Effect of impurities and microstructure on the mechanical properties and ultrasonic attenuation of alumium

摘要

The present work is concerned with expermental study of the relaxation and the grain size dependence on the yield stress of two groups of poly crystalline aluminum specimens, namely commercially pure aluminum and AL-Mg-Si alloy. These two kinds of specimens were subjected to the same degree of deformation about 75 reduction in cross section area and were given the same amount of heat treatment by annealing for two hours at 200, 300, 500 and 600 degree. The experimental part of the relaxation phenomena investigation dealt with the measurement by U.S. attenuation using pulse echo technique. These measurements were carried out in the temperature range from (-160 degree to zero) at frequencies (2,4,6 and 10 MHz). The activation encrgy for each process was calculated. A conventional tensile testing machine was used for mechanical testing to attain the load-elongation curves at different working temperatures and different grain diameter for the two tested groups. The results showed the relation between the activation energy and the annealing temperature with the lengths of dislocation segments. The grain size dependence on the yield stress was discussed in the view of the incompatibility stress which arise between the grains and its neighbors.