الفهرس 
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Abstract
In this work; 2024(Al-Cu-Mg), 7075 (Al-Zn-Mg-Cu-Cr) and 3003(AI-Mn-Si) AI-alloys are investigated. Linear defects are introduced in the specimens using a hydraulic press, while thermal defects are introduced through heat treatments of the alloys. All measurements are carried out at room temperature.
Positron annihilation technique (PAT) is known to be a very sensitive and nondestructive tool for stu ying the defect structure in materials. It has been used to probe a variety of material properties and has been widely employed in solid state physics and materials science research. The main assumption of the simple trapping model is that positrons annihilate in a solid from a free or trapped state. The software used for analyzing positron annihilation lifetime spectra is known as P ALSfit. It is composed of two modules; Positron Fit and Resolution Fit, for fitting positron lifetime spectra. In both modules, a model function is fitted to a measured lifetime spectrum. This program is built upon the well tested P A TFIT package.
Electrical resistivity is a fundamental property of every conducting material and is a critical parameter in materials research. Hence, it is a key physical property of all materials. In this study LCR meter, as well as other simple Ohmic circuits, were used to characterize the resistivity of aluminum alloys. Such characterization requires the measurement of very low resistances and therefore very small voltages are expected to be measured accurately.
Measurement of the macro-hardness of materials is a quick and simple method for obtaining mechanical property data of the bulk material from a small sample. It is also widely used for the quality control of surface treatment processes. However, when concerned with coatings and surface properties sensitive to friction and wear processes, for instance, the macro-indentation depth would be too large relative to the surface-scale features. Micro-hanlness is the hardness of a material as determined by forcing an indenter such as a Vickers indenter into the surface of the material under 15 to 1000 gf load.
For Natural ageing, the solution treatments were carried out In an air circulating furnace at three different temperatures. Samples were quenched into water at 2 °c. Gen~rally, an important hardness increase and a slighf positron lifetime decrease were observed during pre-ageing. In the natural ageing of the alloy 2024, It was found that Vickers number reaches its maximum value (155 Hy), the resistivity reaches its maximum value (4.47 x 10-6 n.m) and the mean lifetime reaches its maximum value (195.5 ps) for samples quenched at 7730 K. For the natural ageing of alloy 7075, the resistivity reaches its maximum value (13.17x10-6 n.m) at 7730 K while the mean lifetime reaches its maximum value (216.9 ps). at 7230 K.
Mechanical alloying increased the hardness of aluminum based alloy in the as-extruded condition as well as after all heat treatments. The nuclear and electrical techniques were used to determine the activation energy for formation- of thermal defects, it was found to be 0.69 ± 0.09 eV and 0.64 ± 0.09 eV by PALS and electrical techniques, respectively. Also, the obtained values of the activation energy for migration of the dislocation in 2024 using PALS and electrical techniques are found to be 1.24 ± 0.08 eVand 1.35 ± 0.01 eV, respectively. For 7075 alloy, the obtained values of the activation energy for migration the dislocation using PALS and electrical teclmiques are found to be 1.35 ± 0.16 eV and 1.25 ± 0.05 eV respectively. It is found that, the 2024 alloy includes both point defects and dislocations regions while 7075 alloy includes the dislocations region. Also, it was observed that the recovery range of dislocation for 7075 alloy is much higher than the range of dislocation for 2024 alloy.
For the 3003(AI-Mn-Si) alloy, as deformation increases, the concentration of defects increases but the mean lifetimes saturated and didn’t increase because almost all positrons are annihilated. The defect density and grain size are calculated. [Trapping rate = 21.8x 109 S,I, Trapping efficiency = 6.5x 1 O’ 8(cm3 S•I) and Trapping cross section = 3.5x19,17 cm2]. The grain size decreases exponentially from 0.22 11m at 2 % deformation to 0.1008 11m at 41 % deformation but the defect concentration increases from 437.65xl012 cm,3 at 2 % deformation to 722.72x 1015 cm’3 at 56 % deformation.
In X-ray diffractogram of the deformed 2024 alloy, the . relation of FWHM versus Bragg angle showed the effect of plastic deformation on the sample. Also, the grain size results using the XRD technique.