Correlation of Positron Annihilation Parameters with The Mechanical Properties of Some Al Alloys

Abstract

In the present thesis, the studied samples are Al-5wt%Si alloy. All samples were annealed for homogenization at 550 C for 60 h and then were cut into squares of 1cm side and 1.25 mm thickness. After solution heat treatment at 550 C for 2 h, to produce the α- solid solution phase, the specimens were quenched into cold water at 0 C and immediately aged at different aging temperatures, Ta (200, 250, 300 and 350 C) for various periods of time, ta (15, 30, 60 and 120 min) followed by water quenching at 0 C. The positron annihilation spectroscopy has been applied to study the properties and defect structure of Al-5wt%Si alloy at different aging temperatures and aging times. The results are confirmed by means of scanning electron microscopy and Vickers microhardness measurements at room temperature. The experimental apparatus for the lifetime measure-ments is fast- fast timing coincidence set- up consisting of two plastic scintillator and characterized by a time resolution of 240 ps (FWHM) for 60Co. All Vickers microhardness measurements were taken at room temperature by using a Shimadzu 2 series microhardness tester with a pyramid shaped diamond indenter. All obtained spectra were analyzed using the LT 9 code to extract the following positron annihilation parameters: the lifetime components of positrons in free and bound states (τ1& τ2) and their intensities (I1& I2). The third component τ3 represents the formation of positronium at the surface layer of the sample; it could be neglected for alloy samples. X-ray diffraction patterns (XRD) were used for microstructural characterization for Al-5wt%Si alloy at different aging temperatures and times shows that no lines corresponding to Si could be observed at aging temperature of 200 C but with increasing the aging temperature relative strong