Влияние температуры равноканального углового прессования на формирование мелкозернистой структуры в сплаве Al-3 %Cu

Abstract

Тhe effect of the temperature of equal channel angular pressing (ECAP) on the microstructural changes in a model alloy Al-3 %Cu was investigated. ECAP of the as- homogenized and preliminary overaged alloy with an initial grain size ranging from 200 to 400 μm was performed by route A up to effective strains 8 –12 under isothermal conditions in the temperature range 150 – 400°C (0.45 – 0.75 Tm). ECAP at 150°C led to the significant refinement of the grain structure of the alloy. New fine grains were predominantly formed due to fragmentation of the original grains by the development of mutually intersected deformation- / microshear bands, which initially had the medium-angle misorientations (from 5 to 15°). The number of bands, as well as their boundary misorientations, gradually increased during deformation, leading to the development of crystallites surrounded by high-angle boundaries in accordance with the mechanism of continuous dynamic recrystallization. After 8 ECAP passes, a partially recrystallized structure was obtained in the material, containing regions of (ultra)fine grains with an average size of about 1.2 μm and arrays of the fragmented structure. The average misorientation angle in such the structure was as high as 23.2° and the fraction of high-angle boundaries was about 50 %. Precipitates of Θ (Al2Cu)-phase present in the alloy hindered the dynamic and static recovery and grain growth at the elevated ECAP temperature, and so stabilized the forming grain structure. The increase of the ECAP temperature to 400°C postponed the formation of the fine-grain structure to higher strains and resulted in increase in the average size of new grains to 15 μm, as well as decreased the fraction of high-angle boundaries to 30 % and the average misorientation angle of intercrystallite boundaries to 16.2°. The main reasons for the suppression of the fine-grain structure formation with increasing the ECAP temperature were the occurrence of a more uniform deformation in the earlier stages of processing and the gradual dissolution of the Θ-phase that stabilized the alloy structure.