Berlin 2012 – scientific programme
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MM: Fachverband Metall- und Materialphysik
MM 7: Transport and Diffusion II
MM 7.2: Talk
Monday, March 26, 2012, 11:45–12:00, H 1029
The influence of Mg and Si atoms on the cluster formation process in Al-Mg-Si alloys studied by positron annihilation lifetime spectroscopy — •Meng Liu1,2, Yong Yan2, Zeqin Liang1, Cynthia Chang2, and John Banhart1,2 — 1Helmholtz-Zentrum Berlin für Materialien und Energie, Hahn-Meitner-Platz 1, D-14109 Berlin — 2Technische Universität Berlin, Hardenbergstr. 36, D-10623 Berlin
After natural ageing (NA), Al-Mg-Si alloys with various Mg and Si contents exhibit either positive or negative strength response during subsequent artificial ageing, which is caused by clusters formed during NA. Previous studies focused on cluster formation in Al-Mg-Si alloys by using Positron Annihilation Lifetime Spectroscopy (which is uniquely sensitive to vacancies) found that the entire evolution consists of at least 4 stages. However, the exact interpretation of the underlying microscopic processes is still under dispute. Therefore, in-situ positron lifetime experiments were carried out for pure Al-Mg and Al-Si binary alloys with solute concentrations ranging from 0.005 at.% to 1 at.% in order to clarify the behaviour of Mg/Si atoms on the clustering formation processes from a vacancy perspective. The results show that in general, a decrease in positron lifetime to a stable value after a certain period of NA for both alloying systems can be observed. Lifetimes of Al-Mg samples are significantly higher than in Al-Si alloys for equal solute content. In addition, these results are compared to the Differential Scanning Calorimetry results for getting a better understanding of the different clustering stages in Al-Mg-Si alloys.