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

T 1 H Cghapter4: Results <strong>and</strong> Discussion
precipitates using XRD. In the present study no such peaks corresponding to Mg3<strong>Sb</strong>;
precipitate is observed in XRD studies. On the other h<strong>and</strong>, the EDS analysis carried
out on the Mg;;<strong>Si</strong> particle indicate the presence <strong>of</strong> <strong>Sb</strong> in it as shown in Figure 4.21. In
order to have more information on the distribution <strong>of</strong> <strong>Sb</strong> over the Mg2<strong>Si</strong> intermetallic,
line scan across the particle <strong>and</strong> X-ray mapping was also carried out <strong>and</strong> given in
Figures 4.22 <strong>and</strong> 4.23 respectively. These studies confirm no <strong>Sb</strong> concentration in the
Mg;<strong>Si</strong> particles, rather distributed evenly throughout the Mg2<strong>Si</strong> intermetallic.
Elements like Ca. P <strong>and</strong> <strong>Sb</strong> are normally added to Al-<strong>Si</strong> alloys to modify the
eutectic <strong>and</strong> primary <strong>Si</strong> particles. <strong>Sr</strong> is also a well-known modifier for <strong>Si</strong> in
hypoeutectic Al-<strong>Si</strong> alloys [268, 269]. Based on this, it is believed that <strong>Sr</strong> can also
change the morphology <strong>of</strong> Mg;<strong>Si</strong> intermetallic. However, studies on <strong>Sr</strong> modification
<strong>of</strong> Mg2<strong>Si</strong> intermetallic in Mg alloys is not reported in literature. In the present study,
<strong>Sr</strong> modification <strong>of</strong> Mg2<strong>Si</strong> intermetallic in AZ9l alloy is carried out <strong>and</strong> found that <strong>Sr</strong>
changes the morphology <strong>of</strong> Mg;<strong>Si</strong>. <strong>Si</strong>milar to <strong>Sb</strong> modified alloy the XRD pattem
taken on the <strong>Sr</strong> modified alloy does not show any peaks for <strong>Sr</strong> containing component.
However, EDS spectrum taken at the Mg2<strong>Si</strong> precipitates shown in Figure 4.24
indicates the presence <strong>of</strong> <strong>Sr</strong> in it. X-ray mapping <strong>of</strong> the <strong>Sr</strong> modified Mg;<strong>Si</strong>
intermetallic (Figure 4.25) also indicates the distribution <strong>of</strong> <strong>Sr</strong> in Mg;<strong>Si</strong> intermetallic
IS even.
From these results, it is more logical to conclude that both the <strong>Sb</strong> <strong>and</strong> <strong>Sr</strong>
addition restrict the growth <strong>of</strong> Mg2<strong>Si</strong> intermetallic during solidification <strong>and</strong> change
the morphology rather than act as a nucleant. Uneven size <strong>and</strong> shape <strong>of</strong> the modified
Mg;<strong>Si</strong> particles are also support this modification mechanism. However, more
rigorous TEM studied are needed to confirm the modification mechanism, which is
included in the future course <strong>of</strong> work.
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