Effect of Mn content on microstructure and corrosion resistance of the Zn-Al-Mg alloys
In order to improve the corrosion resistance of hot-dip galvanized products,three types of Zn-Al-Mg alloy ingots with different Mn contents were prepared by induction melting.The compositions were Zn1Al1Mg0.5Mn,Zn1Al1Mg1.2Mn、and Zn1Al1Mg2.5Mn,respectively.And their solidified microstructure and corrosion behavior were analyzed.The results show that the predicted types of Al-Mn compounds are Al11Mn4,Al8Mn5 and Al0.8Mn through phase diagram calculations.The Al-Mn pre-cipitates in Zn1Al1Mg0.5Mn and Zn1Al1Mg1.2Mn alloys are Al11Mn,and Al8Mn5,respectively.As the Mn content increases,the Al-Mn precipitates in Zn1Al1Mg2.5Mn alloy are Al8Mn5 and Al0.8Mn.Al11Mn4 and Al8Mn5 mainly precipitate at grain boundaries,while Al0.8Mn mainly precipitates inside the pure zinc phase.As the Mn content increases,the self corrosion current density decreases and the impedance value increases,Zn1 Al1Mg2.5Mn alloy has the best corrosion resistance.Due to the dispers-ed distribution of Al0.8Mn with a hexagonal crystal structure in the pure zinc phase,the precipitation strengthening effect genera-ted refines the solidification structure of the alloy,and can generate a dense oxide film during the corrosion process,slowing down the corrosion rate of the alloy coating and improving the corrosion resistance of the Zn1Al1Mg2.5Mn alloy.
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