The effects of Cu addition of 0.38, 3.82, and 6 wt. % in Al-7Si-4Mg alloy on hardness and age hardening response were discussed. Samples were solution treated at 495 °C for 2 h, quenched, and aged at 130 °C for 0 to 498 h. Characterization included hardness test, microstructural observation by an optical microscope (OM) and Scanning Electron Microscope (SEM) combined with Energy Dispersive X-Rays Spectroscopy (EDX), as well as Simultaneous Thermal Analysis (STA) testing. The results showed an increased in as-cast hardness along with addition of Cu. Peak hardness increased to 64.47, 65.8, and 70.1 HRB by addition of 0.38, 3.82, and 6 wt. % Cu, respectively. The addition of Cu promoted the formation of Al2Cu and Al5Cu2Mg8Si6 which contributed to higher as-cast hardness. Formation of GP-zone, θ", and θ' was observed after ageing at 48, 240, and 290 °C, respectively and no effects of Cu was detected on the formation temperatures of the precipitates.