Investigation On Intergranular Corrosion Of2024Aluminum Alloy

2024aluminum alloy is an alloy that can be strengthened by heat treatment. It hasgood plasticity, fracture toughness, extensibility and fatigue crack resistance and is widelyused in the aerospace field, but its corrosion resistance is worse. In this paper,2024aluminum alloy is chosen as the research object and with the potentiodynamic polarizationcurve, electrochemical impedance spectroscopy, intergranular corrosion experiments, saltspray test and total immersion test, the intergranular corrosion resistance is investigated.Moreover, the microstructural components and corrosion morphology are analyzed byoptical microscope, scanning electron microscopy and energy dispersive spectrometer.The experiment is firstly to ascertain heat process for2024aluminum alloy and theprecipitated phase after heating processing is characterized by energy dispersivespectrometer. Using the intergranular corrosion experiments, the corrosion morphology ofthe three surfaces such as the rolling and the two section surfaces and the corrosion depthof each surface of2024aluminum alloy are observed to study the effect of grainorientation and size on the intergranular corrosion. In the tests of salt spray and totalimmersion, the corrosion resistance of2024aluminum alloy in the corrosive medium ofNaCl solution under different heating processing is further studied.The main part of the experiment is to test the potentiodynamic polarization curve andelectrochemical impedance spectroscopy of2024aluminum alloy by using theelectrochemical workstation. To have a better understand of the corrosion resistance, thepolarization curve and impedance spectroscopy of the three cross section of2024aluminum alloy are tested in aerated and deaerated3.5wt%NaCl solution. Through thetest diagram and the fitted electrochemical values, the comparison and analysis in kineticsare performed. The ageing precipitated phase of2024aluminum alloy is analyzed by EDS and theresults are shown that the coarse phase precipitated in the intracrystalline is mainlyAlCuFeMnSi.The effect of heat process of2024aluminum alloy on the intergranular corrosion isstudied and it shows that under the same corrosion medium, the air-cooled samples aremost susceptible to be corroded. Moreover, intergranular corrosion appeared in larger areaof the sample. The maximum corrosion depth of the aging samples ranked from deep toshallow are overaged, underaged and peakaged, respectively, and the corrosion model ispitting corrosion and local intergranular corrosion.2024aluminum alloy with different heat process is corroded using total immersiontest and the corrosion rate ranked from small to large are water-quenched, air-cooled,underaged, peakaged and overaged, respectively. The corrosion model is intergranularcorrosion and pitting corrosion.2024aluminum alloy with different heat process is also investigated using salt spraytest, and intergranular corrosion was more serious with the peakaged and as-rolledsamples.At last, the corrosion behavior of2024aluminum alloy with different heat process ismeasured by using electrochemical technology. Obvious passivating regions appeared indeaerated NaCl solution. Whether in aerated or deaerated solution, the water-quenchedsamples have the best corrosion resistance. Moreover, the corrosion resistance of the L-STsurface in the three surfaces of the sample is best.