3. Material and methods
3.1. Specimen preparation
All specimen preparation experiments were carried out using ReaLizer SLM50 apparatus. It can produce objects of layer
Fig. 1 – SLM apparatus used for specimen production.
thickness as small as 20 mm using fiber laser beam (1070 nm) focused to 100 mm. Laser beam is directed to the surface of a new powder layer by mirrors which reflect the beam in two axes. Additional powder layers are applied and leveled by a mobile wiper which rotates on its axis to feed the material onto the building platform lowered by the layer thickness (Fig. 1). Experiments were conducted using AZ31 magnesium alloy spherical powder (TLS Technik & Spezialpulver GmbH) of particle size of 45–100 mm.
The produced specimens were rectangular, 5 mm 3 mm 3 mm, with layer thickness of 50 mm. The specimens had varying sets of parameters to enable assessment of their impact on the density of the melted material. Parameter sets were determined in line with the experimental designs described below.
The specimens were embedded to prepare metallographic specimens. The polished specimens were analyzed and photographed using Olympus OLS4000 confocal microscope (Fig. 2). The images were converted to monochromatic images and then the share of black pixels that corresponded to the pores was calculated and compared to the number of pixels for the entire analyzed image of sample cross-section, in order to determine specimen porosity.
Computed microtomograph Zeiss METROTOM 1500 was used in order to determine volume porosity in the material. The reconstruction was performed with resolution of 18.37 mm.
Prepared metalographic cross-sections were etched with 10% HNO3 solution in ethanol in order to reveal the microstructure. SEM analysis of specimens in z direction were performed, using Zeiss EVO MA25 microscope.