The effect of heat treatment on the structure and corrosion resistance of Al-Zn-Mg alloys

The parameters of heat treatment of Al-Zn-Mg alloys subjected to precipitation hardening have a substantial impact on mechanical and corrosion resistance. The rate of cooling after supersaturation, along with the ageing temperature and time, affect significantly mechanical properties of these alloys. The type of ageing (artificial or natural) after saturation implies corrosion resistance in seawater. Being a modification of the AlZn5Mg1 alloy, denoted as PA47, the AlZn5Mg2CrZr alloy reveals best mechanical properties among all aluminium alloys in shipbuilding [1]. However, the higher level of precipitation hardening, the higher susceptibility to corrosion, in particular to stress corrosion cracking (SCC). Describing the structure of Al-Zn-Mg alloys by identifying the precipitation free zone (PFZ) and the Guinier-Preston (G-P) zones provides the information on the corrosion resistance of these alloys.