Lubricant for elevated temperature forming

A method of forming aluminum alloy sheet material at an elevated temperature, the method comprising:

• providing an internally heated forming tool comprising a forming surface at a forming temperature for an aluminum alloy sheet metal workpiece;
• providing an aluminum alloy sheet metal workpiece having a first surface for engagement with the forming surface of the forming tool, and an opposing surface;
• applying a lubricant coating comprising bismuth to at least one of the forming surface of the forming tool or the first surface of the sheet metal workpiece;
• heating the aluminum alloy sheet metal workpiece to a forming temperature in excess of 200° C.;
• and
• producing a shape in the aluminum alloy sheet metal workpiece by applying a pressurized working gas to the opposing surface of the sheet metal workpiece so that the first surface of the sheet metal workpiece is deformed into conformance with said forming surface, the bismuth-containing lubricant acting between the first surface of the metal sheet and the forming surface of the tool.