Exceptional Grain Refinement in Directly Built up Sc-Modified AlMg-Alloys Is Promising a Quantum Leap in Ultimate Light Weight Design

Additive manufacturing technologies like selective laser melting (SLM) are more or less purely welding actions which feature micro structures similar to cast structures coupled with inherently high cooling rates during solidification (10³ – 10⁵ K/sec).  A Sc/Zr modified AlMg alloy concept (“ScalmalloyRP”) ideally suited for SLM due to its readily weldability was developed with the aim to compete with 3-dimensional high speed cutting AA7050 T7451 plate or forged machining solutions. Comprehensive material characterization after build up revealed exceptional fine – ultra fine grained cast bimodal micro structures with impressing material properties which can outperform standard 7xxx & 2xxxLi aerospace plate materials. Derived from metallography, SEM & TEM investigations a model was developed to explain this important technical attribute caused by the layer wise local melting (welding) procedure. Beside solidification grain refinement, causing Hall-Petch strengthening, precipitation hardening based on the coherent L₁₂ – phase Al₃Sc(Zr) contributes to the recorded strength values, astonishingly not compromising toughness & ductility. In addition the AlMgScZr alloy has a 7% lower density and no stress corrosion cracking constraints compared to those incumbent Al-plate alloys.