Improvement in corrosion resistance of magnesium weld by addition of carbon nanotubes

The corrosion resistance of base metal, laser-arc hybrid welded AZ31B magnesium alloys with and without addition of carbon nanotubes (CNTs) was compared. The corrosion behaviors and the underlying improvement mechanism of CNTs were systematically investigated. The introduction of CNTs effectively refined the grains, weakened the texture and enhanced the microstructure homogeneity of the weld, which contributed to the enhancement of corrosion resistance. Specifically, the corrosion rates of hydrogen evolution and weight loss of weld decreased by >30% after the addition of CNTs, and the corrosion products were denser due to the formation of Al₂O₃ passive film. The corrosion current density and polarization resistance of weld with addition of CNTs were 1.220 µA/cm² and 7155 Ω·cm², respectively, in contrast to 2.480 µA/cm² and approximately 269.5 Ω·cm² for the weld without CNTs. Besides, the content of precipitates in the weld increased from 0.60% to 1.76% after the addition of CNTs, which can release Al³⁺ ions, promoting the formation of a dense Al₂O₃ film that serves to protect the metal matrix from further degradation.