Effect of different Variables on the Precipitate free Zones Adjacent to Grain Boundry Region in Conventionally Quenched and Aged AI-Zn-Mg Alloys

Agenardenaole aluminium alloys are noted for their high strength to weight ratio. Interest on the agehar-denable alloys based on the aluminium -zinc- magnesium system stems from the fact that they have the highest static strength of known aluminium alloys; a noticeable feature of this alloy is the "precipitate-free" zone formed adjacent to grain boundaries. Electron micro-
scopic studies have shown that the stress-corrosion susceptibility and the lack of ductility of aged Al-Zn-Mg_alloys are normally associated with these soft precipitate - free zones adjacent to, grain boundaries. When the alloys are deformed, the precipitate-free zones serve as favourable sites for dislocation movement and this may lead to preferential 'flow in these regions and ultimately to intercrystalline failure.