الفهرس 
CHAPTER 1: Introduction and Aim of the WorkOnly 14 pages are availabe for public view
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Abstract
This thesis is devoted to investigate the effect of heat treatment on the evolution of microdefects of Al-5wt% Si alloy by positron annihilation spectroscopy (PALS) and find a correlation between positron annihilation parameters in Al-5wt% Si alloy and Vickers microhardness measurements (Hv) at room temperature (RT). Samples of Al-5wt% Si alloy were treated with a T6 heat treatment, that is, solution treatment at 550 C for 2 h, quenching in cold water at 0 C, followed by aging at different temperatures Ta (200, 250, 300 and 350 C) for various periods of time ta (15, 30, 60 and 120 min). All of the samples were then characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) analysis as well as by hardness tests at room temperature. The results revealed that the average life time, av, and hardness, Hv, continuously increased with increasing aging temperature at lower aging times (15 and 30 min). At higher aging times (60 and 120 min), both av and Hv decreased with increasing aging temperature. The variations in av and Hv with increasing aging time and aging temperature have been explained in terms of the formation and/or dissolution of Si precipitates of different number and size.
Keywords: Al-Si Alloys, Positron Annihilation Life Time, Vickers Microhardness, X-ray diffraction, Scanning electron microscope.