Effects of La-Ce addition on microstructure and mechanical properties of Al-18Si-4Cu-0.5Mg alloy

The microstructural evolution and mechanical properties of Al-18Si-4Cu-0.5Mg alloy modified by the addition of La-Ce rare earth elements through OM, SEM, EPMA and tensile tests were investigated. The results of OM and SEM analyses indicated that primary Si particles were significantly refined from coarse block-like and irregular polygonal shapes into fine flaky shapes, while eutectic Si particles were modified from coarse and needle-like into fine and rod-or coral-like shapes with increase of La-Ce addition. The alloy exhibited the minimum primary Si particle size and the best mechanical properties with the addition of 0.3 wt.% La-Ce. The average particle size decreased from 61 to 28 mu m, the ultimate tensile strength increased from 222 to 242 MPa and the elongation increased from 3.2% to 6.3%. In addition, modification mechanisms and fracture modes were explored by the means of SEM and EPMA.