Synergistic effects of Ce and Mg on the microstructure and tensile properties of Al-7Si-0.3Mg-0.2Fe alloy

The effects of Ce and/or Mg on the microstructure and tensile properties of Al-Si-Mg-Fe alloys have been systematically investigated. Results showed that the separate addition of Mg or Ce could cause grain and eutectic Si refinement to some extent, whereas, the combined addition of Mg and Ce had a more appreciable grain refinement and excellent eutectic Si modification, modifying the eutectic Si morphology from plate-like to fibrous. The combined addition of Mg and Ce produced a large number of nanosized precipitates containing Ce and Mg within eutectic Si. These nanosized precipitates inhibited the Si growth and also the increase of constitutional undercooling were responsible for the excellent Si modification. Moreover, the combined addition of Mg and Ce significantly improved the strength and elongation due to grain refinement and eutectic Si modification. The ultimate tensile strength, yield strength and elongation reached 313 MPa, 227 MPa, 5.7%, respectively. Fractographic studies on alloys with a combined addition of Mg and Ce have revealed more dimples on tensile surface indicating a transition from brittle to ductile fracture than alloys with separate additions of Mg or Ce. These experimental findings provide a new feasible scheme for rare earth elements application in aluminum alloy casting production.