Improved mechanical and frictional properties of hypereutectic Al-Si alloy by modifying Si phase with La addition

Hypereutectic Al-Si alloys play an important role in the automotive industry and wear-resistance field. In this study, B390 hypereutectic Al-Si alloys with different La additions (0, 0.2, 0.4, 0.6 wt%) are solidified under permanent magnet stirring. The beneficial effects of La addition on the B390 alloy are investigated by XRD, DSC, SEM, EPMA, hardness tester, tensile tester and wear tester. Experimental results indicate that as the La addition increases from 0 to 0.4 wt%, the Si phase evolves from coarse needle-like to fine coral-like particles, and the mean size decreases from 18.6 mu m to 4.7 mu m. Moreover, the introduction of La to B390 alloy would result in an enhancement in tensile strength from 115.7 MPa to 162.1 MPa, and an increase in the Rockwell hardness from 58.5HRB to 66.4HRB. In addition, the average friction coefficient of the alloy decreases from 0.55 to 0.48 with the increasing La addition from 0 to 0.4 wt%, indicating an obvious improvement in frictional properties. It is noted that adding 0.6 wt%La cannot further improve the Si phase or enhance its properties of the B390 alloy in comparison to the addition of 0.4 wt%La. These results confirm that a suitable La addition is feasible and economical to improve materials performance of hypereutectic Al-Si alloy.