Boštjan Markoli, et al., Influence of cooling rate and alloying elements on the microstructure… Contemporary Materials, V−1 (2014) Page 30 of 36 Original scientific papers UDK 669.715'3'74 doi: 10.7251/COMEN1401030M INFLUENCE OF COOLING RATE AND ALLOYING ELEMENTS ON THE MICROSTRUCTURE OF THE Al-Mn-BASED ALLOY Boštjan Markoli 1,* , Kemal Delijić 2 , Neva Štrekelj 1 , Iztok Naglič 1 1 Faculty of Natural Sciences and Engineering, University of Ljubljana, Aškerčeva 12, Ljubljana, Slovenia 2 Faculty of Metallurgy and Technology, University of Montenegro, Cetinjski put bb, Podgorica, Montenegro Abstract: Aluminum-based alloys have been used extensively for the past five dec- ades primarily due to their good strength vs. specific weight ratio. Numerous methods and techniques have been devised to further improve mechanical properties of these alloys as they are often used in the transport applications. Influence of the cooling rate and chemical composition on the constitution of Al-Mn-based alloy has been investigated. Elements such as B, Be, C, Ca, Cu, Fe, Mg, Si, Sr and Ti have been introduced to Al-Mn alloys in order to study their influence. Changes in cooling rates during casting using permanent copper molds with different sized troughs have also been monitored. Combined influence of changes in chemical composition and cooling rates was followed using LOM, SEM, EDS, DAS measurement and mathematic modeling. It has been established that Al-Mn-based al- loys form a lot of different phases during synthesis and solidification, mostly crystalline in- termetallics, but also in some cases quasicrystalline (QC) ones, especially when cooling rates exceed 500 Ks -1 . QCs are currently also considered as an alternative for reinforcement of Al-Mn-based alloys. It was found that in the case of alloy system Al-Mn-Cu-Be and cooling rates between 500 and 1350 Ks -1 the preferred phase formed was an icosahedral QC phase or iQC. Icosahedral QC phase formed as the primary phase and in some cases also in the form of the quasicrystalline eutectic (α Al + iQC). Additions of B, C, Ca, Ti and Sr have not proven to be effective in promoting formation of quasicrystals in cast Al-Mn alloys whilst Fe, Cu, Mg and Si proved to be highly efficient. Keywords: Al-Mn alloys, cooling rate, chemical composition, quasicrystals. 1. INTRODUCTION Lightweight and high-strength alloys which have a high strength and density ratio are desirable since such properties enable reduction of weight of constructions made from such materials. Reduction of weight in transportation for example is one of the main motives as it allows reduction of energy con- sumption, of harmful emissions as well as improved performance. Aluminum alloys have been used in transportation industry for at least half a century. Such alloys should, besides desired properties, also allow for large scale production which ought to be as simple as possible. The strength of aluminum alloys can be increased via various mechanisms among which e.g. strengthening by grain size reduction, solid-solution strengthening, precipitation and strain hardening. Quasicrystalline state is the third state of matter and as such has special physical and metal- lurgical properties [1,2]. Quasicrystals (QCs) are deformable but still relatively hard materials and could as such serve as a reinforcing phase of in-situ produced aluminum-based composite materials [3- 6]. Such primary formed QC phases for instance can deform together with aluminum matrix while they still harden the alloy due to higher hardness in com- parison to aluminum matrix. QCs were found in numerous aluminum- based alloy systems as equilibrium or metastable phases [7]. In an Al-Mn system, where they were first reported, primary icosahedral QCs (iQCs) were formed only at high cooling rates which are not achievable by existing conventional large scale cast- ing technologies [8]. Adding elements like beryllium enabled the formation of iQCs also at moderate cooling rates (around 500 Ks -1 ) which can be achieved using conventional casting technologies [9- 20]. Recent results indicate that primary iQCs can * Corresponding author: bostjan.markoli@omm.ntf.uni-lj.si