Preparation of HVAF prepared Al-based amorphous coating and its corrosion behavior characterization

  Objectives  To improve corrosion resistance of 2024 aluminum alloy, this paper investigates the preparation of an advanced coating and its corrosion behaviors.

  Methods  2024 aluminum alloy was coated with an Al-based amorphous alloy coating using high-velocity air fuel spraying(HVAF)technology at high spraying speed. The composition, microstructure and corrosion morphology of the coating and matrix were analyzed using an X-Ray diffractometer, transmission electron microscope and scanning electron microscope, and potentiodynamic polarization plots and EIS curves in 3.5% NaCl solution were measured.

  Results  The results indicate that the cooling rate of the melt particles is higher than the critical cooling rate of the amorphous alloy due to the high spraying speed, which greatly increases the amorphous content of the coating. Meanwhile, the high spraying speed effectively reduces the porosity of the coating. The amorphous content of the coating reached 81.3% and the porosity of the coating was low at 0.35%. Moreover, the corrosion resistance of the Al-based amorphous alloy coating was obviously superior to that of the 2024 aluminum alloy with a lower corrosion current density(8×10^-6 A/cm²)and a higher pitting potential(-0.30 V). The impedance value of the coating was four times that of the 2024 aluminum alloy substrate. The corrosion mechanism of the Al-based amorphous alloy coating was homogeneous corrosion, while that of the 2024 aluminum alloy was pitting.

  Conclusions  The high amorphous content and low porosity of the Al-based amorphous alloy coating contribute to its improved corrosion resistance.