Abstract
The atmospheric corrosion progress of Mg alloys is traditionally tracked by determining mass loss of the samples after exposure. This method provides only an average corrosion rate over the exposure time and is destructive. The work presented introduces a new non-destructive method for real-time monitoring of atmospheric Mg alloy corrosion rates based on the evolved hydrogen gas. This is realized with an adaption of the gravimetric hydrogen collection method. The effect of temperature and atmospheric pressure variations during the experiment can be compensated and reliable atmospheric hydrogen evolution rates can be measured. The new technique was applied to monitor real-time atmospheric corrosion rates of Mg alloys AZ31 and AZ91 with different amounts of NaCl contamination. Comparing the results of the gravimetric hydrogen method with mass loss experiments reveals a good correlation of the consumed charge over the total exposure time, thus validating the new technique. Evidence for the contribution of O2 reduction reaction to cathodic processes on Mg alloy atmospheric corrosion is presented.
Highlights
Magnesium (Mg) alloys are attractive lightweight materials for automotive applications due to their high specific strength
Since different corrosion products form with different exposure conditions or different alloys, a direct comparison of different systems based on mass gain is difficult
As there is no gas present that could react to pressure fluctuations, the weight signal is independent of the atmospheric pressure
Summary
Magnesium (Mg) alloys are attractive lightweight materials for automotive applications due to their high specific strength. Mass loss measurements on Mg are carried out by removing the corrosion products after the exposure period, for example with a chromic acid solution.[5] The amount of metal loss is determined by weighing the sample before exposure and after the removal of the corrosion products. This method only provides an average corrosion. To obtain the dry mass gain value, the exposure needs to be interrupted by the drying process This characteristic is not suitable for a monitoring technique. Possible errors of the resistance method could be caused by a conductive electrolyte film that influences the measured resistance.[7]
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