Fabrication and anodising of aluminium matrix composite made from flaky aluminium powder and short fibre Saffil™ alumina
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Date
2006
Authors
Derman, Mohd Nazree
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Abstract
A study of fabrication and anodising on aluminium matrix composites (AMC) made from
flaky aluminium powder and short fibre alumina Saffil™ was carried out. AMC fabrication
by powder metallurgy methods (PM) using dry mixing and sintered in nitrogen was
studied to determine the best sintering time and optimum percentage of Saffil™ alumina
short fibres content. Sulphuric acid anodising process was performed and the objective
is to obtain suitable parameters of sulphuric acid concentration, anodising voltage and
anodising time. Characterisation on AMC included anodised also involved corrosion and
wear test. The optimum Saffil™ alumina short fibre contents (0 to wt 25%) was
determined by microstructure, density and porosity test, tensile strength, microhardness
test, X-ray diffraction (XRD) analysis and coefficient of thermal expansion (CTE)
analysis. The study of anodising process was carried out with various sulphuric acid
concentrations (from 0 to 20% volume), anodising voltage (10 V to 20 V) and anodising
time (from 0 to 60 minutes) at room temperature. Corrosion tests was also done in 3.5
wt% sodium chloride (NaCl) solution using electrochemical polarisation measurement
based on ASTM G5 (1999), whereas pin-on-disk test was used for wear testing. From
the research, AMC from flaky Al powders and Saffil™ alumina short fibre was
successfully produced with good properties using dry mixing method and sintered in
nitrogen atmosphere for 7 hours. AMC reinforced with 15 wt% Saffil™ alumina short fibre
was selected because it showed optimum properties such as relatively uniform
distribution of fibres in Al matrix, relatively low density, 2.61 g cm-3 and low porosity
1.33%. The tensile strength value for AMC reinforced with 15 wt% was 105.04 MPa,
elastic modulus 8.38 GPa and microhardness HVN 84.02, CTE 16.41 x 10-6 K-1 and
small linear changes with no new phases as shown by XRD results. Anodising voltage of
15 V and 15 vol% H2SO4 in anodising time of 60 minutes were suitable parameters for
sulphuric acid anodising of this AMC. The anodising can reduce corrosion reaction rate
on Al and AMC with decreasing corrosion current density. Anodising also reduced 59%
and 13% wear coefficient of Al and AMC, respectively. Generally, the results showed
that good properties of AMC can be fabricated from flaky Al powders reinforced with
Saffil alumina shorts fibre by PM methods. AMC reinforced with 15% alumina shorts
fibre Saffil™ was the best AMC. The AMC showed higher corrosion rate but lower wear
rate compared to the Al samples. From the research, it was found that H2SO4 anodising
was able to give good coating to AMC. The anodised AMC samples showed better
corrosion resistance and wear resistance.
Description
PhD
Keywords
Materials and Mineral Resources Engineering , Aluminium matrix composite , Flaky aluminium powder , Saffil™ alumina