The Relationship Between Corrosion Behavior And Microstructure In AA2024 Aluminum Alloy

Because of the good mechanical properties,AA2024 alloy is one of the most commonly used alloy in Al-Cu-Mg aluminum alloy.However,due to the high corrosion sensitivity,the service life is reduced,so it is very necessary to study the cause of corrosion of the alloy.In this paper,by micro-Vickers hardness test,room temperature tensile test,constant load stress corrosion test,static corrosion test and intergranular corrosion test,and with a lot of analysis methods,such like scanning electron microscopy?SEM?,energy spectrum?EDS?,electron back scattering diffraction?EBSD?and transmission electron microscope?TEM?,the relationship between corrosion behavior and microstructure in AA2024 aluminum alloy has been systematically investigated from the following aspects:The first is about the influence of precipitation microstructure change on the stress corrosion behavior of AA2024 aluminum alloy;the second is about the relationship between the second phase particles and the corrosion behavior of AA2024 aluminum alloy;The last is about the influence of deformation and aging on the microstructures and mechanical properties of 2024 aluminum alloy.And the main results are as follows:?1?The stress corrosion susceptibility of the AA2024-T3 sample is different from that of the T8 sample.The stress corrosion resistance of the T8 alloy with grain corrosion is better than that of the T3 alloy with intergranular corrosion.The corrosion process was investigated by in-situ corrosion observations operated by high-angle annular dark-field scanning TEM?HAADF-STEM?,which intuitively demonstrate the different corrosion morphologies.Due to the precipitation of the Mg-rich S phase in the grain boundaries of the alloy after T8 treatment,so the morphology of the alloy with intergranular corrosion and grain corrosion is combined.And because stress promotes the more directional intergranular corrosion than the promotion of grain erosion,the T8 state alloy has better stress corrosion resistance.?2?There are a large number of second phase particles in AA2024-T3 alloy,which mainly include Al₂CuMg particles,AlCuFeMn particles and AlCuFeMnSi particles.In this paper,the quasi-in-situ trace experiments by scanning electron microscopy showed that the concentration of NaCl etching solution does not affect the initial corrosion rate of Al₂CuMg particles,and the Mg in the particles preferentially corrodes during the corrosion process.This is due to the low Mg potential,so it is prone to corrosion.The corrosion resistance of AlCuFeMn particles is better than that of Al₂CuMg particles,but the corrosion may also occur.It is mostly the pore-like corrosion pits and the morphologies of pits and corrosion trenches coexisting.The corrosion resistance of AlCuFeMnSi particles is best among the three kinds of particles,and the particles with Cu/Fe ratio of about 1.0 are hardly corroded in NaCl solution.This may be due to the fact that the content of Cu and Fe is not much different and the composition is relatively uniform,and it?s potential is higher than the aluminum substrate as a cathode,so the particles are difficult to corrode.?3?After 50%cold-rolling of AA2024-T3 alloy,the grain size was significantly refined,the grain boundary was disorderly rearranged,and the propo rtion of high-angle grain boundaries decreased.When a large number of dislocations are introduced,the hardness and tensile strength of the alloy are greatly increased,but the elongation rate is reduced.Due to the change of the grain boundary microstructure,the resistance to intergranular corrosion of the alloy is improved.The deformed sample was artificially aged at 180°C,part of the dislocations reverted,but the precipitation strengthening effect gradually increased,and just 3 h to peak aging at179 HV.As the aging time extended,the hardness decreases because of precipitation coarsening.After testing the corrosion performance of the alloy,it was found that the depth of intergranular corrosion of the deformation aging sample was greater than that of the deformed sample only.This is because the precipitation of S phase at the grain boundary promotes the occurrence of corrosion.And,due to the change in corrosion behavior,its stress corrosion resistance is improved.