الفهرس 
Chapter 1: IntroductionOnly 14 pages are availabe for public view
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Abstract
In this work the positron annihilation lifetime spectroscopy has been used to study the defect properties for 6082, 1070, and 6063 wrought Al-alloys under the effect of cold work (compression), annealing, and natural aging. X-ray powder diffraction data employing the Rietveld’s method of structure/microstructure refinement in addition to Vickers hardness test have been also used as comparative techniques.
The obtained results for 6082 Al-alloy showed an increase behavior for the value of the positron annihilation lifetime with thickness reduction up to 12% after which saturation in the lifetime measurements occur. Relating the experimental results of Positron annihilation lifetime spectroscopy (PALS) with the theoretical models lead to determining:
- The annihilation parameters such as trapping efficiency, trapping rate, trapping cross section and trapping coefficient for trapping in dislocations.
- The defect and dislocation densities were obtained as a function of the thickness reduction.
- The variation of the dislocation stored energy, grain size and micro-strain with the deformation degree.
Studying the effect of plastic deformation on the defect properties of 6082 Al-alloy by X-ray diffraction and Vickers micro-hardness showed good correlation with PALS measurements. The lattice parameter, crystallite size and r.m.s. lattice strain also determined from the analysis of X-ray powder diffraction data by Material Analysis Using Diffraction (MAUD) program.
The results for the effect of isochronal annealing on the defect properties of 1070 Al-alloy showed that the value of the positron annihilation lifetime in the trapped state (τt) (deformation 20%) was found to be 202.9 ps and it was gradually decreased to reach 165.6 ps at 573 K which is the same value of the positron mean lifetime in the defect free state (τf).
Isochronal annealing study by Vickers hardness showed that the alloy is recovered in a temperature range between 633 to 723 K. The dislocation and
defect densities have been already obtained by Vickers hardness measurements. The microstructure parameters also obtained from the analysis of X-ray powder diffraction data by MAUD program.
The effect of natural aging on the defect properties of 6063 Al-alloy was studied by positron annihilation lifetime spectroscopy (PALS), X-ray diffraction, and Vickers hardness.
The results showed that the positron mean lifetime for quenched samples in case of non-deformed and 5%, 30% deformation decreases exponentially with aging time, which gives information about the aging precipitation, and defect migration. In natural aging, the rate of clustering (precipitation) increase with the degree of deformation. The positron mean lifetime for non-quenched samples decreases with aging time; due to the migration of dislocations which produced by plastic deformation.
Vickers hardness (HV) test of the 6063 Al-alloy for sample deformed at 30 % is higher than the sample deformed at 5 % which is also higher than non-deformed samples as a function of aging time. The obtained results in Vickers hardness values as a function of aging time; gives information about age hardening and migration of dislocations produced by plastic deformation. The dislocation density calculated by hardness measurements reveal a decrease with aging time until about 50 hour is reached after which the dislocation density values are approximately saturated with increasing of aging time.
The lattice parameter, crystallite size and r.m.s. lattice strain have been obtained for 6063 Al-alloy with aging time from the analysis of X-ray powder diffraction data by MAUD program.
There is good correlation between results obtained by XRD, Vickers hardness test, and lifetime measurements as a function of aging time.