EFFECT OF IRON ON THE MICROSTRUCTURE AND MECHANICAL PROPERTIES OF Al-Si ALLOYS

摘要

The effect of iron content on the microstructure and mechanical properties of Al-Si alloy has been studied by optical microscopy, universal material testing machine and x-ray diffraction (XRD). The crystal structure and morphology of iron-phases and the distribution of iron element have been observed by scanning electron microscope (SEM) and energy-dispersive x-ray analysis (EDAX). It is shown that the mechanical properties of castings gradually decrease with iron content, then rapidly drop when iron content is greater than approximately 1.0wt%. This is because the iron-phase in castings changes from Chinese-character shape a-phase to needle-shape β -phase. In order to reduce the harmful effect of iron-phase, Mn was added into the iron contained melts at a fixed ratio of Mn/Fe, which will promote the transformation of iron-phase from needle-shaped to Chinese-character shape. The related mechanism about the effect of Fe and Mn on Al-Si alloy has been analyzed.