Experimental and numerical investigations of the hot cracking susceptibility during the powder bed fusion of AA 7075 using a laser beam

The variety of processable materials for the powder bed fusion of metals using a laser beam (PBF-LB/M) is still limited. In particular, high-strength aluminum alloys are difficult to process with PBF-LB/M without the occurrence of hot cracks. In situ alloying is a promising method to modify the physical properties of an alloy to reduce its hot cracking susceptibility. In this work, the aluminum alloy 7075 and blends with 2 wt.%, 4 wt.%, and 6 wt.% of Si were processed via PBF-LB/M. The Rappaz-Drezet-Gremaud (RDG) model and the Kou model were investigated regarding their capability of predicting the hot cracking behavior for the aluminum alloy 7075 and the three powder blends. The smoothed-particle hydrodynamics (SPH) method was used to gain the thermal input data for the RDG model. A clear tendency of a reduced hot cracking susceptibility with an increasing amount of Si was observed in the experiments and in the simulations. A detailed analysis of the type of the hot cracking mechanism in the aluminum alloy 7075 provided several indications of the presence of liquation cracking. The Kou model and the RDG model may be applicable for both solidification and liquation cracking. The presented methodology can be used to investigate any material combination and its susceptibility to hot cracking.