Merging the Computational and Experimental Gravity Poles of the Alloy Development Process: From Alloy Design to In-Situ Alloying of Custom Al Alloys for Laser Powder Bed Fusion

Recent progress in metal additive manufacturing (AM) emphasised the need to develop next-generation alloys leveraging the non-equilibrium dynamics of rapid cooling processes. This raised the awareness among the leading industrial players of the AM scene that boosting the material palette for AM is the way to unlock the full potential of additive manufacturing in vital application sectors, such as aerospace, energy, and defence. In fact, functional parts with enhanced strength, good electrical and thermal resistance, and low density are often targeted for these critical applications, and the current alloys in the market might not meet these requirements. Therefore, driven by these motivations, novel aluminium alloy grades for use in Laser Powder Bed Fusion (PBF-LB) are currently sought.<br/><br/>An industrially relevant commercial Al alloy system used in targeted industrial sectors was selected in the alloy design stage. The chemical composition of such alloy was tweaked by adding a reinforcing transition metal (TM) element that enhanced the master alloy’s strength by multiple strengthening mechanisms. Computational design tools based on the CALPHAD approach enabled the chemical process window's fast selection for the new aluminium grades. The solidification trajectories of various TM-dosed Al grades were assessed for conditions deviating from the equilibrium using the Scheil-Gulliver assumptions to predict the alloy’s precipitation sequence, crack sensitivity, and printability.<br/><br/>The computational predictions were empirically corroborated with targeted experiments involving arc-melted buttons' production in generating the corresponding Al-TM master alloys. The microstructure resulting from the fast-cooling rates of the PBF-LB process was simulated by surface remelting in an industrial printer. Hierarchical microstructure investigations conducted at all length scales from macro- to nano showed a satisfactory level of correlation with computational predictions, and the final transition metal element amount was eventually established based on considerations involving strengthening mechanisms, hot crack sensitivity, PBF-LB processability, and heat-treatment design strategies.<br/><br/>The developed Al-TM alloy was then manufactured by laser powder bed fusion in-situ alloying achieving near fully dense samples. At this stage, nano-particles were introduced in the newly developed metal matrix to further enhance strength and its thermal stability at temperatures higher than 300 degrees celsius. The process-structure-performance relationships of the Al-xTM alloy with and without nanoparticle additions were deeply studied at the possible environmental working conditions (RT and elevated temperatures).<br/><br/>The outcomes of this research prove that new high-strength Al alloy compositions can be established by exploring unconventional design spaces enabled by the fast-cooling rates of additive process<b>es</b>. The combined computational-experimental method utilised in this study provided a fast and robust guidance towards the development of printable high-strength Al alloys for Laser Powder Bedd Fusion.