Mariia Zimina

The influence of ECAP on microstructure evolution of aluminium alloys during in-situ heating in TEM

Abstract Twin-roll casting of aluminium alloys produces sheets with high solid-solution supersaturation. During high tempe-rature processing the solid solution decomposes and cubic α-Al(Mn, Fe)Si precipitates form. Processing by equal channel angular pressing introduces new grain boundaries into the material and shifts the precipitation to lower temperatures. In-situ annealing in a transmission electron microscope enables dynamic observation of recovery, precipitation, particle dissolution and grain growth. However, most of the processes observed by in-situ transmission electron microscopy occur at temperatures that are lower than temperatures estimated from specimens annealed conventionally in a furnace.

Effect of pre-annealing on microstructure evolution of TRC AA3003 aluminum alloy subjected to ECAP

Abstract An AA3003 aluminum alloy prepared by twin-roll casting was modified by a small amount of zirconium. Annealing at 450 °C led to precipitation of coherent Al 3 Zr phase and a simultaneous co-precipitation of Mn-rich α -Al(Mn, Fe)Si phase. Severe plastic deformation by equal channel angular pressing resulted in the grain refinement and increase of microhardness. Observation by electron back-scatter diffraction and in-situ transmission electron microscopy revealed influence of pre-annealing on microstructure changes during post-deformation heat treatment. Dislocation recovery and precipitation of α -Al(Mn, Fe)Si particles preceded recrystallization at 450 °C in material which was not annealed before deformation. The pre-deformation annealing enabled dynamic recovery during deformation as it depleted the solid solution from Mn atoms. Recrystallization was enhanced by Al 3 Zr precipitates.

The study of microstructure and mechanical properties of twin-roll cast AZ31 magnesium alloy after constrained groove pressing

Microstructure investigation and microhardness mapping were done on the material with ultra-fine grained structure prepared by constrained groove pressing of twin-roll cast AZ31 magnesium strips. The microstructure observations showed significant drop of the grain size from 200 gm to 20 gm after constrained groove pressing. Moreover, the heterogeneities in the microhardness along the cross-section observed in the as-cast strip were replaced by the bands of different microhardness in the constrained groove pressed material. It is shown that the constrained groove pressing technique is a good tool for the grain refinement of magnesium alloys.

Microstructure Evolution of AA3003 Aluminum Alloys Enhanced by Zirconium Addition Studied by Electron Microscopy

Zirconium added to aluminium alloys may under suitable conditions form metastable cubic precipitates Al3Zr, which pin moving grain boundaries and thus shift recrystallization to higher temperatures. Twin-roll cast AA3003 aluminium alloy cold-rolled to 5 and 1 mm was subjected to several annealing steps in order to find ideal conditions for precipitation of Al3Zr phase. Mechanical properties were monitored by microhardness measurement and microstructure was observed by light microscope and transmission electron microscope. Annealing to 450 °C with slow heating rate has been used to produce Al3Zr precipitates. This heat treatment also influenced presence of other phases like cubic α-Al(Mn,Fe)Si. The main mechanisms influencing microhardness were hardening by Al3Zr precipitates, softening by recovery and recrystallization and depletion of the solid solution from the major alloying elements.

Properties and microstructure of twin-roll cast Al-Mg alloy containing Sc and Zr

The influence of Sc and Zr on microhardness and microstructure of twin-roll cast Al-Mg alloy was studied. A significant effect of Sc and Zr on hardening of the material after annealing in a temperature interval between 250 °C and 400 °C was confirmed. Maximal hardness was obtained after annealing above 300 °C due to a precipitation of a fine dispersion of Sc and Zr containing precipitates. An exposure of the annealed material to higher temperatures suppresses the influence of these particles due to changes of the strengthening effect of precipitates. However, a partially positive role of remaining precipitates hindering recrystallization persists even up to 550 °C.

Deformation of Open‐Cell Microcellular Pure Aluminum Investigated by the Acoustic Emission Technique

Acoustic Emission (AE) is used to characterize the plastic deformation of open-cell pure aluminum foams produced by salt replication. Measurements were performed on samples with cells 25, 75 or 400 μm in average diameter, all with a relative density near 24%. AE signals were measured during compression tests conducted with a constant cross-head speed. Deformation is uniform along the porous metal samples. Recorded AE accompanying plastic deformation of the cellular structure exhibits intermittent behaviour, with the probabilities of AE event energies distributed according to a power-law similar to those previously found in many different materials. The present study thus confirms the universal scale-free character of global plastic deformation dynamics and extends the observation to pure aluminum.