Enhancing the mechanical performance of aluminum alloys

Laser powder bed fusion (LPBF) is a prominent additive manufacturing (AM) process that fuses thin layers of metal powder to underlying layers using laser melting in a sequential process. However, the high cooling rates and peak surface temperatures of the LPBF process can cause solidification defects in lightweight materials such as aluminum (Al) alloys, which have poor mechanical performance at elevated temperatures. To overcome these limitations, researchers are working to develop unique material compositions that can exploit the benefits of LPBF while improving performance of the final component.

To this end, Lawrence Livermore researchers and collaborators have generated a nanoscale microstructure that results in improved hardness and tensile strength and mitigated solidification cracking in as-cast material and LPBF-fabricated components. During the experiment, the team investigated the microstructural and mechanical properties of LPBF-AM fabricated components and single laser tracks in a recently reported class of Al alloys containing cerium (Ce) and magnesium (Mg)—AlCeMg—with a combination of ultrafast in situ x-ray imaging, ultra-small-angle x-ray scattering, scanning electron microscopy, nanoindentation, and uniaxial tension testing. The in situ x-ray imaging show the nanostructure arises from laser-induced melting of intermetallic particles embedded into the alloy during casting and then rapid resolidification of the molten material. Microscopy and retention of tensile properties show the formed nanostructures are highly resistant to thermal coarsening at high temperatures.

The formation of a Ce-rich, thermally stable nanostructure during LPBF-AM of AlCeMg alloy provides a pathway to enhanced mechanical performance of Al alloy components even after exposure to typically adverse thermal environments. These results pave the way for development of AM-specific Al alloys that possess the ability to form mechanically favorable nanostructures for applications in the transportation and aerospace industries.

This project received funding from the Laboratory Directed Research and Development program (17-ERD-042).

[A.A. Martin, J.A. Hammons, H.B. Henderson, N.P. Calta, M.H. Nielsen, C.C. Cook, J .Ye, A.A. Maich, N.E. Teslich, T.T. Li, M.J. Thompson, M.F. Besser, M.J. Matthews, R.T. Ott, O. Rios, S.K. McCall, T.M. Willey, and J.R.I. Lee, Enhanced mechanical performance via laser induced nanostructure formation in an additively manufactured lightweight aluminum alloy, Applied Materials Today 22, 100972 (2021), doi: 10.1016/j.apmt.2021.100972.]