Method of forming parts from sheet metal alloy

A method of forming a part of complex shape from sheet metal alloy, the method comprising the sequential steps of:

• (a) heating the sheet to a temperature at which solution heat treatment of the alloy occurs so as to achieve solution heat treatment;
• (b) controlling a cooling rate of the sheet to at or above a critical cooling rate of the alloy until a target temperature is reached based on a measured temperature at one or more positions, where the cooling rate is controlled by:
• measuring the temperature of the sheet at the one or more positions on the sheet,
• comparing the measured temperature with a reference temperature, where the reference temperature defines a rate of cooling at which microstructural precipitation in the alloy is avoided, and
• cooling the sheet by applying a cooling medium to at least a portion of the sheet,
• wherein the target temperature is 250° C. to less than 450° C.,
• wherein the cooling rate of the sheet is controlled by adjusting a flow rate of the cooling medium applied to at least a portion of the sheet by increasing the flow rate of the cooling medium when the measured temperature is decreasing at a rate lower than a rate of the reference temperature, and decreasing the flow rate of the cooling medium when the measured temperature is decreasing at a rate higher than the rate of the reference temperature;
• (c) placing the sheet between dies to form it into or towards the complex shape;
• and then
• (d) quenching the sheet between the dies, whilst the dies are in contact with the sheet.