Cracking mechanism and its sensitivity to processing conditions during laser powder bed fusion of a structural aluminum alloy

Abstract

Abstract In this paper, an analysis of the hot cracking susceptibility as a function of processing parameters is presented for the structural aluminum alloy 6061 (Al-0.8Si-1.2Mg %wt) processed by laser powder bed fusion (L-PBF). The hot cracking mechanism is identified as solidification cracking on the basis of experimental observations in as-built microstructures. In agreement with previous works, cracks are found to occur at high angle grain boundaries and are preferentially located at the center of the melt pools. Using the Rappaz-Drezet-Gremaud model combined with Rosenthal simulations, we show that the location of hot cracks corresponds to the regions of highest mechanical solicitation during solidification. Hot cracking sensitivity maps are then developed to predict in a simple manner the variations of hot cracking susceptibility as a function of the first order process parameters, namely the laser power and scanning speed and as well for the preheating conditions. The predicted trends are qualitatively in agreement with the experimental observation. The results allow the impact of processing conditions on reducing hot cracking to be discussed.