Effect of quenching regimes on the structure and properties of an alloy from the Al−Mg system

Abstract

All industrial alloys of the AI-Mg system correspond to the region of the a-solid solution of the phase diagram. Domestic alloys AL8 and AL27-1 and foreign alloys 520 (USA) and LM-10 (Great Britain) with a high magnesium content (9 -11%) have high mechanical properties after quenching. However, they possess a high sensitivity to natural aging under conditions of long-term operation or storing, which causes their embrittlement. The aim of the present work consists in developing an AI-Mg-base composition quenched and aged artificially that will possesses a high strength (err = 380-400 N/ram 2) and will not change in operation at a temperature of at most 100~We chose alloy AL27-1, which is the strongest domestic alloy of the AI -Mg system for our study. In order to choose an optimum composition we used the method of experiment design with a Schaeffer simplex lattice of the third order. Figure I presents the dependences of the mechanical properties of quenched alloy AL27-1 (10.2% Mg, 0.08% Ti, 0.11% Zr, < 0.05% Fe, < 0.l% Si, the remainder AI) on the regimes of artificial aging. After quenching from 435 + 5~ (20h) in water with G=100~ the alloy has G = 375 N/mm 2, 8 = 22.0%. An analysis of the obtained results has shown that artificial aging in the studied range of tema t, ~ peratures and hold times does not cause an additional oo ~xyg~ strengthening of the quenched alloy. An increase in the hold temperature and time for every temperature of artificial aging 2 ~ ~ N/ram2 decreases the strength and the elongation of the quenched alloy, i so~/ ~a~ In accordance with triple-phase diagrams we introduced /%N2\ additional elements into the binary AI-Mg alloy in combi-100.,/ ]G.~-----~-N-..,~ nations and amounts that would prevent the formation of an embrittling !3-hase, namely, 6 -16% Mg, 0 -5% Zn (in order so. to increase the strength), O-2% Mn (in order to decelerate 6 27 ~, h 48 the diffusion processes of the decomposition of the solid sot, ~ lution and increase its stability), O-2% Sb (in order to inoo "~ a, crease the stability of the solid solution, improve the corro2oo sion resistance and decrease the crack formation), and 0-~ 0.05% Zr (in order to disintegrate the structure). After the exis0~-~14 x periments and a mathematical analysis of the results we have chosen an optimum composition for the alloy.Ioor 20 ~--~\ We conducted a comparative metallographic and differ-/ ential thermal (DTA) analysis of alloy AL27-1 and an experi-50.L 6 2'7 48

Optimization of aging regimes of alloys in the Al−Mg system for stabilizing the structure and 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: …”