Influence of inorganic acid pickling on the corrosion resistance of magnesium alloy AZ31 sheet

Abstract

Surface contaminants as a result of thermo-mechanical processing of magnesium alloys, e.g. sheet rolling, can have a negative effect on the corrosion resistance of magnesium alloys. Especially contaminants such as Fe, Ni and Cu, left on the surface of magnesium alloys result in the formation of micro-galvanic couples and can therefore increase corrosion attack on these alloys. Due to this influence they should be removed to obtain good corrosion resistance. In this study, the effect of inorganic acid pickling on the corrosion behaviour of a commercial AZ31 magnesium alloy sheet was investigated. Sulphuric, nitric and phosphoric acids of different concentrations were used to clean the alloy for various * Manuscript Click here to view linked References 2 pickling times. The surface morphology, composition and phases were elucidated using scanning electron microscopy, X-ray fluorescence analysis, spark discharge-optical emission spectroscopy, energy dispersive X-ray spectroscopy and infrared spectroscopy. The effect of surface cleaning on the corrosion properties was studied using salt spray test and electrochemical impedance spectroscopy. The experimental results show that acid pickling reduces the surface impurities and therefore enhances the corrosion resistance of the alloy. The cleaning efficiency of the three acids used and the corrosion protection mechanisms were found to be remarkably different. Best corrosion results were obtained with nitric acid, followed closely by phosphoric acid. Only the sulphuric acid failed more or less when cleaning the AZ31 sheet. However, to obtain reasonable corrosion resistance at least 5 μm of the surface of AZ31 magnesium alloy sheet have to be removed.

Bee Wax Propolis Extract as Eco-Friendly Corrosion Inhibitors for 304SS in Sulfuric Acid

“…The effect of temperature towards the corrosion rate can be expressed by Arrhenius equation (3). The Arrhenius equation associated with an activation energy ( ) which is the minimum energy needed for the reaction to occur.…”

“…The process uses strong acids, such as hydrochloric acid (HCl) and sulfuric acid (H 2 SO 4 ) in various concentrations [3]. However, the high reactivity of sulfuric acid can cause the 304SS to be corroded.…”

Prediction of corrosion rate of AZ31B magnesium alloy under salt fog environment in NaCl solution

“…In the alloyed form, magnesium is the lightest structural metal and is a potential candidate to replace heavier aluminum or steel components, reducing fuel consumption and harmful emissions in the transport sector [2]. However, the use of magnesium alloys for structural applications has limited success due to their poor corrosion properties [3,4].…”

Acid Pickling/polishing of AZ31 Magnesium Alloy

“…On the other hand, chemical methods, especially, acid cleaning, could provide the best final polishing results [3]. Conventional magnesium etching liquids include inorganic acids such as hydrochloric acid, sulphuric acid, or nitric acid [4][5][6]. However, the magnesium etchant systems now in use have a variety of disadvantages and two of the major difficulties faced during etching of magnesium alloys are thick residual etching products and high surface roughness.…”