Evaluation Of Temperature Resistance Of Magnesium Alloy Sacrificial Anode And Study On Resistances To High Temperature Of Aluminum Alloy Sacrificial Anode

Magnesium alloy sacrificial anode shows good electrochemical performances including negative potential,high output current and high driving potential for steel at room temperature.Aluminum alloy possesses large theoretical capacitance,high current efficiency,moderate driving potential for steel and rich resources.Thus magnesium and aluminum alloy sacrificial anode have been widely applied in metal protection in various environmental media.However,electrochemical performance of aluminum anode sharply deteriorates with temperature increasing,unable to meet the requirements of protecting steel structures at high temperature.Also,electrochemical performances of magnesium anode with temperature variation need to be further explored.Consequently,the effect of temperature on the performances of magnesium alloy anode and high temperature resistant aluminum alloy sacrificial anode have been studied in this paper,providing support for application of magnesium and aluminium alloy anodes at high temperature.The main results are as follows:1.Study on electrochemical performances of MIC,AZ31,AZ63 magnesium alloy anode at different temperatureAccording to GB/T 17848-1999,the electrochemical performances of the anodes have been evaluated in artificial seawater and fresh water at 25⁷0?and their depth of etching pit were mearsured.The effects of temperature on polarization behavior of the anodes before and after accelerated testing have been studied by polarization curve measurement.The results show that with temperature increasing,the local corrosion of three anodes obviously accelerates but the actual capacitance and current efficiency increase slightly.The actual capacitance and current efficiency of three anodes in two different media have little difference,manifesting indistinctive effects of temperature and medium on the magnesium alloy anodes.2.Study on the effects of mixed rare earth?RE?on electrochemical behavior of aluminum alloy at high temperatureTo improve the inhomogeneous corrosion and enhance low current efficiency of Al-Zn-In-Mg-Si alloy anode?F anode?at high temperature,Al-Zn-In-Mg-Si-xRE?x=0.09,0.17,0.34 and 0.62wt.%?alloys?FR anode?have been developed.The effects of RE addition on microstructures and electrochemical performances of the alloys have been studied with conventional experiments,potentiodynamic polarization,EIS,SEM and XRD.The results show that FR containing 0.17 wt%RE?FR-0.17%RE?possesses the most excellent microstructures and electrochemical performances.The main precipitation phases are Al₂LaZn₂ and Al₂CeZn₂ particles.The favourable electrochemical performances of FR-0.17%RE are mainly attributive to the fine grains and grain boundaries containing fine precipitates.Fine grains would improve the inhomogeneous corrosion of FR-0.17%RE at the same time,resulting in current efficiency of 82.075%in formation water at 70?and atmospheric pressure.3.Study on electrochemical behavior of aluminum alloy in simulated deep well environmentThe corrosion behavior and performances of F and FR-0.17%RE in simulated deep well environment also have been studied.The results exhibit that the corrosion rate of F and FR-0.17%RE is accelerated under 6 MPa and 70?due to the acceleration of cathode process.The efficiency of F and FR-0.17%RE sharply decreases under high temperature and pressure,related to the increase of useless loss in weight(?_loss)and the decrease of discharge capacity.Taking FR-0.17%RE as an example,the calculated design parameters of the corresponding steel cathodic protection signify that an increase of 24%of the anode consumption is at least required in deep well environment.