Investigation On Corrosion Behavior Of 7055Al And Al-0.2Zr Alloys

As a kind of super-high strength Al-alloy,7055 Al has a high strength,low density and large specific strength.It has been extensively applied in aviation,spaceflight,energy and electric power and other industries.It has high content of Zn,Mg in order to improve the mechanical properties.However pitting corrosion,intergranular corrosion and other corrosion often occur,resulting in decrease corrosion resistance.Al-Zr/Al-Zr-B series of aluminum alloys are a kind of heat-resistant aluminum alloy and can reach to 180 MPa.However adding Zr can reduce the heat-strength loss.It is necessary to investigate its corrosion behavior because the effect of Zr addition on corrosion resistance is still not clearIn this paper the microstrutcture corrosion behavior of 7055 Al and Al-0.2Zr were investigated by exfoliation test,intergranular corrosion,electrochemical test ansd SEM/EDS,experimental results are follows.The corrosion resistance of 7055 Al was studied by electrochemical method.It was found that the alloys in regression re-aging(RRA)state possess the best corrosion resistance,the samples in artificial aging state(T6)are the poorest and extruded alloy has moderate corrosion resistance.The weak acid environment can contribute to the appearance of hydrogen evolution corrosion.The corrosion morphology shows pitting and intergranular in neutral solution,while uniform corrosion acid in solution;p H value has no obvious influence on Epit.Through the exfoliation test,EDS,SEM,metallographic observation and other methods,the corrosion behavior of 7055 Al was studied and it is found that 7055Al-T6 in the initial stage of the formation of oxide film formed on 7055Al-T6,was destroyed by the Cl-.And then it was quickly dissolved;the extruded alloy remained the resistance to corrosion with several hours;the oxide film was damaged after 20 h immersion.The corrosion morphology was observed by scanning electron microscope,and 7055Al-T6 was found that there appeared flack of Al3 Fe and Al Fe Si Mn phases in the center.?? and Mg Si2 anode phase dissolved,there existed only shallow holes at the edges of the specimen,no obvious exfoliation morphology was found;Both T6 and the extruded alloys had intergranular corrosion.Corrosion sensitivity of these three types(extruded,T6,RRA)of 7055 Al was investigated.It is found that the corrosion morphology of the extruded 7055 Al is pitting corrosion,the corrosion morphology of T6 microstructure is pitting and intergranular corrosion,for the 7055Al-RRA,there was no intergranular corrosion only pits existing,The corrosion resistance and corrosion morphology of Al-0.2Zr alloy was studied by electrochemical test and metallographic observation,The results showed that the the corrosion resistance of Al-0.2Zr aged at 220? was ranked from high to low aging 2h> 10h>14h>8h.The corrosion morphology exhibited slight pitting for the 2h aged alloys,while the 8h aged alloy showed severe pitting.