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Steinau an der Straße, Germany

Vlach M.,Charles University | Cizek J.,Charles University | Melikhova O.,Charles University | Stulikova I.,Charles University | And 5 more authors.
Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science | Year: 2015

Thermal effects on the precipitation stages in as-cast Al-0.70 at. pct Mn-0.15 at. pct Sc-0.05 at. pct Zr alloy were studied. The role of lattice defects was elucidated by positron annihilation spectroscopy (lifetime and coincidence Doppler broadening) enabling investigation of solutes clustering at the atomic scale. This technique has never been used in the Al-Sc- and/or Al-Zr-based alloys so far. Studies by positron annihilation were combined with resistometry, hardness measurements, and microstructure observations. Positrons trapped at defects are preferentially annihilated by Sc electrons. Lifetime of trapped positrons indicates that Sc atoms segregate at dislocations. Maximum fraction of positrons annihilated by Sc electrons occurring at 453 K (180 °C) suggests that clustering of Sc bound with vacancies takes place. It is followed by peak of this fraction at 573 K (300 °C). A rise of the contribution of trapped positrons annihilated by Zr electrons starting at 513 K (240 °C) and attaining maximum also at 573 K (300 °C) confirms that Zr participates in precipitation of the Al3Sc particles already at these temperatures. The pronounced hardening at 573 K (300 °C) has its nature in the precipitation of the Al3Sc particles with a Zr-rich shell. The contribution of trapped positrons annihilated by Mn electrons was found to be negligible. © 2015, The Minerals, Metals & Materials Society and ASM International. Source


Vlach M.,Charles University | Stulikova I.,Charles University | Smola B.,Charles University | Kekule T.,Charles University | And 5 more authors.
Kovove Materialy | Year: 2015

Microstructure, thermal, electrical and mechanical properties of the hot-extruded and hotrolled AlMnScZr alloys were studied. The electrical resistometry and microhardness together with differential scanning calorimetry measurements were compared with microstructure development observed by transmission electron microscopy, X-ray diffraction, and electron backscatter diffraction. Fine subgrain or grain structure developed and fine coherent Al3(Sc,Zr) particles precipitated during hot deformation and subsequent cooling. The distinct resistivity changes are mainly caused by precipitation of Mn-containing particles. The pronounced two-stage development of the Al6(Mn,Fe)-phase precipitation was observed. Nevertheless, the precipitation has a negligible effect on microhardness. The presence of the Mn-containing particles with a size of ∼ 50 nm inside subgrains or grains and ∼ 2 μm at subgrain or grain boundaries has a significant antirecrystallization effect. The combination of Mn, Sc and Zr additions to Al suppresses recrystallization during isothermal annealing at 550°C. Hot deformation has no effect on the apparent activation energy values of the Al3Sc-phase precipitation (Q = 109 kJ mol-1) and Al6Mn-phase precipitation (Q = 156 kJ mol-1). Source


Vlach M.,Charles University | Stulikova I.,Charles University | Smola B.,Charles University | Kekule T.,Charles University | And 7 more authors.
Materials Characterization | Year: 2013

The effects of cold-rolling on thermal, mechanical and electrical properties, microstructure and recrystallization behaviour of the AlScZr and AlMnScZr alloys prepared by powder metallurgy were studied. The powder was produced by atomising in argon with 1% oxygen and then consolidated by hot extrusion at 350 C. The electrical resistometry and microhardness together with differential scanning calorimetry measurements were compared with microstructure development observed by transmission and scanning electron microscopy, X-ray diffraction and electron backscatter diffraction. Fine (sub)grain structure developed and fine coherent Al3Sc and/or Al3(Sc,Zr) particles precipitated during extrusion at 350 C in the alloys studied. Additional precipitation of the Al3Sc and/or Al3(Sc,Zr) particles and/or their coarsening was slightly facilitated by the previous cold rolling. The presence of Sc,Zr-containing particles has a significant antirecrystallization effect that prevents recrystallization at temperatures minimally up to 420 C. The precipitation of the Al6Mn- and/or Al 6(Mn,Fe) particles of a size ~ 1.0 μm at subgrain boundaries has also an essential antirecrystallization effect and totally suppresses recrystallization during 32 h long annealing at 550 C. The texture development of the alloys seems to be affected by high solid solution strengthening by Mn. The precipitation of the Mn-containing alloy is highly enhanced by a cold rolling. The apparent activation energy of the Al3Sc particles formation and/or coarsening and that of the Al6Mn and/or Al 6(Mn,Fe) particle precipitation in the powder and in the compacted alloys were determined. The cold deformation has no effect on the apparent activation energy values of the Al3Sc-phase and the Al 6Mn-phase precipitation. © 2013 Elsevier Inc. Source


Vlach M.,Charles University | Stulikova I.,Charles University | Smola B.,Charles University | Kudrnova H.,Charles University | And 5 more authors.
METAL 2013 - 22nd International Conference on Metallurgy and Materials, Conference Proceedings | Year: 2013

The conference paper reports results of a study aimed at understanding precipitation processes of the binary Al-Mn and quaternary Al-Mn-Sc-Zr alloy. The alloys were investigated in the mould-cast state and cold-rolled state. The alloys were studied during step-by-step quasilinear annealing from 200 °C up to 600 °C with heating rate 100 K/h followed by subsequent isothermal annealing at 600 °C/4 h. The effect of the pseudo-homogenization heat treatment (610 °C/18 h) on mechanical properties of the alloys during isothermal annealing at 300, 400 and 500 °C was also investigated. Precipitation reactions were studied by electrical resistometry and (micro) hardness measurements. The microstructure development was investigated by transmission, scanning electron microscopy and electron diffraction examinations. The hardening effect is due to fine, coherent, uniformly distributed Al3Sc and/or Al3(Sc,Zr) particles. The distinct changes in resistivity of the cold-rolled alloys at temperature above ∼ 300 °C are mainly caused by precipitation of Mn-containing particles. Precipitation of these particles has an insignificant effect on microhardness. © 2013 TANGER Ltd., Ostrava. Source


Vlach M.,Charles University | Stulikova I.,Charles University | Smola B.,Charles University | Cisarova H.,Charles University | And 4 more authors.
METAL 2012 - Conference Proceedings, 21st International Conference on Metallurgy and Materials | Year: 2012

The paper reports results of a study aimed at understanding the precipitation processes of quaternary coldrolled AlMnScZr alloys during isothermal annealing at 300 °C and 400 °C and during annealing with constant heating rate from room temperature up to 570 °C. The resistivity, conductivity and microhardness behaviour was compared to microstructure development. The changes in resistivity and conductivity of the alloys at temperature above ∼ 360 °C are mainly caused by precipitation of the Al6Mn particles. This precipitation is dependent on deformation degree. The deformation of the alloys shifts the Al6Mn-phase precipitation to lower temperatures compared to the mould-cast AlMnScZr alloy. The activation energy for Al3Sc- and Al6Mn-phase precipitation was also determined. The obtained results agree with conclusions on the cold-deformed AlMnScZr alloys studied in our previous works. Source

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