Influence of anions, pH and coating on the localized corrosion behavior of AZ31 magnesium alloy in physiological environments

Abstract

Purpose

The purpose of this paper was to clarify the influence of H2PO4-, HCO3-, pH increase and phosphate coating on corrosion rate and localized corrosion tendency of AZ31 magnesium alloy.

Design/methodology/approach

The corrosion behavior of AZ31 magnesium alloy in physiological environments was investigated by hydrogen evolution collection measurements, electrochemical techniques and by use of a three-dimensional digital microscope.

Findings

H2PO4- and HCO3- have corrosion inhibition effects on AZ31 magnesium alloy in normal saline solutions. After immersing for 54 h, the surface undulations decrease from 100 to about 60 μm and 45 μm. The average corrosion rate decreased with increasing pH value. The localized corrosion tendency, however, increased significantly. CaHPO4·2H2O [dicalcium phosphate dehydrate (DCPD)] coating could decrease the initial i_corr of AZ31 substrate in Hank’s solution. With partial dissolution of the coating, localized corrosion was readily evident on the AZ31 substrate surface, and a large corrosion pit with depth of over 350 μm appeared. The combined effect of the presence of inhibited ions, the increase in pH during corrosion process and the DCPD coating caused the decrease in the average corrosion rate while enhancing the localized corrosion tendency, resulting in the observed localized attack.

Originality/value

The paper provides an essential insight into the localized corrosion mechanism of AZ31 magnesium alloy in physiological environments.

Citation

Hu, Q., Liu, J. and Huang, F. (2016), "Influence of anions, pH and coating on the localized corrosion behavior of AZ31 magnesium alloy in physiological environments", Anti-Corrosion Methods and Materials, Vol. 63 No. 4, pp. 301-307. https://doi.org/10.1108/ACMM-08-2014-1416