Materialuntersuchungen einer für LPBF optimierten Al-Fe-Zr Legierung im Hinblick auf die Etablierung von Prozessparametern für spezifische Anwendungsfälle

Abstract

The present work focuses on developing the capabilities for processing the Constellium Aheadd® CP1 alloy on a Concept Laser® M2 additive manufacturing setup equipped with a 400 W NdYAG laser and on developing a fundamental understanding of the obtained material. A parameter study to establish processing windows for varying layer thicknesses (30 µm, 60 µm and 120 µm) was performed first. The resulting microstructures were analyzed. In addition, the effects of a remelting strategy, in which the already solidified material was exposed to the laser radiation again, were investigated. The studies showed that layer thicknesses of 60 µm and 30 µm are especially suitable for manufacturing samples with a porosity of less than 0.15 %. The widest and, thus, most robust process window was given with a layer thickness of 30 µm at a laser power of 390 W. Re-exposure of the already solidified layers can help to reduce bonding defect porosity. A build platform position dependence was observed, which indicates a local attenuation of the input energy. Porosity due to excessive energy input can be reduced by exposing the layers twice at double the scan speed. The formation of the microstructure seems to depend in particular on the size of the hatch spacing and the resulting overlap of the melt tracks. A large hatch spacing, in combination with a high energy input, contributes to the formation of the bimodal microstructure which is well known for LPBF-manufactured Al alloys. A small hatch spacing can be associated with the formation of a more homogeneous fine microstructure. The size of the grains depends on the energy density. In order to analyze the suitability of the manufacturing process for specific applications, like filigree heat exchangers, specimens mimicking special structures were fabricated and particularly the role of the layer thickness for the quality was studied. Thin structures can be manufactured using a layer thickness of 60 µm and 30 µm, but using 30 µm the quality of the fabricated parts is highest. The thinnest structure that could be manufactured has a thickness of 0.3 mm which corresponds to 0.6 mm thickness of the CAD-model.