“Influence of Si, Sb and Sr Additions on the Microstructure ...

[E my g Chapter 4: Results <strong>and</strong> Djscussion
4.4 TENSILE PROPERTIES
The alloying additions, apart from introducing various intermetallics <strong>and</strong>
refining the grain size, refines also the Mg11Al1; intermetallics in some cases (like <strong>Sr</strong>
addition). These microstructural variations influence the tensile properties <strong>of</strong> AZ91
alloy. Hence, the tensile properties <strong>of</strong> AZ91 alloy with <strong>and</strong> without additions were
evaluated, compared <strong>and</strong> presented in this section. Tensile samples were prepared in
accordance with ASTM E8 st<strong>and</strong>ard <strong>and</strong> the tests were carried out at room as well as
high temperatures (up to 200°C for base alloy <strong>and</strong> at 1509C for all remaining alloys).
Five samples were tested for each alloy <strong>and</strong> the average value was reported.
Extensometer was used to get the % elongation during room temperature testing but
for high temperature tests, the values were manually calculated from the markings on
the sample (25mm gauge length was used). Fractography studies were also carried out
to identify the micro-fracture mechanism.
4.4.1 AZ91 Alloy
Figure 4.37 presents the ultimate tensile strength (UTS), yield strength (YS)
<strong>and</strong> percentage <strong>of</strong> elongation (%E) <strong>of</strong> AZ91 alloy measured from the tensile test
carried out at different testing temperatures (RT, 100, 150, 200°C). The tensile
properties obtained in the present investigation are inline with the st<strong>and</strong>ard values
reported in the Materials Science H<strong>and</strong> Book [296] <strong>and</strong> published by Intemational
Magnesium Association (IMA), Canada [297]. In fact, the tensile properties obtained
in the present study are higher than many published values in literature [41, 42, 48]. In
general, the mechanical properties <strong>of</strong> AZ9lalloy reported in literature are scatter in
nature mainly due to the difference in the casting process variables, which alter the
microstructural features like grain size, eutectic volume fraction, porosity <strong>and</strong> etc
[298, 299]. Moreover, properties variation within casting is also noticed by many
researchers [43, 155, 300-304]. E. Aghion et al [155] have reported that the tensile
properties <strong>of</strong> die cast AZ91 alloy are highly sensitive to wall thickness. Considerable
change in UTS, YS <strong>and</strong> %E is noticed with samples tested from different location
along the wall thickness <strong>of</strong> casting. Yang et al [43] have also reported the same in
gravity cast AZ91 alloy.
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