Additive Manufacturing And Mechanical Properties Of The Dense And Crack Free Zr-Modified Aluminum Alloy 6061 Fabricated By The Laser-Powder Bed Fusion

For additive manufacturing such as laser powder bed fusion (LPBF), commercial aluminum alloy (AA) 6061 is typically considered unsuitable due to formation of solidification cracking and/or excessive porosity. In this study, to improve buildability/printability of AA6061, 1 wt% of Zr was alloyed to produce Zr-modified AA6061 by LPBF. Powders of unmodified and Zr-modified AA6061 were produced by gas atomization, and utilized as a feed-stock for the LPBF to fabricate specimens for microstructural examination and mechanical testing. The asbuilt unmodified AA6061 exhibited poor printability due to formation of cracks and porosity in the microstructure regardless of LPBF parameters. However, the Zr-modified AA6061 exhibited near full density, with substantial reduction in porosities without any solidification crack for a certain LPBF processing window. The improved printability of Zr-modified AA6061 was attributed to a significant grain refinement, which would reduce the solidification cracking susceptibility by hampering the epitaxial growth of long columnar cracks, as observed in unmodified AA6061. Yield strength, tensile strength and strain-at-failure for the as-built Zr-modified AA6061 were determined to be 210 MPa, 268 MPa, and 26.5%, respectively. These are superior to the tensile properties of AA6061 in O-annealed condition or in as-cast condition. After T6 heat treatment, yield strength, tensile strength and strain-at-failure of Zr-modified AA6061 were determined to be 300 MPa, 327 MPa, and 14%, which were again superior to the tensile properties of wrought AA6061 in T6 heat treated condition. Effects of Zr addition on the buildability/printability improvement and mechanical properties of AA6061 were corroborated by a variety of electron microscopic characterization.