| Nickel aluminum bronze is widely used in aerospace,marine engineering,heat exchanger,medical equipment and other fields because of its good corrosion resistance and good mechanical properties.The general commercial nickel-aluminium bronze alloy contains 9~12 wt.% aluminium,but its structure and other properties are obviously different when it is in this range.Most of the former research mainly focus in p H,nickel content,surface treatment,heat treatment,adding rare earth elements on the influence of nickel aluminum bronze corrosion resistance,the effects of aluminum content of nickel aluminum bronze rarely reported.The research object of this paper is nickel aluminum bronze with different aluminum content,the influence of aluminum content on aluminum bronze structure and corrosion resistance was studied by means of electrochemical testing and physical property.The NAB alloy with 5,7,9,11 and 13 wt.% aluminum is prepared by the medium frequency furnace.The metallographic microstructure of NAB alloy was observed,the microstructure of NAB alloy was observed by scanning electron microscope,the chemical components of different tissues were analyzed by energy spectrometer,and the phase structure of the substance was analyzed by XRD.5 ~ 9 wt.% aluminum content of nickel aluminum bronze has the similar microstructure,give priority to with α,11 ~ 13 wt.% aluminum content of nickel aluminum bronze is β phase as the matrix,XRD phase analysis of 11 ~ 13 wt.% aluminum NAB alloy,there is a small amount of ternary compound τ phase in the meet Al7Cu23 Ni and Al7Cu4 Ni characteristic diffraction peak.The corrosion resistance of NAB alloy with different aluminum content in 3.5wt.% neutral salt solution was studied by measuring C350 electrochemical workstation.In neutral salt water for a sample after polishing,the open circuit potential stability after the immersion time were measured for 20 minutes of open circuit potential,potentiodynamic scanning and immersion time for 30 days,potentiodynamic scanning at the same time measure samples without the polarization of the soaking time is 6 ~ 30 days(every 6 days)of the electrochemical impedance spectroscopy.The tafel constant and corrosion rate were obtained by fitting the dynamic potential scanning curve with the tafel traditional method,and the corrosion resistance of the alloy was compared.Zsimpwin matching corresponding equivalent circuit was used to analyze and fit the electrochemical impedance data,and the corrosion process and corrosion resistance of the surface were determined according to the obtained resistance value.The results showed that the corrosion products were not formed and the corrosion characteristics were not obvious in the beginning of immersion time.With the increase of soaking time,the formation and stability of corrosion products showed significant difference,and the corrosion rate values were different greatly.In this paper,scanning electron microscope and energy spectrometer were used to observe the morphology of samples after corrosion and analyze the composition of corrosion products.The corrosion mechanism of NAB alloy was discussed.The corrosion resistance of the samples increased as the soaking time extended,is due to the alloy surface of Cu2 O and Al2O3 protection to metal substrate,the main corrosion products as a protective base alloy type copper chloride Cu2(OH)3 Cl,shows a pair of diamond particles.Analysis of alloy microstructure and electrochemical testing results for NAB alloy corrosion mechanism is as follows: in 3.5% Na Cl solution,α corrosion resistance is best,α + κ eutectoid predominate part first began to erode,corrosion resistance is less than α,β phase increasing of aluminium content increases eutectoid and produce γ2,the corrosion resistance of γ2 is relatively low.Therefore,there are dense Cu2 O and Al2O3 protective layers on the surface of nickel aluminum bronze with 9 wt.% aluminum content,and the α phase is taken as the matrix,and the γ2 is not analyzed,showing the best corrosion resistance. |
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