Combination of Precipitation and grain Refinement for the Achievement of high Strength Aluminium alloys – PRASA

Aluminium alloys play an important role in the transportation industry. In the aircraft or the car industry, the demand for high strength alloy to design low weight structures is nowadays strongly driven by energy savings and low CO2 emissions. Thus developing, optimizing and producing new alloys with enhanced properties is one of the key factors for the competitiveness of this industry, including metal processing as well as forming. The present proposal deals both with fundamental research to develop the initial concepts and develop an “alloy by design” approach and with more applied research seeking to demonstrate the possibility for industrialization. We will develop and optimize an up-scaled severe plastic deformation (SPD) process named sheet-ECAP able to process at a large scale ultrafine grained aluminium alloys with an alloy composition specifically designed for this process, providing a better thermal stability of the fine grain structure together with a combination of nano-scaled precipitates. The target is to obtain high strength aluminium alloys (up to 800 MPa) with a uniform elongation ranging to 10%. From a fundamental point of view, special emphasis will be given to precipitate hardening mechanisms in nano-scaled grains. To achieve these goals, it is proposed to combine an experimental approach using up-to-date characterization techniques (TEM, EBSD, APT, SAXS) with modelling (grain refinement, structure/properties relationship). One of the innovative aspects of this project is that we propose to adapt the chemical composition of an aluminium alloy to optimize the stability of the UFG structure and the precipitation of nano-scaled precipitates within grains. The project is based on the idea to design alloys with a relatively high concentration of Fe leading to the formation of a significant volume fraction of intermetallic particles, and take advantage of the SPD process to break them into small particles, efficient to pin the ultra fine grain structure during the precipitation treatments. We will also explore the possibility to create nano-scaled precipitates through the formation of super saturated solid solutions induced by SPD and thus creating a structure that cannot be achieved by classical metallurgical processes. Thus, our methodology will provide a unique opportunity to transform low purity recycled Aluminium enriched in iron into high strength aluminium. The project is organized in four work packages, from a very fundamental approach on a model Al-Fe alloy with a progressive move to commercial alloys (AA2050, AA7449) with optimized Fe contents and last the process optimization (sheet-ECAP). This project is also based on the complementary approach and expertise of scientists from three different French laboratory (GPM, SIMAP and LEM3). This is multidisciplinary consortium, ranging from mechanics to physics and chemistry of materials. It gathers experts in light alloy characterization using various experimental techniques, mechanics of materials, ultrafine grain structures, precipitation in Al alloys and processing. One of the fundamental aspects of the present proposal will be also treated in collaboration with the research team of Prof. Zenji Horita (Kyushu University, Japan). Last, this project is also supported by Constellium (aluminium industry) that will supply the industrial material for the studies.