Papers by Author: Yahia A. Lotfy

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: 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: Many aluminum-based alloys are strengthened by 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 by 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 by precipitation heat treatment at a suitable temperature (artificial aging). Precipitation heat treatments are generally low-temperature long-term processes. Temperatures range from 115 to 190°C and times vary from 5 to 48 h. Choice of time-temperature cycles for precipitation heat treatment should receive careful consideration. The objective is to select the cycle that produces the optimum precipitate size and distribution pattern. The mechanical characterization of heat-treatable 6xxx (Al-Mg-Si-Cu based) 6063 wrought aluminum alloys was studied. Their effects were investigated in terms of the microstructure, using positron annihilation lifetime techniques and mechanical properties monitoring via Vickers hardness measurements. The hardness is the resistance of a material to plastic deformation, which gives it the ability to resist deformation when a load is applied. The greater the hardness of the material, the greater the resistance it has to deformation. The hardness of 6063 alloy has its maximum value (58) when aged for 8 hours at 175oC after quenching from 520oC; which is the solution temperature of this alloy. The hardness conformed to the literature. We also test the aging ability of the 1xxx aluminum alloy: 1050.

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.

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.

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.