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The prospects for the use of scandium and zirconium for alloying aluminum alloys with the aim of increasing their high-temperature strength make it necessary to investigate the interaction between aluminum and these metals. The present work is devoted to a study of phase equilibria in the AI-Sc-Zr system at 500~ by methods of physico-chemical analysis and of the effect of a third component on the principal characteristics of binary intermetallic compounds.Phase equilibrium in the AI-Sc-Zr system at 500-600~ in the aluminum-rich region has been studied in [1 -6]. It has been established that the ScAI 3 and ZrAI 3 phases are in equilibrium with AI. The aluminum-rich region does not contain intermetallic compounds, but it has been shown in [6] that up to 15% Zr 2 can dissolve in the ScAI 3 phase at 550~ and up to 2.5% Sc can dissolve in the ScAI 3 phase. The presence of such phases with a variable composition can exert a considerable effect on softening processes in the alloys, 9o vo~ which makes it necessary to study phase equilibria in the A1 -/// Sc -Zr system in greater detail. In the present work we plot-8 0n.AI, at.% 1 ScAI3"~ ' ted the time-temperature section of the phase diagram of the /, 70A~:F_.j AI -Sc -Zr system in the entire range of aluminum concenScAl~ trations at 500~ Z-------)~The alloys for the investigation were melted in an electric ScA!/ \ .,.r arc furnace in an argon atmosphere. The specimens were sub5o,~ jected to a homogenizing annealing for 110 h at 500-750~ 4o~ (depending on the composition of the alloy). Then the firing Sc2AI~/" X /_X..~--,G~. temperature was decreased to 500~ The firing at 500~ was 30(~~ ---) conducted for 400 h. 2o2o / \zr]A~f~ •/The charge was prepared from aluminum of grade A99, j'\ /\ /\ /~. scandium of grade SkM, and zirconium iodide. The compositions of the studied alloys are presented in Fig. 1. The compo-, .... sition of the alloys was controlled by emission spectral analySc 9o 8o 70 6o sis using an ISP-30 spectrometer. The analytic pairs of Sc-AI lines (at wavelengths k = 269.9 and 266.0 nm, respectively) and Zr-AI lines (at k = 339.2 and 305.0 rtm, respectively) were used for the spectral analysis of the contents of Sc and Zr.I Moscow State University, Moscow, Russia.2 Here and below we use the element atomic fraction.The microstructural analysis was conducted using a Neophot-2 metallographic microscope (at a 200-fold magnification). The specimens were etched in a 10% solution of HF and in a mixture of 5% solutions ofHF, HCI, and HNO 3. The x-ray phase analysis was conducted by a powder method in 3 ) ScAI2 + ZrAI 2 + Zr2AI3; 4 ) ScAI 2 + Zr2AI 3 + ZrAI; 5 ) ScAI + ZrAI + Zr4AI3; 6 ) Zr3AI 2 + 13 + Zr4AI3; 13) a continuous series of solid solutions between Sc2AI and Zr2AI; ct) a continuous series of solid solutions between ct-SC and a-Zr.

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