Effects Of Zr/Sc+Zr On Hot Deformation And Corrosion Behavior Of Al-Mg Alloy And Its SSFSW Joint

Al-Mg alloys have the advantages of light weight,medium strength,and corrosion resistance,and are widely used in ships and aerospace fields.Microalloying is a commonly used method for strengthening and toughening of aluminum alloys,but its influence on thermal deformation and post-weld corrosion performance of alloys remains to be further revealed.Combined with the Natural Science Foundation of Hunan Province,this paper takes Al-Mg,Al-Mg-Zr and Al-Mg-Sc-Zr alloys as research objects,and uses thermal simulation experiments,corrosion tests and microscopic characterization methods to study the effect mechanism of Zr/Sc+Zr on the hot compression of Al-Mg alloy and the corrosion behavior of static shoulder friction stir welded（SSFSW）joints.The research results will further enrich the microalloying theory and expand the application scope of Al-Mg alloy and SSFSW technology.The main conclusions are as follows:（1）The homogenized Al-Mg,Al-Mg-Zr and Al-Mg-Sc-Zr alloy ingots were subjected to hot compression deformation under the conditions of300℃-500℃and 0.001s^-1-1s^-1.The true stress-true strain curve of friction correction is used to construct the rheological constitutive equation.The constitutive equations of the three alloys are as follows:（?）（2）The thermal processing map was constructed based on the DMM model.The results show that the addition of Zr/Sc+Zr reduces the range of the instability zone of the Al-Mg alloy at low temperature,but expands the range of the instability zone at high temperature and high strain rate.And the addition of Zr/Sc+Zr can increase the dislocation density in the hot deformed grains of Al-Mg alloy,inhibit the occurrence of recrystallization and increase the strain energy.At 500℃-1 s^-1,Al-Mg-Sc-Zr alloy exhibited hot compression cracking due to the accumulation of dislocations in the grains and the increase of strain energy.（3）The most sensitive areas for corrosion of Al-Mg and Al-Mg-Sc-Zr alloy SSFSW joints are located in TMAZ-AS.The maximum intergranular corrosion depth,hydrogen evolution corrosion rate,electrochemical corrosion density and dislocation density in the former area are:263±2μm,1.47±0.08 ml?cm^-2/h,5.85±0.07μA?cm^-2 and 4.08±0.03×10¹⁶m^-2,the latter corresponding values are:200±3μm,0.25±0.04 ml?cm^-2/h,3.89±0.02μA?cm^-2 and 1.97±0.05×10¹⁷ m^-2.In addition,Sc+Zr can reduce the stress corrosion susceptibility factor of Al-Mg alloy SSFSW joint from0.581±0.02 to 0.479±0.02.The reason why TMAZ-AS is the most sensitive to stress corrosion is that in the Al-Mg and Al-Mg-Sc-Zr welded joints,the dislocation density on the TMAZ-AS is the largest,and it has the largest coupling current density and the most negative current density with the weld nugget zone.（4）The highest stability occurs in WNZ and TMAZ-AS due to the largest dislocation density on the advancing side of the thermomechanical affected zone in the Al-Mg and Al-Mg-Sc-Zr welded joints and the largest difference in the microstructure of the weld nugget and heat affected zone galvanic current density and maximum negative coupling potential,galvanic coupling is the strongest,and the risk of galvanic corrosion is greatest.resulting in stress corrosion cracking in TMAZ-AS.（5）Sc+Zr improves the corrosion performance of Al-Mg alloy SSFSW joints,which can be attributed to the fact that Al₃（Sc,Zr）nanoparticles can strongly pin dislocations and grain boundaries,reduce the joint grain size and the percentage of high-angle grain boundaries,inhibit the segregation of Mg,Fe and Si elements at grain boundaries.