Mg and Cu can significantly improve the strength of Al-Si alloys, but at the same time, they also affect their corrosion resistance. To explore the influence of Mg and Cu on Al-Si alloys, which are based on an Al-7 wt.% Si-0.3 wt.% Mg alloy, electrochemical testing methods were used to analyse the effects of the addition of Mg and Cu on the corrosion resistance of Al-Si-Mg-Cu alloys after T6 heat treatment. The results show that with increasing contents of Mg and Cu and increasing corrosion time, the impedance value of the Al-7 wt.%Si-Mg-Cu alloy decreases, the radius of the Nyquist capacitance loop decreases, the corrosion current density increases, and the corrosion resistance of the alloy tends to decrease. When the content of Mg increases from 0.3 wt.% to 0.5 wt.%, the corrosion current density increases by 3.5%, and when the content of Cu increases from 0 wt.% to 0.65 wt.%, the corrosion current density increases by 10.1%. This indicates that with a slight increase in the contents of Mg and Cu, the corrosion resistance of the alloy slightly decreases. Although the nanophases precipitated by Mg and Cu during the aging process accelerate corrosion, the corrosion damage caused by the addition of a small amount of Mg and Cu to the alloy is relatively light.