Improving the Defect Tolerance and Fatigue Strength of AM AlSi10Mg

Additively manufactured structures reveal a poor surface quality and a high number of process-induced defects in the surface-near area, leading to a significant reduction of the fatigue strength. As laser-based powder bed fusion (PBF-LB) processes are used to produce topologically optimized lightweight structures with complex geometries, which cannot be fully machined, the influence of the process-induced surface on the fatigue behavior needs to be analyzed. For this, also the interrelation of the surface-induced notch effects with the surrounding material volume must be considered. As thermal treatments can also be applied to filigree components with complex geometries, in the presented work the influence of different heat treatments, i.e., stress relief annealing (SR) and artificial aging (T6), on the material properties, especially the defect tolerance, of AlSi10Mg manufactured via PBF-LB is analyzed. Both heat treatments lead to a dissolution of the cellular Si-rich network, resulting in decreased hardness and tensile strength, but higher fatigue strength. The increased fatigue strength results from a reduction of the process-induced residual stresses, but mainly a strongly improved defect tolerance. Consequently, to evaluate the fatigue strength of additively manufactured materials, besides the materials strength and the process-induced defects, also the defect tolerance must be considered.