Srinivasan, A; Dr.Pillai, U T S(National Institute for Interdisciplinary Science and Technology, April , 2008)
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Abstract:
All the exciting work on developing new and better alloys has led older alloys,
such as AZ9l , being abandoned by researchers. lt is believed that the full potential of
AZ9l in automotive design has not been realized. Whatever works have been carried
out on AZ9lalloy to improve its mechanical properties are insufficient in terms of its
potential usage in auto industries. Due to the fact that AZ91 offers high room
temperature mechanical properties and good castability, still this alloy is a primary choice for the auto component manufactures. Small improvement in its creep
properties will have a huge impact in the transportation industries. Hence, in the
present work, “Influence of Si, Sb and Sr Additions on the Microstructure,
Mechanical Properties and Corrosion Behavior of AZ91 Magnesium Alloy”, an
attempt has been made to improve the creep properties of AZ9l alloy through minor
alloying elemental additions and to understand its strengthening mechanisms. The
effect of alloying additions on the ageing and tensile properties of AZ9l is also
studied. In addition to that, role of various intermetallics formed due to the alloying
additions on the corrosion properties of AZ9l alloy is investigated.
Balasubramani, N; Dr.Pillai, U T S(National Institute for Interdisciplinary Science and Technology (CSIR), 2009)
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Abstract:
MAGNESIUM ALLOYS have strong potential for weight reduction in a wide
range of technical applications because of their low density compared to other structural
metallic materials. Therefore, an extensive growth of magnesium alloys usage in the
automobile sector is expected in the coming years to enhance the fuel efficiency through
mass reduction. The drawback associated with the use of commercially cheaper Mg-Al
based alloys, such as AZ91, AM60 and AM50 are their inferior creep properties above
100ºC due to the presence of discontinuous Mg17A112 phases at the grain boundaries.
Although rare earth-based magnesium alloys show better mechanical properties, it is not
economically viable to use these alloys in auto industries. Recently, many new Mg-Al
based alloy systems have been developed for high temperature applications, which do not
contain the Mg17Al12 phase. It has been proved that the addition of a high percentage of
zinc (which depends upon the percentage of Al) to binary Mg-Al alloys also ensures the
complete removal of the Mg17Al12 phase and hence exhibits superior high temperature
properties.ZA84 alloy is one such system, which has 8%Zn in it (Mg-8Zn-4Al-0.2Mn, all
are in wt %) and shows superior creep resistance compared to AZ and AM series alloys.
These alloys are mostly used in die casting industries. However, there are certain large
and heavy components, made up of this alloy by sand castings that show lower
mechanical properties because of their coarse microstructure. Moreover, further
improvement in their high temperature behaviour through microstructural modification is
also an essential task to make this alloy suitable for the replacement of high strength
aluminium alloys used in automobile industry. Grain refinement is an effective way to
improve the tensile behaviour of engineering alloys. In fact, grain refinement of Mg-Al
based alloys is well documented in literature. However, there is no grain refiner
commercially available in the market for Mg-Al alloys. It is also reported in the literature
that the microstructure of AZ91 alloy is modified through the minor elemental additions
such as Sb, Si, Sr, Ca, etc., which enhance its high temperature properties because of the formation of new stable intermetallics. The same strategy can be used with the ZA84
alloy system to improve its high temperature properties further without sacrificing the
other properties. The primary objective of the present research work, “Studies on
grain refinement and alloying additions on the microstructure and
mechanical properties of Mg-8Zn-4Al alloy” is twofold:
1. To investigate the role of individual and combined additions of Sb and Ca on
the microstructure and mechanical properties of ZA84 alloy.
2. To synthesis a novel Mg-1wt%Al4C3 master alloy for grain refinement of
ZA84 alloy and investigate its effects on mechanical properties.