| Aluminum alloy is one type of important engineering material,but grain boundary corrosion and grain boundary precipitation associated performance degradation limit its applications.The recent progress in grain boundary engineering(GBE)reminds that,to optimize the grain boundary character distribution(GBCD)via GBE approaches is an effective way to solve such problems,and to study the grain boundary plane distribution(GBPD)and grain boundary inter-connection(GBIC)is the key point-cut for the GBE research and applications in aluminum alloys.In current research,Al-Cu binary alloys were used as experimental materials.The five-parameter analysis(FPA)based on electron back-scattered diffraction(EBSD)and stereological was used to study the influence of Cu content,annealing temperature,annealing time,pre-deformation and deformation mode on the recrystallization-relevant GBPDs and GBICs in the aluminum alloys.The main results are summarized as follows.The GBPDs and GBICs of the Al-Cu alloys,which had been processed by a multi-directional forging(MDF)followed by a annealing at 450 ? for 30 minutes,are obviously influenced by Cu content.It shows that though the GBPDs are mainly distributed on {1 1 1} regardless of Cu content,the intensity of this distribution in Al-2.3%Cu is evidently higher than that in Al-1.2%Cu.Although the GBICs of {1 1 1}/{1 1 1} including coherent twin boundaries are the most frequent ones out of the entire grain boundaries in the Al-Cu alloys with varied Cu content,the frequency of such GBICs in Al-2.3%Cu is obviously higher than that in Al-1.2%Cu.It also reveals that the two grains abutted by the grain boundaries with {1 1 1}/{1 1 1} GBICs usually share a common axis of<1 1 1>,<1 1 2>or<1 2 2>.After processed by MDF,Al-1.2%Cu alloy exhibits a regular changes in GBPDs and GBICs in the subsequent annealing at 300?,330? and 360? for 30 minutes,respectively.That is the GBPDs in the sample annealed at 300? are mainly distributed on {2 2 3}and {2 33},while that in the samples annealed at 330?and 360? are distributed on {1 1 1}.In the temperatures ranging from 300 ? to 360 ?,the frequency of {1 1 1}/{1 1 1} GBIC is increasing with annealing temperature going up.After processed by MDF,Al-1.2%Cu alloy also exhibits a regular changes in GBPDs and GBICs in the subsequent annealing at 360 ? for varied holding time.It shows that though the GBPDs are all distributed on {111} regardless of the holding time of annealing,the intensity of this distribution is remarkably increasing with the increment of holding time,and meanwhile,the frequency of {111}/{111} GBIC is increasing as well.For a Al-1.2%Cu alloy with an even microstructure and without preferred orientation,its GBPD and GBIC after recrystallization annealing at 390 ? for 2 minutes are affected by the pre-strain of cold rolling.When the pre-strain was 10%,the GBPD after recrystallization is mainly distributed on {2 2 3},and it evolves onto {1 1 1} with pre-strain increased to 20%.When the pre-strain reached 30%,the GBPD after recrystallization is still distributed on{111} with a scattering toward {2 2 3} and {2 3 3}.For the grain boundary of<1 1 1>/60°misorientation,which is the ?3 grain boundary,its relative frequency changed regularly with the increment of pre-strain,showing a clear increasing at first and then a slight decreasing with a peak value corresponding to the pre-strain of 20%.The frequency of {1 1 1}/{1 1 1}GBIC including coherent twin boundaries after recrystallization reaches its maximum when pre-strain was 20%.For a Al-1.2%Cu alloy with an even microstructure and without preferred orientation,its GBPD and GBIC after recrystallization annealing at 360 ? are also affected by the pre-strain mode of cold rolling.Compared to direct rolling,cross rolling is more efficient for the GBPD approaching to {1 1 1} and it is in favor of the formation of {1 1 1}/{1 1 1} GBIC in the subsequent recrystallization annealing.Based on the results above and the theory of crystallography,it is believed that the after-recrystallization GBPD mainly distributed on {1 1 1} is attributed to the lowest surface energy of this plane in Al-Cu alloys which exhibit a face-centered cubic(FCC)structure.{1 11}/{1 1 1} GBICs after recrystallization possess the most frequency indicate such GBICs are one type of low energy grain boundaries in Al-Cu alloys.So,in addition to the limited coherent twin boundaries,to pursue the grain boundaries with {1 1 1}/{1 1 1 } GBICs is an important orientation to the GBE research and applications for aluminum alloys... |
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