BigPatents India

This invention relates to a process for the preparation of Aluminium-Zinc-Magnesium-Mangenese-Zirconium-Silver alloy having improved stress corrosion cracking resistance comprising the steps of : (a) preparing a charge mixture of primary aluminium and A1-9 wt% Mn master alloy; and Al-9.8 wt% Ag master alloy; (b) melting said charge mixture of primary aluminium, Al-9wt% Mn master alloy and Al-9.8wt% Ag master alloy adding to this molten charge elemental pure Zn followed by raising the temperature of the molten charge as herein described; (c) adding of AI-54 wt% Mg master alloy, Mg-28 wt% Zr master alloy in the above sequential order to the above molten charge followed by super heating for a period of about 10 minutes; (d) adding nucleant pellets at reduced temperature for grain refinement; (e) degassing the molten melt to remove dissolved gases and pouring the molten melt under inert gas atmosphere, preferably argon atmosphere, into a pre-heated mould; (f) homogenizing, scalping and rolling the sound billets into plates; (g) solution treating, quenching, and stretching the alloy sheets followed by two-step artificial aging wherein Aluminium-Zinc-Magnesium-Mangenese-Zirconium-Silver (AI-Zn-Mg-Mn-Zr-Ag) alloy comprising of AI-(4.8-5.3) Zn-(1.8-2.3) Mg-(0.2-0.4) Mn-(0.11-0.19) Zr-(0.3-0.8) Ag in wt%.