Effects of Cu addition on the precipitation hardening response and intergranular corrosion of Al-5.2Mg-2.0Zn (wt.%) alloy

Effects of 0.45 wt.% Cu addition on the precipitation hardening response and intergranular corrosion (IGC) of Al-5.2Mg-2.0Zn (wt.%) alloy have been investigated in this research. Results suggest that, on one hand, Cu addition improves the age hardening response of Al-5.2Mg-2.0Zn alloy significantly by stimulating the precipitation of GP zones during pre-aging treatment, which results in finer dispersion of the T-Mg32(Al, Zn)49 (Im3, a = 1.422 nm) phase in peak aged condition. The higher peak hardness results from the higher density and finer T phase inside grain, increased strengthening ability of the T phase and the narrower width of precipitation free zones (PFZ). Though Cu addition has no effect on the precipitation kinetics of the T phase, it improves the thermal stability of the T phase. On the other hand, the improved IGC resistance of the Al-5.2Mg-2.0Zn-0.45Cu alloy is due to the narrower width of PFZ and increased corrosion potential combined with decreased corrosion current density. Higher volume fraction of precipitates inside grain may also contribute to the improved IGC resistance by reducing the corrosion potential difference between the grain and the PFZ.