1.0  Introduction:

 

An alloy is a mixture of metals or of a metal and another element. Aluminum based metal alloys are widely used for structural, aerospace,
marine and automobile applications for its light weight, high strength and low
production cost. The common alloying elements
are copper, magnesium, manganese, silicon, tin and zinc.

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The alloys can be divided
into two classes i.e. cast alloys and wrought alloys. The most important cast
aluminium alloy system is Al–Si,
where the high levels of silicon contribute to give good casting
characteristics. Silicon is the main alloying element. It imparts high fluidity
and low shrinkage, which result in good castability and weldability. These outstanding material characteristics are mainly
owing hard primary silicon particles crystallized
during the solidification. It is known that high amounts of crystallized
primary silicon particles are required to improve the wear resistance, finer
and granular primary silicon particles are moreover necessary to assure high strength
and ductility.

 

The
copper-free alloys are used for low to medium strength castings with good
corrosion resistance. The copper-bearing alloys are used for medium to high
strength castings, where corrosion resistance is not critical.

 

The wider applications of aluminum alloy
components are expected to achieve weight reduction of transport equipment such
as automobiles. Since hypereutectic Al-Si alloys exhibit high strength at
elevated temperatures, good wear resistance and a small thermal expansion
coefficient, they have been applied to compressor and engine components. The main use of aluminum-silicon alloys is
casting. Although some sheet or wire is made for welding and brazing, and some
of the piston alloys are extruded for forging stock. Because of their excellent
castability, it is possible to produce reliable castings, even in complex
shapes, in which the minimum mechanical properties obtained in poorly fed
sections are higher than in castings made from higher-strength but lower
castability alloys.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

2.0  Literature
Review:

 

Okayasu,
Ohkura, Takeuchi, Takasu, Ohfkuji and Shiraishi worked to find the best casting
process for the Al-Si-Cu alloy. They employed four casting procedures including
gravity casting (GC), cold-chamber die-casting (CD), twin rolled continuous
casting (TRC) and the Ohno continuous casting process (OCC). The twin-rolled
continuous casting (TRC) process is a process for making high quality casting
products, in which the cast sample is solidified with a high cooling rate using
chilled rollers. 1 OCC is a casting
technique proposed by Ohno, known as the Ohno continuous casting (OCC) process.
The OCC process is a unidirectional solidification method, and this casting
process provides phase control and texture control. The OCC process is
different from conventional continuous casting in that molten metal is poured
into a heated hollow mould, rather than one that is cooled. It appears that the
OCC-Al alloys have excellent tensile and fatigue properties because of their
unidirectional fine microstructure, low concentration of defects and uniformly
oriented lattice structure. 2 The microstructure
of GC and CD samples was formed mainly with coarse ?-Al phase and needle-shaped
Si based eutectic structures. In contrast, a fine round ? -Al phase and tiny
eutectic structures were observed for the TRC and OCC samples. Because of the
different material properties, the tensile and fatigue strength were altered.
Ultimate tensile stress and strain to failure for the TRC and OCC samples are
more than 40% higher than those for the CD and GC samples. Such an excellent
tensile property for TRC and OCC samples is caused by the fine round ? -Al
phase and tiny eutectic structures. As with the tensile properties, high
hardness and fatigue strength are obtained for the TRC and OCC samples. 3

 

Yoshiki Tsunekawa, Shinpei Suetsugu,
Masahiro Okumiya, Naoki Nishikawa, and Yoshikazu Genma worked on an increased
amounts of primary silicon particles which causes modified wear-resistance of
hypereutectic Al-Si-Cu alloys but leads to the poor strength and ductility.
With the application of ultrasonic vibration to molten Al-17Si-4Cu alloy, the
creation of hetero structure composed of hard primary silicon particles and
soft ?
-Al phase was attempted for rheo casting.
The tensile tests of T6 treated rheo-cast specimens with modified
sono-solidified slurry exhibited improved strength and 5% of elongation,
regardless of having more than 3 times higher amounts of primary silicon
particles. 4

 

Xiaowu ,
Fanrong and Hong investigated the
influences of pouring temperature and cooling rate on the microstructure
development and mechanical properties for casting Al-Si-Cu aluminum alloy. The
micro hardness increased with the increase of the pouring temperature due to
the reduced DAS. The ultimate tensile strengths of both metal and sand mould
casting alloys increased with increasing pouring temperatures, while the
elongation decreases with increasing pour-ing temperatures. 5

 

Dobrza?ski*, Borek and Maniara worked to show the
effect of solidification rate on microstructural features, hardness and micro
hardness of Al–Si–Cu alloys in as cast state and concluded that increasing the
solidification rate increases refines all microstructural features grain size.
Increasing the solidification rate have an impact on the hardness and micro
hardness of the aluminium cast alloys. 6

 

Canales, Carrera, Talamantes-Silva,
Valtierra and Colás* researched on a series of aluminum alloys with different
compositions and found out their mechanical properties. Heat treatment was
conducted on the specimen and the change in properties were observed. They
concluded that heat treating increases the strength of the material, but exerts
a negative effect in reducing its ductility. Also Silicon contributes to
increase the strength of the material; it was found that such an effect is
linked to the DAS, with the
highest effect when this last parameter falls within the 30 ?m to 40 ?m range.
7

 

Hailin Yang , Shouxun Ji and Zhongyun Fan
investigated the effect of solution and ageing heat treatment on the
microstructure and mechanical properties of the die-cast Al–9wt.%Si–3.5wt.%Cu
alloys containing 0.1–1.0wt.% Fe. Significant improvement in the mechanical
properties was achieved after the solution and ageing treatment of the die-cast
Al–Si–Cu alloy. Under the as-cast condition, the Al–Si–Cu alloys provided the
yield strength at a level of 140 MPa, the UTS at a level of 320 MPa, and the
elongation at a level of 3%. After solution-treated at 510 °C for 30 min and
aged at 170 °C for 24 h, the yield strength was increased to a level between
320 MPa and 350 MPa, the UTS to a level of 400 MPa, and the elongation to a
level between 2.5% and 4.1%, respectively. Al–Si–Cu alloys were not sensitive
to the Fe content in terms of mechanical properties under the as-cast
condition, although Fe could slightly increase the yield strength and slightly
decrease the ductility. 8

 

 

 

3.0  Objectives:

 

The research will
concentrate on the testing of mechanical properties of Aluminum-Silicon-Copper
alloy. The specific objectives of the research are:

 

a)     
To produce aluminum-silicon-copper alloy with different compositions.

b)     
To find out the mechanical properties of the alloy.

c)     
To compare the properties the alloys with different
compositions.

 

 

 

4.0  Methodology:

 

Aluminum, Silicon and Copper will be
melted in the furnace with predetermined compositions. Specimens of required
dimensions for the mechanical property tests will be formed by solidification
of the molten alloy. The composition of these alloy specimen will be
investigated for reference. Then mechanical tests i.e. Tensile test,
Compression test, Hardness test etc. will be carried out on these specimens to
investigate the properties of the alloy. These results will be compared to find
out the composition of Al-Si-Cu which provide the preferable mechanical
properties.