Laser printing path and its influence on molten pool configuration, microstructure and mechanical properties of laser powder bed fusion processed rare earth element modified Al-Mg alloy

This work investigated the influence of laser scan strategy, which essentially determines the molten pool path, on microstructure evolution, residual stress and mechanical properties of the LPBF processed Al-4.2Mg-0.4Sc-0.2Zr alloy. Laser scan strategies including parallel, bi-directional, island and remelting modes were applied for comparison. The remelting specimen exhibited a relatively smooth surface with Ra = 10.2 ± 0.9 μm combined with minimum residual stress of ϵ = 0.195, which was attributed to the decreased temperature gradient within the molten pool during the remelting process. The tensile properties for the remelting mode were decreased from 500 MPa to 473 MPa combined with elongation reduced from 15% to 7% compared to those of the other strategies. It was mainly caused by the precipitation coarsening, which further changed the strengthening mechanism from precipitate shearing to Orowan dislocation looping mechanism. This study proves that the surface roughness, residual stress and properties can be well tailored through optimising laser scan strategies.