The Corrosion Study on the Effect of Heat Treated Mg-Mn Alloy for Sacrificial Anode Cathodic Protection

摘要

The corrosion study of commercial High Potential Magnesium Anode on the effect of heat treatment process has improved the sacrificial anode criteria which are high open circuit potential (E_(oc)) and anode efficiency. Sacrificial anode with high potential and high anode efficiency is needed as it can protect large area of steel structure while providing efficiency protection. The commercial HPMA used in this study contains 0.74 wt. % Mn after chemical composition analysis using Spark Emission Spectrometer (SES). Heat treatment conducted on HPMA at three temperatures 150 °C, 250 °C and 350 °C for 8 hours soaking time and five cooling method selected which are air cooled, furnace cooled, water cooled, iced water cooled and iced saltwater cooled. The effect of heat treatment temperature and cooling method will be compared with non-heat treated HPMA and pure Mg. Heat treatment at low temperature (150 °C) and rapid cooling (iced saltwater) showed the highest value of E_(oc) (-1.6713 V_(SCE)) while high temperature (350 °C) and slow cooling (furnace cooled) provide the lowest E_(oc) (-1.4867 V_9SCE))-Corrosion rate determination using potentiostat show that sample heat treated at 150 °C and cooled in iced saltwater showed the lowest corrosion rate (21.87 MPY). Anode efficiency of HPMA improved from 48 % (non-heat treated) to 53 % (homogenized heat treated at 150°C) using ASTM-G97 method. XRD analysis showed that the a-Mn element which contributed in the HPMA alloy that leads to the performance as sacrificial anode. Microstructure analysis showed that dark particle (a-Mn) dissolved in the Mg matrix as homogenized heat treated at 150 °C. As the temperature increases to 250 °C and 350 °C, the number of dark particle increased and formed a larger particle which leads to the secondary protection and charge loss. This result supported by topographical analysis as the HPMA sample heat treated at high temperature shows severe pitting formation during anode efficiency test. The heat treatment at low temperature (150 °C) and rapid cooling (iced saltwater) shows the good sacrificial anode behavior with high E_(oc), low corrosion rate, high anode efficiency, and low pitting formation considered as the best heat treatment method to increase the performance of HPMA.