Formation Mechanism And Regulation Of {111}/{111} Near Singular Boundaries In Ultra-High Strength Aluminum Alloys

The application of ultra-high strength aluminum alloy which has excellent comprehensive properties in many field is limited due to its lack of resistance to grain boundary corrosion.Taking grain boundary itself as the research object,the effect of different compression strain rates and compression temperature on{111}/{111}near singular grain boundaries in ultra-high strength aluminum alloys have been studied with the quantitation characterization method based on electron backscatter diffraction technology and five-parameter analysis.This paper provides an important practical basis for exploring the formation mechanism of{111}/{11 1}near singular grain boundaries in the process of microstructure reconstruction,and further regulating such grain boundaries to improve the grain boundary corrosion resistance of ultra-high strength aluminum alloys.The results of this paper are summarized as follows:The formation of{111}/{111}near singular grain boundary is significantly affected by different strain rates on the continuous static recrystallization of ultra-high strength aluminum alloy.After two-stage solution and repeated multi-direction hot forging,the ultra-high strength aluminum alloy was compressed at 300℃with strain rate of 0.001s^-1,0.01s^-1and 0.1s^-1and deformation of 70%,and then the recrystallization annealing was completed at 520℃/30min.The proportion of{111}/{111}near singular grain boundaries increases with the increase of compressive strain rate.The proportion of{111}/{111}near the singular grain boundary is5.23%at maximum in the compressed samples with strain rate of 0.1s^-1.The experimental results show that continuous static recrystallization occurs during the deformation and microstructure reconstruction of samples compressed at 300℃at a strain rate of 0.1s^-1,which promotes the formation of{111}/{111}near singular grain boundaries.Compression at different temperature has a significant effect on the formation of continuous dynamic recrystallization{111}/{111}near singular grain boundary in ultra-high strength aluminum alloy.After two-stage solution and cold rolling annealing,the ultra-high strength aluminum alloy was compressed at 450℃,480℃and 520℃with strain rate of 0.001s^-1and deformation of 70%.The experimental results show that there are more low angle grain boundaries in the samples with high temperature and low strain rate,and the proportion of{1 11}/{111}near singular grain boundaries in low angle grain boundaries is higher than that in high angle grain boundaries.The content of{111}/{111}near singular grain boundaries increases with the increase of compression temperature.There is the highest proportion of near singular boundary in the sample compressed at 520℃.The content of{111}/{111}-NSB in low angle grain boundary is 8.77%,and that in high angle is 4.53%.The results show that continuous dynamic recrystallization is conducive to the formation of{111}/{111}near singular grain boundaries.The formation of{111}/{111}near singular grain boundary is significantly affected by different strain rates on the continuous dynamic recrystallization of ultra-high strength aluminum alloy.The ultra-high strength aluminum alloy was compressed at 520℃with strain rates of 0.1s^-1,0.01s^-1and 0.001s^-1and deformation of 70%after two-stage solution and cold rolling annealing.The experimental results show that the proportion of{111}/{111}near singular grain boundaries decreases with the increase of compressive strain rate.The proportion of{111}/{1 11}-NSB is the highest in the samples compressed at the strain rate of0.001s^-1,and which is the lowest in the samples compressed at the strain rate of 0.1s^-1.Comprehension analysis of the above experimental results show that there will be higher proportion of{111}/{111}-NSB in ultra-high strength aluminum alloy at high temperature and slow strain rate.The results of off-line in-situ corrosion experiments shows that the corrosion resistance of{111}/{111}near singular grain boundaries in ultra-high strength aluminum alloy is markedly stronger than that of general high angle boundaries.The formation of{111}/{111}near singular grain boundaries is closely related to continuous dynamic recrystallization.There will be a higher proportion of{111}/{111}-NSB by further precisely regulating the continuous dynamic recrystallization behavior,which is expected to significantly improve the grain corrosion performance of Al-Zn-Mg-Cu ultra-high strength aluminum alloy.