Microstructure and mechanical properties of Al-7Si-0.7Mg alloy formed with an addition of (Pr+Ce)

Abstract Effects of (Pr+Ce) addition on the Al-7Si-0.7Mg alloy were investigated by optical microscope (OM), energy diffraction spectrum (EDS), X-ray diffraction (XRD) and tensile tests. The results showed that the Al-7Si-0.7Mg alloy was modified with (Pr+Ce) addition. The needle-like eutectic silicon phase developed into rose form and the crystalline grains decreased in size and showed a high degree of spheroidization. When the amount of the (Pr+Ce) addition reached 0.6 wt.%, the mean diameter was 31.8 μm (refined by 50%). The aspect ratio decreased to 1.35, and the tensile strength and ductility reached 192.4 MPa and 2.18%, respectively. At higher levels of addition, over-modification occurred, as indicated by increased grain size and reduced mechanical properties. The poisoning effect of the (Pr+Ce) addition on eutectic silicon and the constitutional supercooling caused by the (Pr+Ce) addition were the major causes of alloy modification, grain refinement, and the improvement of mechanical properties.

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