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Powder bed fusion - laser beam (PBF-LB) of Mg alloy WE43 (Mg-4wt%Y-3wt%RE-Zr) has great potential for the development of future biodegradable metal implants, as well as aerospace lightweight materials. However, the work published thus far has mainly focused on obtaining a fully dense material, and the understanding of the relationship among the PBF-LB process parameters, structure and the resulting material properties remains limited. Thus, the aim of the thesis was to relate the main PBF-LB processing parameters to the formation of key microstructural features in WE43, and their effect on corrosion and tensile test properties. 

The work was carried out on PBF-LB processing units EOS M100 and EOS M290, and the investigated process parameters included laser power, laser scanning speed, hatch distance and sample wall thickness. 

Depending on the resulting thermal conditions, two main microstructural regions were observed. For process parameters resulting in warmer processes, such as higher laser powers and shorter scan lengths, mainly equiaxed dendritic grains were observed. The grains measured up to 10 µm in maximum diameter and exhibited a weak texture, with the inter-dendritic regions rich in Mg-RE intermetallic compunds. For process parameters resulting in conductive mode melting, mainly a lamellar structure was observed. The lamellar structure consisted in large grains with basal texture, and an intragranular structure where lines of Mg-RE intermetallic compunds precipitated parallel to the melt pool boundary. The larger grains had a maximum diameter of around 60 µm to 100 µm in the build direction, and up to 250 µm in the transverse direction, with a preferential growth along the melt pool.

A larger number of dendritic grains was detrimental to the corrosion properties but resulted in higher tensile strength. The result was ascribed to the higher amount of Mg-RE intermetallics and the smaller grains, strengthening the material, but also causing microgalvanic corrosion. Hot isostatic pressing also resulted in growth of the secondary phases and was thus also detrimental to corrosion properties. While a change in hatch distance (40-60 mm) did not cause any dendritic structure to form, a higher hatch distance resulted in improved corrosion properties, but had minor effect on tensile properties, showing the possibilities of applying hatch distance variations to balance corrosion and tensile properties.

In conclusion, the findings presented here show the possibilities of controlling the microstructure and thus the material properties by changing some of the key PBF-LB process parameters, and the major importance of understanding the relationship among process, structure and material properties of PBF-LB processed WE43.

Powder bed fusion – laser beam (PBF-LB) of magnesium (Mg) alloys, particularly WE43 (Mg-4wt%Y-3wt%RE-Zr), offers promising potential for biodegradable medical implants. This thesis investigates the influence of key process parameters in PBF-LB on the microstructure, residual stress, texture, and mechanical properties of alloy WE43 (Mg-4wt%Y-3wt%RE-Zr). This knowledge is intended to support the continued development and implementation of PBF-LB processed WE43 for applications in biodegradable medical implants. The effects of laser power, hatch distance, build size and orientation, as well as laser scan rotation, were systematically investigated. 

Increased energy input through higher laser power promoted equiaxed dendritic grain formation, which enhanced tensile strength. Hatch distance could be optimized to maintain tensile properties even at lower laser powers, and influenced grain size, texture and distribution of secondary phases. Build direction had a large impact on the magnitude of the residual stresses, with larger builds in the vertical direction giving larger stress gradients throughout the sample. Tensile residual stresses were observed at the sample edges, correlating with reduced hardness in those regions compared to the bulk.

Horizontally built specimens showed approximately 40% higher tensile strength (215 MPa vs 150 MPa) and about 20% higher elastic modulus (44 GPa vs 37 GPa) than vertically built ones, primarily due to the development of a strong basal texture along the build direction. This anisotropy implies that part orientation during PBF-LB has a significant impact on performance in service. It was demonstrated that laser scan rotation significantly influences the crystallographic texture, which has the potential to affect the mechanical response of the printed parts. Rotations of 67° and 90° maintain high densification and mechanical integrity while modifying texture. Rotations of 60° and 120° further demonstrate texture control, and a segmented chessboard strategy enhances compressive strength despite weaker texture, due to favourable pore distribution and dendritic grain formation. Conversely, limiting scan rotation to 0° or 180° results in poor densification (<99% relative density), compromising structural integrity. Together, the work included in the thesis provides a comprehensive foundation for PBF-LB considerations to achieve desirable microstructural and mechanical outcomes in WE43, supporting its potential use in biomedical applications.