The student Unai Ibarretxe Lopez obtained an OUTSTANDING CUM LAUDE qualification with 'INTERNATIONAL DOCTORATE' mention and 'INDUSTRIAL DOCTORATE' mention
The student Unai Ibarretxe Lopez obtained an OUTSTANDING CUM LAUDE qualification with 'INTERNATIONAL DOCTORATE' mention and 'INDUSTRIAL DOCTORATE' mention
The student Unai Ibarretxe Lopez obtained an OUTSTANDING CUM LAUDE qualification with 'INTERNATIONAL DOCTORATE' mention and 'INDUSTRIAL DOCTORATE' mention
Thesis title: Hot Stamping of High Strength Alumimum Alloys: New Insights into Prediction of Material Properties and Industrialization of Lightweight Automotive Components
Court:
- Chairmanship: A. Erman Tekkaya (Dortmund University of Technology)
- Vocal: Nikolay Sotirov (Benteler International AG)
- Vocal: Ana Conde Del Campo (CENIM)
- Vocal: Iñaki Hurtado Hurtado (Mondragon Unibertsitatea)
- Secretary: Eneko Saenz de Argandoña (Mondragon Unibertsitatea)
Abstract:
The weight reduction of vehicle parts has been a key priority for meeting the demand of reducing both environmental pollution and fuel consumption, as well as improving safety requirements during crashes. When it comes to find a technological improvement in this matter, material substitution offers the most convenient solution among the existing approaches. While structural components made from high strength steels are the material of choice in the automotive sector, high strength aluminum alloys are being implemented due to their high specific strength. However, the extent of the lightweighting potential and crash performance of aluminum in comparison with other materials is not fully known yet. Moreover, forming aluminum has always been a headache for auto makers due to its low formability at room temperature. One of the promising alternatives is to increase the forming temperature via hot stamping, a well known technological solution for manufacturing steel components, such as beams, bumpers or pillars. Nevertheless, the thermal cycle undergone by steel totally differs from the aluminum due to different heat treatment temperatures, times and hardening mechanisms. A research of these characteristics is a key priority for developing the appropriate forming strategy and a fully operative hot stamping line for aluminum. Unfortunately, the hot stamping of aluminum has not been fully consolidated, nor intensively implemented for high production series of car components, as there is still a big research gap on industrialization procedures and lack of knowledge for the prediction of mechanical properties.
To address this gap, a simplified methodology for assessing the lightweighting capacity and life cycle assessment is proposed in order to select the best material candidates, among which AA6082-T6 and AA7075-T6 can been found. These alloys have been experimentally characterized regarding thermophysical and rheological behavior, where a novel hot tensile test procedure is proposed for improving, overcoming and correcting the main issues related with short flow curves, temperature heterogeneity along the specimen, unsteady strain rate deviations and microstructure changes during hot tensile testing. Furthermore, the influence of heat treatment and process variables on the mechanical properties has been studied in order to determine the optimal working window. A constitutive thermal model has been improved and calibrated to numerically estimate mechanical properties under different hot stamping and heat treatment conditions. Finally, semi-industrial hot stamping trials have been performed with a real automotive component with the aim of validating the lightweighting assessment, material characterization, optimal working window and properties prediction model by analyzing several characteristics, such as crash performance, mechanical properties, corrosion resistance and forming precision regarding geometry.
Hot stamped aluminum components have shown excellent characteristics for been industrialized and implemented as safety car components, and good correlation between experimental and predicted mechanical properties has been found, which has allowed Fagor Arrasate S. Coop. to write technological guidelines for developing fully operative hot stamping lines for high strength aluminum alloys.