Mechanical Properties and Corrosion Resistance of La2O3/A356 Composites Fabricated by Ultrasonic-Assisted Casting

Mechanical properties and corrosion resistance of La2O3/A356 composites with different contents of La2O3 were investigated by optical microscopy, X-ray diffractometry, scanning electron microscopy, electrochemical tests, and immersion corrosion tests. The results show that the addition of La2O3 refined the alpha-Al phase of the A356 matrix, and the long stripe-like Si phase and beta-Al5FeSi phase were transformed into short rod-like forms. The La2O3/A356 composites with 1.0 wt.% La2O3 exhibited the most optimal mechanical properties and corrosion resistance. The yield strength, ultimate tensile strength, and elongation of La2O3/A356 composites with 1.0 wt.% La2O3 were higher than those of the matrix. The results of electrochemical experiments and the immersion corrosion test show that the corrosion potential of La2O3/A356 composites with 1.0 wt.% La2O3 was 72 mV higher than that of the matrix, the corrosion current density was 84.8% lower than that of the matrix, and the impedance Z was improved by 59.1% compared to the matrix. The addition of La2O3 improved the mechanical properties of the A356 matrix by refining the grains, inhibiting the nucleation of eutectic Si, and promoting the twinning growth mechanism. Moreover, the effect of La2O3 on the micro-galvanic corrosion behavior of A356 was discussed.