Формирование полос макролокализованной деформации в условиях прерывистой ползучести исследовали методами акустической эмиссии (АЭ) и высокоскоростной видеосъемки. Установлено, что наиболее быстрые стадии формирования полосы деформации, связанные с ее выходом на поверхность и последующим ускоренным расширением, сопровождаются генерированием всплеска сигнала АЭ в полосе ~0.05-1 MHz. Скрытые корреляции в сложной структуре акустического всплеска исследовали методами статистического и фрактального анализа. Установлена связь между огибающей акустического всплеска и скоростью изменения силового отклика, вызванного формированием одиночной полосы деформации. Ключевые слова: прерывистая деформация, ползучесть, акустическая эмиссия, полоса деформации, фрактальная структура, алюминий-магниевый сплав.
Spatio-temporal structures of Portevin-Le Chatelier deformation bands at the pre-failure stage, necking and destruction of an aluminum-magnesium alloy, deformable in an aqueous medium, were investigated by a complex of in situ methods, including high-speed video of the surface and an electrochemical emission method. The latter is based on measuring and analyzing jumps in the electrode potential of a deformable metal under the conditions of the manifestation of intermittent deformation. It is established that discrete signals of electrochemical emission in the frequency band of 10 Hz - 10 kHz contain information on the number of deformation bands, the moments of nucleation and stages of their growth, the statistical temporal structure of the bands, etc. A characteristic series of signals at the pre-failure stage is revealed − an electrochemical precursor neck formation and specimen fracture. The connection between the generation of electrochemical emission signals and the localization of plastic deformation and the destruction of an oxide film on an aluminum alloy surface in contact with an aqueous medium is discussed.
The effect of surface processing by laser IR radiation on strength and Portevin–Le Chatelier serrated deformation of AlMg6 aluminum–magnesium alloy is experimentally studied. Laser processing consists in local “shots” on the surface at the nodes of a square grid in the gauge part of a flat sample. The conditions under which such laser processing causes an increase in the surface microhardness, ultimate tensile strength, and the critical strain of the first stress drop in the stress–strain curve; decreases the probability of deformation band formation; suppresses necking at the prefracture stage; and changes the main crack morphology. The possible mechanism of the effect of laser processing on band formation, serrated deformation, and alloy strength are discussed.
It has been established that the Portevin–Le Chatelier effect in the AlMg6 aluminum–magnesium alloy deformed in an aqueous medium is accompanied by an intermittent electrochemical response, such as the negative jumps of the electrode potential of the sample, which occur simultaneously with the jumps of the mechanical stress on the deformation curve. Statistical and fractal analyses of the stepwise component of the electrode potential indicate the presence of long-term correlations in the structure of the electrochemical response, which are typical for the state of self-organized criticality. A possible mechanism of the appearance of jumps of the electrode potential, which is associated with the dynamics of deformation bands, is discussed.
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