Cryogenic Forming of Al‐Mg Alloy Sheet for Car Outer Body Applications

Abstract

During deep‐drawing of Al‐Mg sheet at room temperature, stretcher‐strain marks can appear on the material's surface. Such parts are not suitable for car outer body applications because the visually unappealing marks are still visible after painting. In this paper, the occurrence of surface marks on a miniaturized engine hood is significantly reduced by deep‐drawing at approximately −180 °C. Yield strength, ultimate tensile strength, and tensile elongation are significantly higher at cryogenic temperature and the Portevin–Le Chatelier effect disappears. Scanning electron microscopy of fracture surfaces reveals that the ductile fracture mechanism is similar at cryogenic temperature and room temperature. However, the localized ductility is reduced at cryogenic temperatures, resulting in a finer structure of the fracture surface. In summary, cryogenic forming permits the use of Al‐Mg alloys for producing outer body car parts with acceptable surface quality.