Microstructure stability of ultra-fine grained magnesium alloy AZ31 processed by extrusion and equal-channel angular pressing (EX–ECAP)

Continuous measurement of m-parameter for Hart analysis of superplastic behaviour of ultra-fine grained AZ31 Mg alloy

“…The decrease of m-parameter for 250°C is therefore probably caused by disappearing of fast diffusion paths possibly due to recovery of dislocation walls reducing the Cobble creep and also due to grain growth, which limits superplastic behaviour according to classical Ashby-Verrall model [17]. Limited work hardening at 250°C is also attributed to recovery processes, which occur during static annealing 250°C [8,18]. The grain growth during the tensile test is a topic for further investigation, but the grain growth might be even faster under dynamic conditions [11].…”

“…The grain growth during the tensile test is a topic for further investigation, but the grain growth might be even faster under dynamic conditions [11]. Possible effect of annealing twins observed in [8,18] for annealing temperature of 250°C remains unclear. On the other hand, during annealing at 175°C and 200°C limited decrease of dislocation density was observed [8] and the m-parameter decreases more slowly.…”

“…The superplastic behaviour is related to microstructure stability at increased temperature, which was investigated in detail in our previous study [8]. The effect of forming temperature on superplastic behaviour and strain hardening is discussed using Hart methodology [9] performed for UFG Mg alloy by Figueiredo and Langdon [3].…”

Microstructural changes of ECAP-processed magnesium alloy AZ91 during cyclic loading at different stress-amplitude levels

“…4,5 The materials processed via ECAP (or generally with any SPD method) exhibit a certain microstructural instability caused by high inner energy and unstable (grain) boundaries. The microstructural stability loss can occur during a thermal exposition 6,7 or mechanical loading (predominantly fatigue loading). 8,9 The instability can be manifested as grain coarsening connected with a decrease in the mechanical properties, which can be lower than the properties of an unprocessed, virgin material.…”

Анализ Изменения Диффузионных Свойств Неравновесных Границ Зерен При Рекристаллизации И Сверхпластической Деформации Субмикрокристаллических Металлов И Сплавов

“…Тем не менее анализ экспериментальных данных по исследованию процессов миграции границ зерен при отжиге СМК-сплавов [4][5][6][7][8][9], а также процессов сверхпластической деформации СМК-металлов при повышенных температурах [10,11] показывает, что диффузионные свойства границ зерен в некоторых случаях весьма значительно отличаются от равновесных. Следует также отметить ряд работ, в которых наблюдалась немонотонная зависимость ко-эффициента зернограничной диффузии D b и энергии активации Q b от температуры нагрева [4,6,8,[12][13][14].…”