A study of the mechanical properties of Al6061-Zr$_{1,2}$ alloy processed by laser beam melting

International audienceThe present paper proposes an experimental study to determine the mechanical properties of an additively manufactured modified A6061 alloy, where the addition of 2 volumic % of Yttrium Stabilized Zirconium (YSZ) to Al6061 base powder allows to fully remove cracks during Laser Beam Melting processing. To this end, Vickers tests, tensile tests, Charpy tests and microstructural analyses are used. With respect to the building direction, a quasi-isotropic response is highlighted, with properties (engineering yield and ultimate strengths) higher than the wrought 6061 alloy. This improvement can be attributed to the extra-fine microstructure, a large dislocation density, and a specific precipitation/solution trapping behaviour associated with the Zr addition. Besides, the alloy showed excellent tensile response reproducibility. Thereafter, effect of post-heat treatments are investigated. Classic T6 from wrought alloys practice allowed to precipitate well known and reported nano β-MgxSiy phases, improving the yield and ultimate strengths, but at the expense of significant grain coarsening. The mechanical properties are further increased through an adapted heat-treatment, specifically designed for this Al6061 modified alloy. Al3Zr hardening nanoprecitates are responsible of the improved yield response observed after an annealing for 2 hours at 400°C. The competition between these different hardening precipitation phases (nano β/ nano Al3Zr) is finally discussed