Material and Experiment

Material

The material used for this investigation is extruded ZK60-T5 magnesium. The 150 mm radius cylindrical bar was acquired from SMW Engineering, Russia as 1000 mm long bar. The chemical composition of the alloy is listed in Table 1. The microstructure of the material was analyzed by preparing metallurgical samples that were polished with abrastive papers having grit sizes of 240, 320, 400 and 600. After that, the samples were etched. The etchant was prepared using 5 g picric acid, 5 ml acetic acid, 10 ml distilled water and 100 ml ethanol. Micrographic analysis of the etched samples was performed using Olympus DSX-510 digital microscope. Finally, texture analysis was carried out using Bruker D8 Discover X-ray diffractometer on the material.

Mechanical Tests

The material was cut into rectangular blanks with their longitudinal direction parallel to the extrusion direction. Then, they were turned into cylinders with a diameter of 12 mm. Two unnotched specimens (Fig. 1a) were machined from the same blanks used for the notched specimens. These unnotched specimens are used to obtain the stress-strain curves of the material. After that, U and V notches with different sizes were introduced in the center of the specimens. The notches were machined with a depth of 3 mm. Four U-notch geometries with notch root radii of 1.5, 3, 4, 5 and 6 mm were considered. For V notch geometry, two notch root radii and three notch opening angles were considered: 0.4 and 0.8 mm, and 35, 60 and 90, respectively. Representative geometries for one U and one V notch specimens are shown in Figs. 1b and 1c. Three duplicates were tested for each distinct geometry. The unnotched and the notched specimens were tested at the same loading rate, i.e., 2 mm/min. All tests were performed using Instron 5569 frame having a loadcell capacity of 50 kN.

Fracture Surface Analysis

Optical (OM) and scanning electron microscopes (SEM) were used to analyze the fracture surfaces of the samples. The morphology of fracture surface obtained from the tested specimens was evaluated using a Olympus DSX-CB microscope, which has a capability to perform analysis and measurement of 3D surfaces. The used field emission scanning electron microscope (FE-SEM) is FEI, Quanta FEG 250, Czech Republic.