Interstitial-impurity trapping in Al-Fe and Al-Zn

Ultrasonic attenuation and velocity measurements were made as a function of polarization, temperature, frequency and annealing before and after electron irradiation near 65K of A1-Fe and A1-Zn dilute alloys. Multiple relaxation processes were observed in both alloys. In the case of A1-Zn, the simultaneous annealing near 130K of resistivity, diae1astic modulus changes, and a parae1astic relaxation peak in C' allows for a characterization of the individual defects. The results provide strong evidence that below 130K, the -mixed dumbbell is the predominant interstitial trapping configuration. The temperature dependence of the relaxation peak near 4.9K is not that expected for a thermally activated process, but provides instead evidence for defect tunneling. A second trapping configuration present in low concentration anneals out near lOOK, and probably arises from -mixed defects. In A1-Fe, the observation of the diae1astic effect and a peak in the C' mode not previously seen in earlier internal friction measurements, together with an identification of this peak with the major defect species resolves the apparent contradiction between the internal friction and channelling symmetry evidence. This also allows for an interpretation in terms of a -mixed dumbbell which is consistent with previous theory and channelling and Mossbauer measurements. The results for AI-Fe differ greatly from those obtained earlier for AI-Mn, suggesting that current theories based only on size differences require extension.U of I OnlyThesi