The effect of heat treatment on mehanical properties of CuAlMn shape memory alloy

U ovom radu je prikazan utjecaj toplinske obrade na mikrostrukturu i mehanička svojstva CuAlMn legure s prisjetljivosti oblika. Legura kemijskog sastava Cu – 8,30 % Al – 9,4 % Mn (mas.%) je pripremljena iz čistih metala (>99,5 %), a zatim lijevana kontinuiranim vertikalnim postupkom u zaštitnoj atmosferi argona. Najprije je proizveden ingot (Ø 110 x 180 mm) koji je korišten kao ulazni materijal za lijevanje šipke promjera Ø 8 mm. Provedena su ispitivanja vlačne čvrstoće, granice razvlačenja, istezanja, kontrakcije i tvrdoće nakon lijevanja, kaljenja (900 °C/30'/H2O) i popuštanja (100 – 300 °C/60'/H2O). Mikrostrukturna karakterizacija uzoraka legure provedena je optičkom mikroskopijom (OM) i pretražnom elektronskom mikroskopijom (SEM) s EDS analizom. S pretražnim elektronskim mikroskopom je također provedena analiza prijelomnih površina. Nakon lijevanja CuAlMn legure vlačna čvrstoća je iznosila 627 MPa, istezanje 8,5% i kontrakcij a 17,88 %. U lijevanoj leguri utvrđena je djelomična prisutnost martenzitne faze dok je nakon kaljenja mikrostruktura u potpunosti bila martenzitna. Značajan porast vlačne čvrstoće i značajan pad istezanja uočeni su nakon popuštanja 200 °C/60'/H2O i 300 °C/60'/H2O.This paper shows the effect of heat treatment on microstructure and mehanical properties of CuAlMn shape memory alloy. Alloy with the chemical composition of Cu – 8.30 Al – 9.4 % Mn (wt.%) was prepared from pure metals (>99.5 %) and then the alloy was casted by continuously vertical casting tehnique, under protective argon atmosphere. The prepared ingot (Ø 110 x 180 mm) was used as an input material for casting into 8 mm diameter bars. The tensile strength, yield strength, elongation, reduction in area, and hardness were examined after casting, quenching (900 °C/30'/H2O), and ageing (100 – 300 °C/60'/H2O). The samples were microstructurally analysed using optical microscopy (OM) and scanning electron microscopy (SEM) along with EDX analysis. Using scanning electron microscopy fracture surfaces were also tested. Test resulted in tensile strength of 627 MPa, elongation of 8.5% and reduction in area of 17.88% after casting of CuAlMn shape memory alloy. The alloys revealed some martensitic phase after casting, but after quenching microstructure was completely martensite. The tensile strength drastically increased and elongation drastically decreased after ageing at 200 °C/60'/H2O and 300 °C/60'/H2O