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.