The Role of Humic Acid in the Corrosion of AZ31 Magnesium alloy

Abstract

Magnesium alloys used as sacrificial anodes can interact with humic acids (HAs) in soil and water environments. Therefore, these natural organic molecules can have an impact on the corrosion behaviour of magnesium materials. In this work, the aim was to investigate the effect of lignitic HA on the corrosion of AZ31 magnesium alloy in 3.5 % NaCl at different pH (5, 7 and 9). The results showed that HA increased the corrosion rate about four times at pH 7, while it weakly decreased the corrosion rate at pH 5 and 9. The acceleration of corrosion is probably related to the depletion of Mg 2+ ions by forming complexes with HA instead of producing Mg(OH)2. The increase in corrosion resistance may be related to the reduced stability of the complexes and adsorption on the AZ31 alloy surface at pH 5 and 9. Surface analysis suggested that the presence of HA promotes the formation of Mg(OH)2 nanoparticles.

CORROSION BEHAVIOUR OF AZ31 ALLOY IN AN ALKALINE ENVIRONMENT OF 0.1 m nacl in the presence of lignitic humic acid

“…It can be assumed that the humic acid formed complexes with Mg 2+ ions and this resulted in the inability to form a sufficiently semi-protective Mg(OH)2 layer. These findings are consistent with the literature [10]. The AZ31 alloy samples after corrosion in NaCl were characterized using SEM-EDS analysis, see Figure 2.…”

“…The results showed that humic acid contributes to the depletion of magnesium ions by forming complexes and thus to the increase in corrosion rate. The study also suggested that the presence of humic acid could promote the formation of magnesium hydroxide nanoparticles on the surface of AZ31 alloy [10]. There are also studies on the effect of humic acids on the corrosion behavior of other metallic materials such as low carbon steel [11].…”

Corrosion behaviour of AZ31 magnesium alloy in saline containing glucose at different concentrations

“…AZ31 magnesium alloy samples (20 × 20 × 6 mm) were used for corrosion tests. The alloy chemical composition was determined using Glow-Discharge Optical Emission Spectroscopy (GDOES); 3.60 % Al, 1.34 % Zn, 0.28 Mn, 0.03 Si, 0.002 Fe and 0.01 Sn [7]. The samples of AZ31 alloy were ground using 320 and 1200 SiC grit abrasive papers, washed in distilled water and isopropyl alcohol and then dried by hot air.…”

Influence of humic acid on corrosion of low carbon steel in neutral aqueous solution containing chlorides

“…The authors found that there was a deterioration of corrosion process during short-term measurements, but longer-term tests suggested that there may be an improvement in corrosion resistance. In another paper, Doskočil et al investigated the effect of humic acid in 3.5% NaCl on the corrosion of magnesium alloy AZ31 [9]. They observed that the corrosion rate slowed down slightly at pH 5 and 9, while corrosion accelerated at pH 7.…”