Effect of voltage on gas composition of 15%SiCp/2009 aluminum matrix composite during microarc discharge process
The microarc oxidation(MAO)tests for the 15%SiCp/2009 aluminum matrix composite under different voltages were carried out in a silicate solution.The anode gas released from microarc discharge process of 15%SiCp/2009 aluminum matrix composite was collected,and its composition was analyzed.Then,the influence of voltage on the anode gas composition was evaluated,the generation mechanism of anode gas was also discussed.The results show that the anode gas at different voltages consists of H2,O2 and trace CO,which is different from that oxygen releases from the anode as suggested by the traditional electrochemical theory.In the range of 360-440 V,with the increase of voltage,the intensity of discharge spark increases,the growth rate of MAO coating also accelerates,moreover,the H2 content increases,and the O2 content decreases correspondingly.When the voltage exceeds 440 V,the anode gas composition keeps stable,the H2 content(volume fraction)is about 80%,and the O2 content is only about 20%.A large amount of H2 and O2 are released from the thermal decomposition of water in the spark discharge region,and the more intense the discharge,the more the water decomposes.The oxidation reaction between aluminum and water,and the high energy electron-impact dissociation of water molecules in the discharge region are also the important sources for the generation of excess H2.In addition,the SiC reinforcement participates in the coating forming process,and is oxidized to release the trace CO at the spark discharge region with the high temperature.
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