with special regards to age hardening, severe plastic deformation, annealing and quenching in aluminum alloys. Vickers hardness is the standard method for measuring the hardness of metals, particularly those with extremely hard surfaces. Accordingly, a correlation coefficient of 90 % between τ and Hv is obtained. This correlation can help us to explain many behaviors of these alloys under deferent conditions.

Abstract: The electrical resistivity and the corresponding mechanical properties (hardness) of some 5xxx Al-Mg alloy processed by plastic deformation were investigated. Plastic deformation was performed at room temperature. Isothermal annealing produced a significant change in both the electrical and mechanical properties of the samples. As the annealing time was increased, the resistivity and hardness up to full recovery. The activation enthalpy of migration of defects was determined, was found to be 0.234±0.06 eV, 0.218±0.049 eV, 0.316±0.016 eV 0.232±0.012 eV for 5005, 5251, 5052 and 5754 alloys, respectively.

Abstract: The result of positron lifetime measurements of a defected 5251 Al alloy is reported. Positron lifetime is measured as a function of the thickness reduction of the sample which shows a nearly linear increase and then becomes constant; which can be considered to be a reason for the defect movement saturation. The trapping rate, trapping efficiency, trapping cross-section, defect concentration and defect density of positrons are also measured for the sample concerned. The behaviors of these parameters are matched with theoretical calculations. Data are analyzed using the PATFIT88 computer program.

Abstract: Defects are central to any understanding of material characteristics. They determine a host of material properties, including strength, ductility, resistivity and opacity. Positron annihilation spectroscopy (PAS) is a well-established high-sensitivity technique for detecting defects in solids. In this work, we study the influence of plastic deformation on the properties of 5754(AlMg3) aluminum alloy.

Abstract: The Electrical Resistivity and a Mechanical Property (hardness) of some 5xxx Aluminum Alloys Were Investigated. the Samples Were Exposed to a Type of Plastic Deformation (compression) to Nearly40% Deformation; the Resistivity and Vickers Hardness Being Measured for Every Degree of Deformation. the Investigated Alloys Gave a Good Response to the above Two Techniques, and the Results Were Consistent with each other.

Abstract: The Objective of this Research Was to Investigate the Use of a Sensor System to Monitor Continuously the Defect Formation Response of Heat-Treatable Aluminum Alloys. the System Continuously Monitors a Material Property, Resistivity, which Is Indicative of the Quenching Process. such Studies Will Allow us to Gain Active Control of the Aging Process and Hence the Material Properties of Aluminum Alloys.

Abstract: Positron annihilation techniques (PAT) have recently been successfully employed for the characterization of phase transitions in metals and compounds. In the present study, positron annihilation lifetime (PAL) measurements have been carried out on a nanocrystalline titania (TiO2) in the form of powders that had been heat-treated at temperatures ranging from 300 to 1273K. The PAL spectra were analyzed into two lifetime components. The shorter lifetime τ1 (185-300 ps) is attributed to positron annihilation in vacancies and the longer lifetime τ1 (400-580 ps) to positrons in microviods at interfaces. The rutile phase of TiO2 powders was utilized as a reference in order to compare their behavior with the commercially supplied and widely available anatase phase (Degussa P25). The influence of the heat-treatment upon the nanostructure during the transition of the anatase to rutile phase were also investigated by X-ray diffraction (XRD), TEM and BET surface area methods. Understanding of this effect is expected to enhance our knowledge of the morphology and nanocrystallite size of TiO2 powders and their T-dependence, and hence their physical properties.

Abstract: A comprehensive and systematic study using PALS technique, Vickers hardness test and electrical LCR meter were undertaken to follow property development during the recently promoted interrupted ageing treatment for 2024 aluminum alloy. In this work, solution heat treatments at different temperatures were performed in aircraft materials 2024 aluminum alloy. This work describes the development of the dependence of mechanical, electrical properties of 2024 Al-alloys on heat treatment to characterize microstructural changes during heat treatment. PALS, mechanical and electrical testing will be used to measure the features of the material as a function of time for each ageing temperatures.

Abstract: Positron annihilation lifetime (PAL) is one of the most important nuclear techniques used in material science. Electrical measurements are also used in material science. Samples of 25 % deformation have been used for these studies. Both positron annihilation lifetime and electrical measurements were used to determined the activation energy of migration the dislocation in 7075 alloy. The isothermal annealing measurements were performed at 643, 663, 683 and 703 K. The activation energy of migration the dislocation are obtained as 1.35 ± 0.16 eV and 1.25 ± 0.05 eV for positron annihilation lifetime and electrical techniques respectively.

Abstract: Positron annihilation lifetime (PAL) measurement is one of the most important nuclear techniques used in materials science. Electrical measurements are also used in materials science. Both PAL and electrical measurements were used here to determine the activation energy of migration of dislocations in one of the most important engineering aluminum alloys: 2024. Samples of 25% deformed (thickness reduction) material have been used for these studies. The isothermal annealing measurements were performed at 583, 603, 623 and 643K for both techniques. The activation energy of migration of the dislocation was found to be equal to 1.24 ± 0.08eV by using PAL measurements and to 1.35 ± 0.01eV by using the electrical technique.