The effect of annealing on properties of continuously casted Cu - Al alloy

U ovom radu je prikazan utjecaj toplinske obrade (ţarenja na 900 °C u trajanju 15 i 30 minuta) na mikrostrukturu, mikrotvrdoću i mehanička svojstva Cu - 9,1Al legure. Navedena legura predstavlja predleguru za dobivanje Cu - Al - Mn - Zn legure s efektom prisjetljivosti oblika. Najprije je proizveden ingot dimenzija Ø 110 x 180 mm koji je pretaljen te kontinuirano lijevan u oblik cilindrične šipke promjera 8 mm. EDS analiza kemijskog sastava je potvrdila da je lijevanje Cu - 9,1Al legure uspješno provedeno (proizvedena je legura homogenog sastava). Optičkom i pretraţnom elektronskom mikroskopijom primijećena je prisutnost dvofazne α + β mikrostrukture koja se zadrţava i nakon toplinske obrade iako dolazi do odreĎene mjestimične promjene morfologije α - faze. DSC analizom je primijećena jedna endotermna promjena toplinskog toka prilikom zagrijavanja koja vjerojatno predstavlja α→β transformaciju i jedna egzotermna promjena toplinskog toka prilikom hlaĎenja koja vjerojatno predstavlja β→α transformaciju. Uočene razlike mikrotvrdoće i vlačne čvrstoće su neznatne dok istezanje opada prilikom duţeg izlaganja ţarenju. Promjene u iznosu kontrakcije podudaraju se s promjenom vrijednosti granice razvlačenja.In this work it is shown the effect of heat treatment (annealing at 900 °C in duration 15 and 30 minutes) on microstructure, microhardness and mehanical properties of Cu - 9,1Al alloy. This alloy represents prealloy for production of Cu - Al - Mn - Zn alloy with the shape memory effect. At first it was produced ingot with dimensions Ø 110 x 180 mm which is remelted and continously casted in the shape of cylindrical rod with diameter 8 mm. EDS analysis of chemical composition has affirmed that cast of Cu - 9,1Al alloy is successfully done (alloy with homogeneous composition is produced). With optical and scanning electron microscopy was observed existence of dual-phase α + β microstructure which preserves after heat treatment as well although certain sporadic shape changes of α - phase occurs. On DSC analysis was noticed one endothermic change of the heat flow during the heating which probably represents β→α transformation and one exothermic change of the heat flow during the cooling which probably represents β→α transformation. Differences observed in the microhardness and tensile strength values are insginificant while the strain decreases with longer duration of the annealing. Changes in the amount of contraction coincides with changes in the value of the yield strenght