Forming-Limit Diagrams for Hot-Forming of AA5083 Aluminum Sheet: Continuously Cast Material

Fine-grained AA5083 aluminum sheet is used for hot-forming automotive body panels with gas pressure in the superplastic forming (SPF) and quick plastic forming (QPF) processes. Deformation under QPF conditions is controlled by two fundamental creep mechanisms, grain-boundary-sliding (GBS) and solute-drag (SD) creep. The failure mechanisms of AA5083 materials under QPF conditions depend strongly on these deformation mechanisms and on the applied stress state. Failure can be controlled by flow localization, cavitation development or a combination of both. There is interest in using continuously cast (CC) AA5083 materials instead of direct-chill cast (DC) materials in QPF operations as a means of reducing material cost. However, CC and DC AA5083 materials can produce significantly different ductilities under hot forming. Rupture-based forming-limit diagrams (FLDs) have been constructed for a CC AA5083 sheet material under hot-forming conditions. Forming limits are shown to be related to the controlling deformation mechanisms. Differences between FLDs from DC and CC AA5083 materials are investigated. The differences in FLDs between these materials are related to differences in cavitation development.