الفهرس 
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Abstract
Point defects and dislocations are introduced into alloys under investigation by various methods:
1) Plastic deformation at room temperature (RT).
2) Quenching of samples from high temperatures to low temperatures in order to keep the defect configuration obtained at high temperatures. Several techniques were used for studying these defects and their properties (e.g., defect density, recovery stages, migration and formation energies, grain size, etc…)
Positron annihilation techniques are found to be a very sensitive probe for the investigation of those defects and their properties. Most of the positron annihilation work has been done on pure metals.
Measurements of positron annihilation on some commercial aluminum alloys, two wrought alloys 6063 and 6066 were carried out in this thesis.
Measurement of positron annihilation lifetime as a function of thickness reduction have been performed on a set of pairs for each of the alloys mentioned above (namely 6063 and 6066) plastically deformed at RT up to 40 % thickness reduction. The positron mean lifetime () behavior exhibits saturation for deformation larger than 5 % thickness reduction approximately. The mean lifetime, as measured at various degrees of deformation, giving trapped lifetime (τt) =234.78 ± 4.1, 221.68 ± 3.4 ps and free lifetime (τb) =186.4 ± 4.1, 195.0 ± 3.1 ps for samples mentioned above, respectively. Trapping efficiencies and trapping cross-sections were calculated for the investigated samples.
Measurement of positron annihilation mean lifetime (τ) as a function of quenching temperature are discussed, which results in the formation of thermal vacancies in samples were investigated between 323 and 723 K. Three regions of different slopes were observed for the mean lifetime. In the first region, the positron mean lifetime increases slowly and linearly with increasing the temperature from which the sample is quenched until some threshold temperature Tc (characteristic temperature), this linear increase in is ascribed to the thermal lattice expansion. In the second region at temperature higher than Tc, a strong non linear change of occurs. This change is attributed to trapping of positrons in thermal generated vacancies. In the third region at high temperatures, where there are many monovacancies produced in the sample, the mean lifetime value is saturated as a result of trapping of most positrons.
The formation enthalpy and the migration enthalpy of the thermal vacancies are estimated by the threshold method. Their values are in a good agreement with the previous studies.
The aim of the present part is to study the effect of artificial and natural aging on the hardness and mean lifetime of the heat treatable 6xxx (Al-Mg-Si-Cu based) 6063, 6066 wrought aluminum alloys;
1- In the study of artificial aging, it was found that the hardness of 6063 alloy has a maximum value of (58) Vickers number (V no.) upon its aging for (8) hours at (448K) after quenching from 793 K, which is the solution temperature of this alloy. wherever the Vickers hardness of 6066 alloy has a maximum value of (98 V no.) when it aged for (10) hours at (448K) after quenching from 803K, so this temperature is the solution temperature of this alloy.
2- In the study of natural aging, the Vickers hardness of 6066 alloy has a maximum value (80 V no.) after (10) days of quenching from 803 K. The hardness of 6063 alloy has a maximum value (40 V no.) after (14) days of quenching from 793 K.
A good correlation between the positron mean lifetime and Vickers hardness is found. This correlation can help in explanation of the behaviors of these alloys under different conditions.