A study by resistivity measurements at 20ยฐC has been carried out on the effects of small magnesium concentrations (to a magnesium of 1.08 per cent at. fr. Mg) on the annealing out of vacancies frozen-in by quenching sluminium wires (quenching medium: brine at 2ยฐC). The following results are observed:
(1) a concentration as small as about 0.13 per cent at. fr. of Mg atoms is sufficient nearly to suppress the annealing out of vacancies which is observed in pure aluminium at room temperature; (2) in the meantime we have an increase of resistivity of the sample which is sensitive to the quenching speed; (3) this increase is annealed out in isochronal annealing in the range SO-120ยฐC. These facts are easily interpreted if we assume, in agreement with a point of view advanced recently by Perryman in the case of the examination of other properties of Al-Mg alloys, that magnesium atoms in aluminium are able to trap vacancies at room temperature and that only at about 80-120ยฐC vacancies can free themselves from traps. A preliminary study of the isothermal annealing out of vacancies in the presence of magnesium has shown that the phenomenon is complex and not well understood. Finally, some additional experiments on the isochronal recovery of resistivity of cold-worked Al-Mg alloys have shown that in the same range in which it is possible to observe the recovery after quenching, a larger recovery, the greater the magnesium content, is observed. This result is in agreement with the view of generation of vacancies by cold-working. INTERACTION ENTRE LACUNES ET ATOMES DE MAGNESIUM DISSOUS DANS L'ALUMINIUM