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

2.1 INTRODUCTION
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The weight <strong>of</strong> the average family car has increased by 20% over the last 20
years [51]. Most <strong>of</strong> the increased weight is a result <strong>of</strong> increased average engine size
<strong>and</strong> the additions <strong>of</strong> safety features. On the other h<strong>and</strong>, customer’s awareness <strong>of</strong> fuel
efficiency has been made more acute by increasing fuel prices <strong>and</strong> the popularity <strong>of</strong>
environmental issues. So, weight reduction is an imperative task for automobile
producers. The attractive benefit <strong>of</strong> reduction in automobile weight can be seen in
temis <strong>of</strong> improved fuel efficiency as shown in Figure 2.1 [52]. “Concept cars”
produced in recent years have been lightweight, for example, the Ford P2000, which
weighs only 544.3 Kg [53]. The weight reductions have been made possible by the
replacement <strong>of</strong> steel by light metal alloys, usually aluminum or magnesium. ln
production vehicles, the weight is saved through the use <strong>of</strong> lightweight metals, which
have reduced the weight <strong>of</strong> cars by 10% since 1978, without compromising safety
[54]. Earlier, aluminum alloys replaced most <strong>of</strong> steel or cast iron components in
automobiles. But at this moment, the major aim <strong>and</strong> task <strong>of</strong> the researchers is to find
suitable material, which is more efficient than aluminum so as to reduce the weight <strong>of</strong>
automobile further. Magnesium <strong>and</strong> its alloys are one such promising material, whose
lightweight advantage could be used for the above said purpose.
Magnesium, with a density <strong>of</strong> 1.7 g/cc is the lightest <strong>of</strong> the structural
materials. It is two third <strong>of</strong> its counterpart aluminum density (2.7 g/cc) <strong>and</strong> one third
<strong>of</strong> steel density (7 g/cc). So, it has high specific strength properties over aluminum
alloys. However, the total annual world consumption <strong>of</strong> magnesium at around 250
thous<strong>and</strong> tones is a fraction <strong>of</strong> the 20 million tones <strong>of</strong> aluminum used. Both metals
were discovered in the early 19“ century <strong>and</strong> industrial refining processes for each
metal were announced in 1886. So, the lower usage <strong>of</strong> magnesium is due to different
complex <strong>of</strong> factors. However, developments in magnesium refining <strong>and</strong> processing
technology have coincided with new dem<strong>and</strong>s from many industries for high
precision light-weight die-castings. Now the use <strong>of</strong> magnesium is growing at a faster
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