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.
Based on high-speed studies of the dynamics of Portevin-Le Chatelier ambryo bands with a temporal resolution of up to 20 and a spatial resolution of up to 10 , their classification is proposed, which includes four types of bands depending on the nature of interaction with other bands and the sample surface (using the example of a polycrystalline aluminum-magnesium alloy) . It has been found that all types of ambryo bands demonstrate nonlinear dynamics with a sharp acceleration of the band tip and the growth rate of its volume at the final stage before reaching the sample surface. A phenomenological model of the nonlinear growth of the ambryo band is proposed, which explains the exponential self-acceleration stage observed experimentally. The sharp absorption of acoustic noise at the stage of accelerated band growth is discussed.
На основе анализа данных высокоскоростной видеосъемки распространяющихся деформационных полос в алюминиево-магниевом сплаве установлено, что подвижная полоса деформации содержит избыток дислокаций одного механического знака, а основным механизмом распространения фронта локализованной пластической деформации вдоль оси образца является эстафетная передача скольжения в антипараллельном направлении для релаксации изгибающего момента, создаваемого первичной полосой деформации. Показано, что "мгновенная" скорость пластической деформации в течение ~1 ms в растущей полосе достигает значения ~103 s-1, сравнимого со скоростью деформации при ударных испытаниях. Ключевые слова: прерывистая деформация, полосообразование, дислокации, механический заряд, алюминиево-магниевый сплав.
The effect of local corrosion on the dynamics of macrolocalized deformation bands and the destruction of an AlMg6 aluminum-magnesium alloy was investigated by high-speed video filming of the deformable sample surface. It has been established that a corrosion stain caused by a local effect of sodium hydroxide on the surface of the alloy is an attractor of deformation bands, the interaction of which leads to premature failure and reduction of the ductility of the alloy.
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