A.V. Dobromyslov (1), J.Dutkiewicz (2), G.V. Dolgikh (1), T.L. Trenogina (1), and A.N. Martem'yanov (1)
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(1) Institute of Metal Physics, Ural Division of Russian Academy of Sciences
(2) Institute of Metallurgy and Materials Science Polish Academy of Sciences
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High pressure can strongly influence upon the decomposition processes of supersaturated solid solution. However, there is only limited number of investigations in which this problem is considered. Therefore, in the present study, the aging behaviour of the Al(4 wt.% Cu alloy under high pressure has been investigated. Aging treatments under high hydrostatic pressure were carried out in the container of the M20 device. The specimens used for aging under hydrostatic pressure of 12 kb had the shape of plates (10x10x40mm3). Aging treatments under quasihydrostatic pressure of 80 kb were carried out in a catlinite toroidal container placed between anvils of the appropriate profile. The pressure-transmitting medium was sodium chloride. A manometer, calibrated on the basis of the phase transitions in bismuth, was used to measure the pressure. The specimens were heated by transmission of an electrical current through a graphite bush in the high-pressure cell after creation of the pressure. The precipitation hardening in the Al(4 wt.% Cu alloy has been achieved in two steps: first the solution treatment (1 hour at 540(C) with water quenching has been performed and, in the next step, the specimens have been subjected to aging under hydrostatic pressure of 12 kb (24 hours at 150(C; 3 hour at 270(C) or quasihydrostatic pressure of 80 kb (5 hours at 200(C; 1 hour at 250(C; 0,5 hour at 300(C; 5 hours at 300(C). Microstructure investigations were performed in a JEM-200C transmission electron microscope. High pressure-aging experiments show that both hydrostatic and quasihydrostatic pressure suppress strongly the decomposition processes in the quenched Al(4 wt.% Cu alloy. After aging at 150(C for 24 h (pressure of 1 kb) the precipitate has the (( structure. High pressure of 12 kb suppress the formation of the ((-phase completely. Diffuse streaks observing on diffraction pattern point to presence of the GP-1 zones. When the aging temperatures is increased (240 and 270(C) formation of the ((-precipitates take place during aging under hydrostatic pressure. In contrast to them quasihydrostatic pressure of 80 kb suppressed formation metastable precipitates in the Al(4 wt.% Cu alloy. Additional aging of alloy beforehand subjected high pressure-aging treatment leads the appearance of metastable precipitates.

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