Optimization of aging regimes of alloys in the Al−Mg system for stabilizing the structure and mechanical properties

Abstract

The previous study of the authors has resulted in the development of an A1-10% Mg composition alloyed additionally by zinc, manganese, antimony, and zirconium. The alloy was to be cast into sand molds and had Or = 380 --400 N/mm 2, o02 = 240 -260 N/mm 2, and 8 = 10 -12%. The main difficulty in the development and use of the given alloy consisted in attaining stable properties in the operating process. The present paper is devoted to this problem.It is known that alloys based on the A1 -Mg system with a magnesium content exceeding 8% are susceptible to natural aging after quenching by a regime that causes maximum sanration of the solid solution (for attaining high mechanical properties). After natural aging the strength parameters increase insubstantially, but the elongation decreases considerably. In combination with the relatively low yield limit (%.2 ~ 0.5 %) this can cause embrittlement of the alloy and failure of the castings.In order to eliminate the negative effect of natural aging, we have developed a heat-treatment regime for an experimental alloy, which includes quenching in boiling water after a hold at 435~ for 20 h and aging at 80-100~ for 35-45 h [1].The aim of the present work consists in refining the regime in order to guarantee the specified level of properties and their stability in the process of subsequent operation and to save energy.A preliminary study has shown that the temperaturetime regime of quenching mentioned above is optimum because it provides a full dissolution of magnesium and eliminates burning of the alloy, which is an irreparable defect in heat treatment.We used the method of mathematical design and tested a two-stage aging regime with variation of the variable within the following ranges: