Secondary Aluminum Alloys Processed by Semisolid Process for Automotive Application

Abstract

OEMs manufacturers of aluminum based safety components for automotive sector are used to require low percentage of Fe as contaminant, since it can be responsible of very high brittle microstructure due to formation of acicular Fe-compounds. Lowest Fe percentage is achieved by alloying primary aluminum, instead of secondary aluminum obtained on recycling marketplace. On the other hand, any aluminum alloys fabricated starting from primary aluminum achieves very high environmental impact, due to very high CO2 equivalent emitted during the early extractive stage. In order to reduce total global warming potential of finished components, recycling alloys would be preferred, but metallurgy solutions are necessary to control Fe-contaminants. According to recent advancements, Fe-compounds in recycled aluminum could be controlled throughout semisolid processes, where the stirring phase of a semisolid slurry would produce fragmentation Fe-compounds. In this work, investigation about key process parameters has been performed to correlate microstructural features to mechanical properties in presence of Fe-compound. Among various process parameters, stirring time and solid fraction are most important key parameters to control to obtain fine globular microstructure. Tensile tests have been performed showing promising results (yield strength about 300 MPa and ultimate tensile stress about 330 MPa). Stirring stage in semisolid process allows reduction of average size of Fe-compounds, thus producing an increase in percentage elongation and toughness, namely the main requirements in automotive sector for widespread use of low-cost and low-environmental impact aluminum alloys.