EFFECT OF IMPURITIES ON THE INTERNAL FRICTION SPECTRUM OF MAGNESIUM AFTER PLASTIC DEFORMATION

We have studied the impurity effect on the internal friction spectrum, with two different samples magnesium 4N and magnesium 6N containing zinc and iron : - for the sample 4N we observe a broad peak depending on the oscillation strain amplitude : this peak shifts towards low temperature when the amplitude increases. - for the sample 6N containing zinc and iron, the internal friction spectrum is different form the one of the 6N sample previously mentioned. After annealing at 250 K we observe, at low strain amplitude, besides the B1and B2peaks, two other peaks situated around 100 and 150 K. But at a high strain amplitude we find the two peaks B1and B2as in the 6N sample. After annealing at 500 K the B1and B2peak are not observed but a large peak appears which shifts towards low temperature with increasing εmThis peak is specific on thermomechanical unpinning of dislocations