Pengaruh Penambahan 1, 3, 5 wt.% Cu terhadap karakteristik Sudu Turbin Radial Inflow paduan Al-9Zn-4Mg hasil investment casting = Effects of 1, 3, 5 wt.% Cu addition on characteristics of Al-9Zn-4Mg alloy for radial Inflow Turbine Blade produced by investment casting results