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  • Microstructure, mechanical ...
    Mehta, Bharat; Mishurova, Tatiana; Evsevleev, Sergei; Markötter, Henning; Bruno, Giovanni; Hryha, Eduard; Nyborg, Lars; Virtanen, Eero

    Materials & design, 02/2023, Letnik: 226
    Journal Article

    Display omitted •7017 Al alloy admixed with 3 wt% Zr, 0.5 wt% TiC created fully dense samples (<0.2 % porosity) processed via PBF-LB process.•Microstructure shows strengthening as a combination of precipitation hardening and grain size strengthening.•In-situ combined with ex-situ tensile testing confirm Zr inclusions improve ductility by deflecting crack growth. This study addressed a 7017 Al-alloy tailored for powder bed fusion – laser beam (PBF-LB) process. The alloy was prepared by mixing 3 wt% Zr and 0.5 wt% TiC powder to standard pre-alloyed 7017 grade aluminium powder. This made printing of the alloys possible avoiding solidification cracking in the bulk and achieving high relative density (99.8 %). Such advanced alloys have significantly higher Young’s modulus (>80 GPa) than conventional Al-alloys (70–75 GPa), thus making them attractive for applications requiring high stiffness. The resulting microstructure in as-printed condition was rich in particles originating from admixed powders and primary precipitates/inclusions originating from the PBF-LB process. After performing a T6-like heat treatment designed for the PBF-LB process, the microstructure changed: Zr-nanoparticles and Fe- or Mg/Zn- containing precipitates formed thus providing 75 % increase in yield strength (from 254 MPa to 444 MPa) at the cost of decreasing ductility (∼20 % to ∼9 %). In-situ tensile testing combined with SXCT, and ex-situ tensile testing combined with fracture analysis confirmed that the fracture initiation in both conditions is highly dependent on defects originated during printing. However, cracks are deflected from decohesion around Zr-containing inclusions/precipitates embedded in the Al-matrix. This deflection is seen to improve the ductility of the material.