Heat treatment of aluminium alloy high pressure die castings

A method for the heat treatment of a high pressure die cast casting which exhibits gaseous or other porosity and is of an age-hardenable aluminium alloy having 4.5 to 20 wt % Si, 0.05 to 5.5 wt % Cu, 0.1 to 2.5 wt % Fe, 0.01 to 1.5 wt % Mg, at least one of Ni up to 1.5 wt %, Mn up to 1 wt % and Zn up to 3.5 wt %, and a balance of aluminium and incidental impurities, wherein the method comprises the steps of:

• (a) heating the casting, which is made by conventional high pressure die casting without application of high vacuum or use of a reactive gas, to and within a temperature range that allows solute elements to be taken into solid solution (solution treatment), wherein the heating is:
• (i) to and within a range of from a temperature of 20° C. below the solidus melting temperature for the alloy of the casting to a temperature of 150° C. below the solidus melting temperature for the alloy of the casting, said temperature of 20° C. below the solidus melting temperature being a temperature not exceeding 525° C., and
• (ii) for a period of time of less than 30 minutes;
• (b) cooling the casting from the temperature range for step (a) by quenching the casting into a fluid quenchant at a temperature between 0° C. and 100° C.;
• and
• (c) obtaining a hardened or strengthened casting that is at least substantially without blistering by ageing the quenched casting from step (b) in a natural or artificial ageing temperature range of from 0° C. to 250° C.