The hot stretch forming of sheet metal alloys, such as highly deformable aluminum alloy materials, is improved by using a lubricant comprising bismuth between the forming tool and the engaged surface of the sheet metal. A precursor of bismuth, such as bismuth subsalicylate, may be dispersed in a liquid and applied to the sheet metal before the sheet is heated to its forming temperature. Other lubricants such as boron nitride may be combined with the bismuth precursor. The precursor compound is decomposed to bismuth (or bismuth and carbon in the case of bismuth subsalicylate) which lubricates contact between the surface(s) of the sheet and the forming tool during forming and removal of the formed part from the tool.