Investigation of Creep Behaviour of Al-9Zn-4Mg and Al-9Zn- 4Mg-5Cu Alloys

Two aluminium alloys, Al-9Zn-4Mg and Al-9Zn-4Mg-5Cu was prepared for candidate material impeller turbine radial inflow system Organic Rankine Cycle (ORC) that works at 130 °C. The temperature is high for aluminium alloys so the creep behaviour of the alloys have to investigated. This study identified creep resistance of the alloys and also investigated the creep mechanism of the alloys. Creep test conduct at 50 MPa and variation temperature 150, 200 and 250 °C. The fracture surface and microstructure of subsurface was examinated by SEM. The creep test result showed both of alloys did not failure at 150 °C while Al-9Zn-4Mg-5Cu has a good creep strength compare with Al-9Zn-4Mg at temperature 200 and 250 °C. The fracture surface and microstructure of subsurface indicate the coble creep mechanism or difusional creep. The good creep strength of Al-9Zn-4Mg-5Cu due to CuAl₂ phase serves as a pin which inhibit the rate of diffusion at the grain boundaries. (paper)