Abstract
Aluminum alloys processed through selective laser melting possess unique features of microstructure, defect morphology and mechanical properties. Constitution of fine cellular dendrites results from the high-cooling rate of the melt pool during the consolidation process. Investigation of the microstructure by scanning electron microscopy identifies supersaturation of Si particles as a secondary strengthening mechanism. On the contrary, platform heating that induces coarser microstructure leads to migration of Si particles from the Al matrix to the eutectic phase. As a result, tensile strength is reduced by ~3%, while fracture strain is increased by ~17%. Fine-grained structures exhibit a lower amount of plastic damage accumulation as well as delayed crack initiation as determined by the applied measurement techniques. Finite element models of the investigated configurations are obtained using scans of computed tomography under consideration of process-induced defects. Comparison of modeling and experimental results concluded that dominant fatigue damage mechanisms are related to the loading regime from low-cycle (LCF) to very-high-cycle fatigue (VHCF). Thus, process-inherent features of microstructure and porosity have different quantitative effects concerning the applied load. In VHCF, a material configuration with platform heating possesses an improved fatigue strength by ~33% at 1E9 cycles, concerning the material configuration without platform heating.
Highlights
Production of metallic components using layer-wise build-up in powder-bed-fusion processes, like selective laser melting (SLM), made the most significant progress from rapid prototyping into rapid manufacturing applications [1,2]
The current study aimed at investigating efficient testing strategies to qualify additively manufactured aluminum alloys
AlSi10Mg and AlSi12, were investigated with platform heating as the main factor. The latter factor is identified in the previous literature as a control parameter to reduce remnant porosity and coarsen microstructure [10,11]
Summary
Production of metallic components using layer-wise build-up in powder-bed-fusion processes, like selective laser melting (SLM), made the most significant progress from rapid prototyping into rapid manufacturing applications [1,2]. Edwards and Ramulu found fatigue strength of as-built SLM Ti-6Al-4V inferior to the wrought alloy due to porosity and residual stresses [3]. Cain et al reported that mechanical properties have a significant directional anisotropy. The observation was attributed to anisotropic microstructure with a strong gradient in the cooling direction. Effect of residual stress distribution in the asbuilt specimens was most significant in the fatigue crack growth rate and fracture toughness. Relaxation of residual stresses by post-process annealing reduced anisotropy and increased fracture toughness [1]
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