Civil Engineering Reference
In-Depth Information
Fig. 8.14
Sample mounting
locations and orientations
8.3 Microstructure Analysis Under Tensile Loading
Bulk properties such as strength or ductility of a metal can be empirically obtained
from material testing. However, to fully understand these observed macro-prop-
erties, the underlying material microstructure must be examined. Therefore, this
section examines the microstructure of Mg AZ31B sheet metal in the as-received
condition and under various EAF conditions. As the microstructure may vary in
different orientations or spatially due to processing, several locations and orienta-
tions on the ASTM tensile samples were examined. The possible locations and ori-
entations examined are shown in Fig.
8.14
where L1 to L4 represent the possible
mounting locations (select areas were chosen depending on the desired compari-
sons) and 1-3 represent the different orientations at a given location.
Direction 1 is oriented such that the micrograph is showing a plane perpen-
dicular to the rolling direction where the roll direction is parallel to the specimen
length axis. Direction 2 is oriented to provide a micrograph that examines a plane
parallel to the rolling direction. Direction 3 is oriented orthogonal to direction 1
and direction 2 such that the micrograph is in plane with the top surface of the
sheet. In order to specify these orientations during mounting, different color speci-
men clips were used. Thus, in the below results which label the sample, a capi-
tal letter “R” denotes orientation 1, “B” or “K” denotes orientation 2, “NONE”
denotes orientation 3, and additional letters and numbers represent the image
number. As an example, “S1Rb2” means Sample 1 showing orientation 1 and the
image number is b2.
8.3.1 As-Received Material Microstructure
The as-received material was first examined to evaluate grain size and to under-
stand the distribution of the grain size measurements. To quantify the grain size,
approximately 100 grains were each fit by an ellipse for each micrograph. From
the ellipse geometry, the area of each measured grain could be calculated. Using
the calculated area, the equivalent circular grain diameter was determined and this
value is presented to represent the grain size in the micrographs.
