{111}/{111}Near Singular Boundaries in an Al-Zn-Mg-Cu Alloy Recrystallized After Rolling at Different Temperatures
Recent development in grain boundary design and control indicates that manipulating the{111}/{111}near singular boundaries will be a promising pertinent to improve the performance against in-tergranular corrosion attacks for the high stacking fault energy face-centered cubic metals such as alumi-num and its alloys.In the current study,five samples of a home-made Al-Zn-Mg-Cu super-high-strength aluminum alloy were rolled at temperatures of 250,300,350,400,and 450℃,followed by 30 min anneal-ing at 520℃.A method of grain boundary interconnection characterization based on electron backscatter diffraction and five parameter analysis was utilized to assess the{111}/{111}near singular boundaries in the samples as processed.The preceding rolling temperature was discovered to have a significant im-pact on the formation of{111}/{111}near singular boundaries during the subsequent annealing at 520℃,that is,the fraction of{111}/{111}near singular boundaries out of the entire grain boundaries increases at first and then decreases as the preceding rolling temperature increases from 250℃ to 450℃.In the five samples as processed,the one rolled at 300℃ followed by annealing at 520℃ has a peak content of{111}/{111}near singular boundaries and the fraction reaches 5.0%,which is 10 times higher compared to that of the singular boundaries or namely the coherent twin boundaries.Further investigations reveal that the sample rolled at 300℃ possesses a specific deformation substructure as well as suitable stored ener-gy,resulting in continuous recrystallization during the successive annealing.This type of behavior aids in the formation of{111}/{111}near singular boundaries.The samples rolled at or above 350℃,on the other hand,exhibit discontinuous dynamic recrystallization,which is detrimental to the development of{111}/{111}near singular boundaries during subsequent annealing.Compared to the sample rolled at 300℃,the sample rolled at 250℃ has higher stored energy and it improves discontinuous recrystallization dur-ing the subsequent annealing.This also harms the formation of{111}/{111}near singular boundaries.Off-line in-situ surface etching test and high-resolution transmission electron microscope(HR-TEM)observa-tion demonstrate that the{111}/{111}near singular boundaries have much higher resistance to intergranu-lar corrosion in comparison to the random boundaries,they possess disclination structures of which the atomic ordering is much higher than that of the random boundaries.The results show that the{111}/{111}near singular boundary is regulable,and to further improving the fraction of such boundaries by manipu-lating the microstructure evolution will be effective in the practice of how reducing the intergranular corro-sion in the aluminum and its alloys.
万方数据
维普
