73 Anton Smolej 1, * , Boštjan Markoli 1 , Aleš Nagode 1 , Damjan Klobčar 2 1 University of Ljubljana, Faculty of Natural Science and Engineering, Department of Materials and Metallurgy, Aškerčeva cesta 12, 1000 Ljubljana, Slovenia 2 University of Ljubljana, Faculty of Mechanical Engineering, Aškerčeva cesta 6, 1000 Ljubljana, Slovenia *Corresponding author. E-mail: anton_smolej@t-2.net Received: April 12, 2015 Accepted: July 2, 2015 Original scientifc paper Abstract The article describes the effect of varying minor scan- dium and zirconium quantities on the grain refinement of the as-cast alloys Al-Sc, Al-Sc-Zr, and Al-5Mg-Sc-Zr, as well as the distribution of either element in the phases formed during the solidification, homogenisation an- nealing, and ageing of these alloys. Scandium and zir- conium in the Al-Sc-Zr and Al-5Mg-Sc-Zr alloys are present in three metallographic formations: in the solid solution of the aluminium matrix, as primary particles Al 3 (Sc, Zr), and as dispersive precipitates. The prima- ry particles Al 3 (Sc, Zr), sized between 5 µm and 10 µm, act as crystallisation nuclei during the solidification of the alloys. As the EDS SEM analysis indicates, the primary particles are not homogeneous: the scandium and zirconium contents decrease from centre to edge. Another manifestation of scandium and zirconium in the Al-Sc-Zr and Al-5Mg-Sc-Zr alloys takes the form of secondary precipitates. These precipitates exist in the as-cast, homogenised, and aged alloys. Their sizes range from 5 nm to 60 nm in the as-cast alloys, and from 100 nm to 350 nm in the aged ones. The precip- itate number density decreases with the annealing of the alloys. Key words: aluminium alloys, scandium, zirconium, microstructure Izvleček Članek se osredinja na učinek različnih manjših koli- čin skandija in cirkonija na udrobnenje zrn v osnovnih zlitinah Al-Sc, Al-Sc-Zr in Al-5Mg-Sc-Zr in porazdelitev obeh elementov v fazah, ki nastanejo med strjevanjem, homogenizacijskim žarjenjem in staranjem teh zlitin. Skandij in cirkonij v zlitinah Al-Sc-Zr in Al-5Mg-Sc-Zr sta v treh metalografskih oblikah: v trdni raztopini alu- minijeve matrice, kot primarni delci Al 3 (Sc, Zr) in kot dispergirani izločki. Primarni delci Al 3 (Sc, Zr) z veliko- stjo od 5 µm do 10 µm so kristalizacijske kali med strje- vanjem zlitin. Kot je pokazala analiza EDS SEM, primar- ni delci niso homogeni; vsebnosti skandija in cirkonija se manjšata od sredine k robovom delcev. Drugi način pojavljanja skandija in cirkonija je v obliki sekundarnih izločkov. Izločki se nahajajo v ulitih, homogeniziranih in staranih zlitinah. Velikost izločkov je 5–60 nm v uli- tih in 100–350 nm v staranih stanjih zlitin. Gostota iz- ločkov se manjša z žarjenjem zlitin. Ključne besede: aluminijeve zlitine, skandij, cirkonij, mikrostruktura Influence of minor scandium and zirconium additions on the microstructure of Al and Al-5Mg alloy Vpliv manjših dodatkov skandija in cirkonija na mikrostrukturo Al in zlitine Al-5Mg