Mechanical properties of Al-11% Si casting alloys containing trace Be and Sr

To learn the effects of Be and Sr contents on improving the morphologies of iron intermetallic compound and eutectic silicon particles, the mechanical properties of Al-11%Si casting alloys were investigated. The variations of series alloys were studied by optical microscopy, an electron probe X-ray microanalyzer, a conductivity meter, an image analyzer, a hardness tester and a tensile machine. The mechanical properties of the Al-11%Si casting alloys have been evaluated as a function of the number, magnitude and morphology of the iron-rich phase and silicon particles. The addition of Be is beneficial for the transformation of the needle-shaped iron-rich phase into the Chinese-script shape and the refinement of silicon particles. With the addition of Sr, the most brittle flake eutectic silicon may be modified to be fiberlike (spherelike) and the iron-rich phase may also be refined. The alloy's strength and ductility with the addition of Sr are superior to those with the addition of Be. The ductility may be improved most significantly as both the Sr and Be contents are increased.