Contents lists available at ScienceDirect Materials Characterization journal homepage: www.elsevier.com/locate/matchar Increased structural stability in twin-roll cast AZ31 magnesium alloy processed by equal channel angular pressing P. Minárik a, ⁎ , M. Zimina b , J. Čížek c , J. Stráska a , T. Krajňák a,d , M. Cieslar a , T. Vlasák c , J. Bohlen e , G. Kurz e , D. Letzig e a Department of Physics of Materials, Charles University, Prague, Czech Republic b Research Center Rez, Ltd., Husinec-Řež, Czech Republic c Department of Low Temperature Physics, Charles University, Prague, Czech Republic d Institute of Physics, Slovak Academy of Sciences, Dúbravská cesta 9, 845 11 Bratislava, Slovakia e Magnesium Innovation Centre (MagIC) Helmholtz-Zentrum Geesthacht, Geesthacht, Germany ARTICLE INFO Keywords: Magnesium Twin-roll casting ECAP Thermal stability Microstructure ABSTRACT The present paper reports an effect of ECAP on the microstructure of the AZ31 magnesium alloy prepared in two conditions: conventionally cast and twin-roll cast. Subsequently, the thermal stability of fine-grained conditions was investigated with a special regard to microhardness, grain structure and dislocation density changes. Similar processing conditions of ECAP resulted in achieving similar average grain size for both initial conditions re- gardless differences in the initial microstructure. The only difference in the microstructure of a fine-grained condition was a distribution of β-Al 12 Mg 17 secondary phase particles. Isochronal annealing in the temperature range 160–500 °C showed differences in the response of individual fine-grained samples to the temperature increase. It was proven that these differences primarily originated from the different distribution of secondary phase particles, which significantly affected static recovery and grain growth. Consequently, the thermal sta- bility of fine-grained structure was much better in twin-roll cast samples in the temperature range 220–340 °C. Exceeding 340 °C, accelerated dissolution of β-Al 12 Mg 17 phase resulted in a similar evolution of all studied parameters showing that distribution of secondary phase particles is a crucial parameter of thermal stability of fine-grained AZ31 magnesium alloy. 1. Introduction Magnesium alloys can be used for a wide variety of construction applications due to the low weight and several unique properties, such as high specific strength and stiffness, high dimensional stability and good thermal and electrical conductivities [1,2]. Automotive, aero- space, sports and computer industries, where the weight reduction is critical [3–5], are primary areas of magnesium alloy utilizations. Nowadays, the most used commercial alloys are based mainly on Mg- Al-Zn (AZ) system, particularly AZ91, AZ61 and AZ31. The latter has the lowest pitting susceptibility [6] and could be also easily recycled using e.g. hot extrusion [7]. On the other hand, AZ91 is still the most widely used die casting alloy with a good corrosion resistance, good die castability and high strength [6,8,9]. However, cast AZ-type alloys cannot be used at temperatures higher than 120 °C due to their poor creep resistance [8]. Selection of casting and further processing and/or thermomechanical treatment is crucial for the production of the material with desired microstructure and physical properties. Twin-roll casting (TRC) is a new generation of continuous casting techniques, which allows to obtain feedstock in the form of a plate al- ready with a relatively fine-grained microstructure (if measures for cast materials are applied). Melt is fed through a nozzle into the gap be- tween two rotating water-cooled rolls and then it cools down and so- lidifies between the rolls. The final product is a 4–6 mm thin sheet with a high-quality surface. This is provided particularly by a high cooling rate of the melt; therefore, non-intermittent withdrawal regime is reached, which leads to the absence of cracks in the surface layer [10]. In contrast to conventionally cast alloys, TRC strips have a hetero- geneous structure but much finer grains, usually 50–100 μm in diameter [11,12]. Consequently, enhanced mechanical properties compared to the conventionally cast counterparts are usually achieved. The other beneficial attribute of the TRC process is incorporating casting and hot rolling into one step; therefore, this process is more efficient. TRC has been successfully applied to aluminum [12,13], steels [14,15] and https://doi.org/10.1016/j.matchar.2019.05.006 Received 7 February 2019; Received in revised form 4 April 2019; Accepted 4 May 2019 ⁎ Corresponding author. E-mail address: peter.minarik@mff.cuni.cz (P. Minárik). Materials Characterization 153 (2019) 199–207 Available online 06 May 2019 1044-5803/ © 2019 Elsevier Inc. All rights reserved. T