Vacancy-solute interaction in magnesium alloy WE54 during artificial ageing: a positron annihilation spectroscopy study

摘要

The vacancy-solute interaction during artificial ageing at 250℃ was studied in the commercial alloy WE54 by coincidence Doppler broadening of the positron annihilation radiation. The results show that in the initial state of ageing positron trapping is weak. Under these conditions, the faint signal comes predominantly from small Zr particles, with minor contributions from vacancy-Nd complexes. Positron trapping increases concomitantly with the formation of the β'- and β{sub}1-phases at the onset of precipitation hardening, and becomes very intense at later ageing stages when the β{sub}1-phase is formed. The chemical composition in contact with open-volume defects changes after 4 h of ageing with a progressive enrichment in Mg, concomitant with a hardness increase. There is evidence for a prevalence of Nd over Y up to 24 h of ageing and then a prevalence of Y over Nd for 96 h (Y/Nd ≈ 3) when the β-phase is dominant.