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Al- Si alloy for automotive applications

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الكلية كلية الهندسة/المسيب     القسم هندسة السيارات     المرحلة 2
أستاذ المادة جعفر هادي عبود المياح       01/11/2018 21:41:59
1.1 AL-SI BASED CASTING ALLOYS
1.1.1 Background
Due to economic and environmental requirements, it is becoming increasingly important to
reduce vehicle weight. For such an objective, Al-Si cast alloys have been widely employed to
produce automotive components working at ambient and fairly high temperature (up to 200
?C) due to excellent characteristics such as low cost manufacturing, excellent castability, high
specific strength and recyclability [1, 2]. Cu and Mg are commonly added to improve the
strength at room and elevated temperatures and enable the possibility of heat treatment [3].
The microstructure of these casting alloys contains ?-Al dendrites as the main constituent,
which is decorated with eutectic Si particles and many intermetallic phases such as Al2Cu,
Mg2Si, Fe-bearing phases etc. The size, morphology and distribution of microstructural
features govern the mechanical properties of theses alloys [4]. It is well-known that a refined
microstructure results in improved tensile properties. The refinement of microstructure can
be achieved through high cooling rate or chemical modification. Usage of Al-Si-Cu-Mg alloys
at temperature above 230 ?C is however limited due to coarsening of Si particles and
dissolution of Cu- and Mg-bearing phases.
1.1.2 Alloying elements
Si is the main and most important alloying element of Al-Si cast alloy. In hypoeutectic Al-Si
alloy, the Si content normally varies from 5 to 12 wt. %. Si is primarily responsible for socalled
“good castability”; i.e., the ability to readily fill dies and to solidify castings with no hot
tearing or hot cracking issues. The more Si an alloy contains, the lower is its thermal
expansion coefficient. Si is a very hard phase, thus it contributes significantly to an alloy’s
wear resistance. Si combines with other elements to improve an alloy’s strength and to make
alloys heat treatable.

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