Primary aluminum 7 percent silicon alloys (AA601{A356.0} or A356{357.0}) are widely used for structural or safety type applications that require higher and more-consistent mechanical properties. The properties of these alloys are determined primarily by three factors: melt composition, casting process and postcasting treatment. Alloy composition is an area that has been investigated considerably, in order to improve mechanical properties. As part of this work, a range of alloys with different iron and magnesium levels was cast at varying cooling rates. The castings were heat-treated and tensile tests were carried out. Mechanical properties are affected by all the variables investigated to varying extents; however, when ultimate tensile strength and elongation values are expressed as a quality index, an optimum magnesium level is found. Microstructural examination reveals that iron morphology is greatly affected by magnesium levels and heat treatment, and this plays a major part in the observed quality index peak. From the information generated, an optimum alloy composition can be specified for particular casting methods to maximize material properties.
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