Corrosion Behavior Of Al-Mg-Mn-Sc-Zr Alloy Plate And Welded Joints

The novel microalloyed Al-Mg-Mn-Sc-Zr alloys have excellent properties,such as high specific strength,excellent formability and weldability,and have been used in the aerospace field.At present,there is insufficient research on the corrosion behavior of Al-Mg-Mn-Sc-Zr alloys and their welded joints.In this paper,aiming at the lack of data support for the application of the alloy in corrosive environment,Al-Mg-Mn-Sc-Zr alloy sheets were subjected to the stabilization annealing treatment,welding（VPPAW and TIGW）and micro-arc oxidation treatment.Using exfoliation corrosion,intergranular corrosion,stress corrosion,and electrochemical corrosion combined with microstructure,the corrosion behavior of Al-Mg-Mn-Sc-Zr alloy plates,welded joints,and MAO coatings in corrosive solutions was systematically studied.The mechanism of corrosion resistance of Al-Mg-Mn-Sc-Zr alloy was discussed.The exfoliation corrosion and intergranular corrosion behaviors of Al-Mg-Mn-Sc-Zr alloy in etching solution were studied.The results showed that the EXCO and IGC properties of Al-Mg-Mn-Sc-Zr alloy are closely related to the distribution,morphology and precipitation of theβ（Al₃Mg₂）phase.The precipitation of the continuousβphase at the grain boundaries can significantly reduce the EXCO and IGC resistance of the alloy.In particular,when annealing is performed at 225°C,a large number of continuous,coarseβprecipitate phases are formed at the grain boundaries,and the corrosion resistance is the weakest.When the stabilization annealing temperature reaches above 300℃,the continuous network structure of theβphase is destroyed due to the rapid recovery of the dislocation structure with high energy,thereby significantly reducing the corrosion susceptibility of the Al-Mg-Mn-Sc-Zr alloy sheet.The microstructure and corrosion behavior of Al-Mg-Mn-Sc-Zr alloy VPPA welded joints were investigated.The results show that the bond zone（BZ）has the poorest corrosion resistance.The size,shape and distribution of Al（Mn,Fe）intermetallic particles in different regions are different mainly due to VPPA welding.The higher density of the iron-rich phase in the BZ causes a great cathodic reaction,resulting in poor corrosion resistance in the BZ.The BM region has good corrosion resistance.Aiming at the Al-Mg-Mn-Sc-Zr alloy TIG welded joint,the crack propagation behavior of Al-Mg-Mn-Sc-Zr alloy in 3.5%Na Cl corrosion solution was studied by the direct current voltage drop method（DCPD）.The stress corrosion crack growth rate of TIG-welded Al-Mg-Mn-Sc-Zr alloy base material（BM）and weld zone（WZ）in 3.5%Na Cl solution was tested by 1/2 CT specimen,and the crack growth behavior was studied.The results show that the critical stress intensity factor K_ⅠSCCof stress corrosion cracking of the BM is 7.05 MPa·m^1/2,and the K_ⅠSCCof the WZ is 11.79 MPa·m^1/2.The growth rate of stress corrosion cracking in the BM is faster than that in the WZ,and the WZ is less sensitive to stress corrosion cracking.The stress corrosion cracking in the BM area is in the transgranular mode,while the stress corrosion cracking in the WZ area is in the transgranular and intergranular fracture modes.The corrosion resistance of Al-Mg-Mn-Sc-Zr alloy MAO coatings prepared with different concentrations of Na₂Si O₃electrolytes was systematically studied by the electrochemical corrosion method.The results show that the MAO coating is mainly composed ofγ-Al₂O₃andα-Al₂O₃phases.When the concentration of Na₂Si O₃solution in the electrolyte is 7 g/L,the MAO coating with the best corrosion resistance can be obtained,which can be attributed to the fewer surface cracks and pores of the MAO coating.