Quantitative evaluation of initial galvanic corrosion behavior of CNTs reinforced Mg–Al alloy

The macroscopic corrosion phenomenon of the CNTs reinforced Mg composites remarkably occurred in the moist environment, due to a large potential of the galvanic cells formed between α-Mg matrix and CNTs. Therefore, it is necessary to reduce the potential difference at their interfaces in order to obstruct the galvanic corrosion phenomenon. In this study, AZ61B alloy composites reinforced with CNTs (CNT/AZ61B) were fabricated by powder metallurgy method, and their potential differences between CNTs and the α-Mg matrix were reduced by concentration of Al atoms around CNTs via heat treatment. The potential distribution around CNTs was measured by using scanning Kelvin probe force microscopy (SKPFM). Heat treatment of CNT/AZ61B composites at 823 K for 10 h caused the obvious concentration of Al atoms around CNTs, and resulted in the remarkable decrease of the potential difference at the interface between the α-Mg matrix and CNTs. Additionally, the salt water immersion test results indicated that the corrosion rate of CNTs/AZ61B composite materials after heat treatment was obviously reduced to less than about 30% of the non-treated composite material. Thus, the changes of α-Mg matrix potential by concentrating Al atoms around CNTs was effective to improve initial galvanic corrosion resistance of CNTs reinforced Mg composites.

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► New materials design was proposed to improve the corrosion resistance of Mg alloys.
► Heat treatment was applied to CNT/AZ61B composites.
► After heat treatment, solid-soluted Al atoms were obviously concentrated around CNTs.
► The potential difference between Mg and CNTs was decreased by Al concentration.
► The corrosion rate of after heat treatment was reduced than non-treated material.