[01] E. E. Abdel-Hady, Physics Department, Faculty of Science, Minia University, Minia, Egypt. [02] A. F. Abd El-Rehim, Physics Department, Faculty of Science, King Khalid University, Abha, Saudi Arabia; Physics Department, Faculty of Education, Ain Shams University, Roxy, Cairo, Egypt. [03] S. M. Diab, Physics Department, Faculty of Education, Ain Shams University, Roxy, Cairo, Egypt. [04] Sh. M. Kandeal, Physics Department, Faculty of Education, Ain Shams University, Roxy, Cairo, Egypt.

The present study aimed to investigate the influence of heat treatment on the microstructure and mechanical properties of Al-5wt% Si alloy by positron annihilation spectroscopy and Vickers microhardness measurements. 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 for various periods of time. All of the samples were then characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) analysis as well as by hardness tests. The results revealed that the average life time, _av, and hardness, H_v, 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 H_v decreased with increasing aging temperature. A positive correlation was found between the positron annihilation parameters and the macroscopic mechanical properties through the measurements of Vickers microhardness for the samples. The lattice strain, η, average crystallite size, d, and dislocation density, δ, parameters deduced from the analysis of X-rays diffraction patterns were found to be consistent with the calculated mechanical data and positron annihilation parameters. The variations in _av and H_v 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.

Al-Si Alloys, Positron Annihilation Life Time, Vickers Microhardness

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