| Magnesium alloys are widely used as structural materials which could greatly reduce the weigth of vehicles. However, corrosion is the key point that hinders its application. In this paper, traditional electrochemical methods in combination with weight loss, hydrogen evolution and surface analysis methods are used to investigate the corrosion behaviors of Mg alloy Mg-10Gd-3Y-0.5Zr (GW103) and galvanic corrosion of Mg alloy coupled to Al alloy, Cu and carbon steel as well as the inhibition effects of inhibitors on corrosion and galvanic corrosion of Mg alloy in ethylene glycol solution at ambient and elevated temperatures. Mechanisms of Mg and its alloys AZ31and AZ91D in sodium chloride solution are studied, respectively. The main research work and results are as follows:1. The corrosion performance of magnesium-based rare-earth containing alloy GW103was evaluated in an ethylene glycol solution with a group of selected aliphatic, aromatic carboxylates and inorganic salts as inhibitors. Based on these results, an inorganic-organic sodim phosphate-sodium dodecylbenzenesulfonate (SDBS) inhibitor package was designed. It was found that the corrosion rate of GW103decreased by adding1000ppm of the inorganic-organic inhibitors at both ambient and elevated temperatures. The inhibitors were more effective at the ambient temperature than at the elevated temperature. The corrosion of GW103in the ethylene glycol solution can be effectively inhibited by1000ppm of the inorganic-organic inhibitors. It is believed that the added phosphate can interact with SDBS, resulting in a more compact surface film on the GW103surface. A synergistic mechanism was proposed to explain the inhibition behavior of the sodium phosphate-SDBS combination, and the effect on the surface film on GW103was investigated.2. The galvanic corrosion of GW103and AZ91D coupled to an Al alloy (A7005) in an ethylene glycol (EG) solution at ambient (25℃) and elevated temperatures (90℃) was investigated by means of open circuit potential (OCP), coupling potential (CP), galvanic current density, potentiodynamic polarization curve and electrochemical impedance spectroscopy (EIS). Moreover, weight loss measurement and ESEM were also employed to investigate the galvanic corrosion damage of the coupled Mg alloys. The galvanic corrosion behaviors of the couples were compared in the ethylene glycol solution before and after adding the sodium phosphate-SDBS inhibitors. It was found that both the general corrosion and galvanic corrosion of the Mg alloys were mitigated by the organic-inorganic inhibitor package. The most interesting finding was that the anode and cathode of the Mg alloy-Al alloy couples were reversed by addition of the inorganic and organic inhibitors into the blank EG solution. The anode-cathode reversal can be attributed to the OCP changes of the anode and cathode after inhibitor addition. The measured galvanic behavior was in good agreement with the theory predictions.The galvanic corrosion behaviors of the couples were compared in the EG solution before and after adding sodium phosphate with SDBS and sodium phosphate with benzoate, respectively. It was found that the general corrosion of the Mg alloys was mitigated by the organic-inorganic inhibitor package. Phosphate with SDBS has better inhibition efficiency on the self corrosion of Mg alloys at both ambient and high temperatures. However, phosphate with benzoate has a better inhibition effect on the galvanic corrosion of Mg alloys coupled to carbon steel and Cu.3. The inhibitive effects of the investigated inhibitors on the corrosion behaviors of Mg and its alloys of AZ31and AZ91D inl wt.%NaCl were studied. The results show that AZ91D has the largest corrosion resistance and AZ31shows the highest corrosion rate in the NaCl solution, and the inhibition efficiencies of the inhibitors on Mg and its alloys were different which may be due to the difference in alloy microstructure, content and distribution of the P phase, and the inhibition mechanisms.
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