[Aluminium memiliki sifat yang ringan dan tahan korosi, sehingga banyakdigunakan di bidang manufaktur. Penggunaan material aluminium sangat efektifuntuk meningkatkan efisiensi turbin pembangkit tenaga listrik Organic RankineCycle (ORC). Aluminium seri 7xx (Al-Zn) merupakan pilihan yangdiperhitungkan pada turbin ORC karena memiliki kekuatan yang tinggi dibandingseri lainnya. Untuk lebih meningkatkan kekuatan Al-Zn, ditambahkan unsur Mgdan Cu serta pemberian laku pengerasan penuaan.Penelitian kali ini mempelajari pengaruh penambahan Cu sebesar 0, 1, 3 dan 5wt.% pada paduan Al-9Zn-4Mg (wt.%). Paduan dibuat dengan proses investmentcasting pada cetakan berbentuk impeller turbin. Pada paduan dilakukan proseslaku pelarutan pada temperatur 460 oC selama 2 jam dan dilanjutkan prosespenuaan pada temperatur 130 oC. Karakterisasi meliputi pengujian kekerasanuntuk mengamati respon pengerasan penuaan, pengamatan struktur mikro danpengujian Differential Scanning Calorimetry (DSC). Struktur mikro diamatimenggunakan mikroskop optik dan Scanning Electron Microscope (SEM) yangdilengkapi dengan Energy Dispersive Spectroscopy (EDS).Hasil penelitian menunjukkan bahwa penambahan Cu ke dalam paduan Al-9Zn-4Mg menurunkan kekerasan awal (2 jam) akibat segregasi kompeks Cu-V kebatas butir yang akan melunakkan dan memperlebar batas butir, Namunkandungan penambahan Cu meningkatkan kekerasan puncak, walau tidak terlalusignifikan akibat tingginya kandungan Zn dan Mg. Selama pengerasan penuaanterjadi reaksi eksotermik yaitu pembentukan GP zone, presipitat η’ (MgZn2) danpresipitat η (MgZn2) serta reaksi endotermik dari dissolution GP zone danpresipitat η. Sementara, fasa kedua yang ditemukan adalah MgZn2 dan Al7Cu2Fedi batas butir., Aluminium is a light-weight material and possesse high corrosion resistance, sothat it is widely used in manufacturing industries. Aluminium alloy is a candidateto be used as turbine impeller in an Organic Rankine Cycle (ORC) power plantsystem. Al 7xx series (Al-Zn) has the highest strength compared to otheraluminium series, therefore it is suitable for ORC turbine. To futher increase thestrength of Al-Zn alloys, Mg and Cu are added as well as age hardening treatment.This research studied Al-9Zn-4Mg alloys with Cu content of 0, 1, 3 and 5 wt.%.The alloys were produced through investment casting taking the shape of turbineimpeller. The samples were solution treated at 460 oC for 2 hours and then aged at130 oC. The characterization included hardness testing to observed response ofage hardening, microstructural observation and Differential Scanning Calorimetry(DSC) testing. Microstructural observation was conducted by optical microscopeand Scanning Electron Microscope (SEM) which was combined with EnergyDispersive Spectroscopy (EDS).The results showed that addition of Cu initially decreased the hardness duringearly ageing ( 2 hours) due to segregation of Cu-V complexes toward the grainboundaries which then decrease the hardness and enlarge the grain boundaries.However, the peak hardness is increased by addition of Cu although not assignificant due to high concentration of Zn and Mg. exothermic reaction offormation of GP zone, η’ (MgZn2) and η (MgZn2) was found during precipitationprocess while endothermic reaction were observed due to dissolution of GP zoneand η (MgZn2). Presence of MgZn2 and Al7Cu2Fe were also observed in grainboundaries.]