Effect of La Addition Amounts on Microstructure Refinement and Properties of Recycling Al-9Si-1Fe Alloy

The recycling Al-9Si-1Fe-xLa alloys （x=0, 0.1%, 0.2%, 0.3%, 0.4% and 0.5%, mass fraction/%） were prepared by melting industrial pure aluminum together with Al-50Fe, Al-20Si, and Al-20La master alloys, followed by ultrasonic treatment at 2 000 W power before casting. The effects of La addition amounts on the microstructure, mechanical properties and tribological properties of the alloys were studied. The results show that with increasing the addition amount of La, the secondary dendrite arm spacing of α-Al, the aspect ratio of eutectic silicon, and the length of Fe-rich intermetallic compounds in the alloy all decreased first and then increased; when the La addition amount （mass fraction） was 0.3%, they reached the minimum values of 5.4 μm, 1.00 and 4.5 μm respectively, and the microstructure refinement effect was the best at this addition level. As the La addition amount increased, the hardness of the alloys was improved, the tensile strength and elongation after fracture first increased and then decreased, and the average friction coefficient first decreased then increased. When the addition amount of La increased from 0 to 0.3%, the wear rate decreased from 1.37×10⁻² mm³·N⁻¹·m⁻¹ to 0.85×10⁻² mm³·N⁻¹·m⁻¹, with a reduction of 38%. When the La addition amount was 0.3%, the tensile strength and elongation after fracture reached the maximum values of 224 MPa and 2.28%, and the average friction coefficient was the lowest.