冷轧变形量和退火制度对超快速加热下5083铝合金晶粒尺寸的影响

利用Gleeble-3500热模拟系统和电子背散射衍射(EBSD)技术对5083铝合金的超快速退火组织演变规律进行研究,探讨了快速加热速度、退火温度及冷轧变形量对5083铝合金晶粒尺寸的影响。结果表明,5083铝合金经80%的冷轧变形后分别以25、250、500℃/s的加热速度升温至450℃保温3s后以40℃/s冷却时,平均晶粒尺寸随加热速度的增加由7.43μm细化至4.98μm。5083铝合金经80%冷轧变形后在不同退火温度(350、400、420、450和500℃)下进行超快速退火(加热速度500℃/s,保温时间3 s,冷却速度40℃/s)后,所得晶粒尺寸先减小再增大,在420℃退火时,晶粒尺寸达到最小,为4.82μm。再结晶晶粒尺寸受晶界迁移速率和形核率的耦合作用,在350~420℃超快速退火时,由于快速加热使形核率急剧增大,而形核温度较低,使晶界迁移速率较小,导致晶界迁移速率小于形核率,因而再结晶晶粒尺寸由5.23μm细化至4.82μm;在420~500℃超快速退火时,形核温度变高,晶界迁移速率快速增大,则晶界迁移速率大于形核率,使合金晶粒由4.82μm粗化至6.20μm,420℃是5083铝合金晶界迁移速率和形核率之间竞争的一个临界点。5083铝合金经50%、60%、71.4%、80%和87.5%的冷轧变形后以500℃/s的超快速加热速度升温至450℃保温3 s后以40℃/s冷却,所得平均晶粒尺寸分别为7.94、6.82、6.03、4.98和4.84μm,随轧制变形量的增大晶粒尺寸减小,但是冷轧制变量达到80%以后再进行超快速退火晶粒尺寸减小不明显。

Effect of cold rolling deformation and annealing process on grain size of 5083 aluminum alloy under ultra-fast heating

GLEEBLE-3500 thermal simulation system and EBSD technology were used to study the microstructure evolution of 5083 aluminum alloy under ultra-fast annealing.The effects of rapid heating rate,annealing temperature and cold rolling deformation on the grain size of 5083 aluminum alloy were discussed.The results show that the average grain size of 5083 aluminum alloy is refined from 7.43μm to 4.98μm with the increase of the heating rate from 25℃/s to 500℃/s.After ultra-fast annealing(heating rate 500℃/s,holding time 3 s,cooling rate 40℃/s)at different annealing temperatures(350,400,420,450 and 500℃),the grain size of the 80%cold-rolled 5083 aluminum alloy first decreases and then increases.When annealed at 420℃,the minimum grain size is 4.82μm.The grain size of recrystallization is affected by the interaction of boundary migration rate and nucleation rate.During the ultra-fast annealing at 350~420℃,the nucleation rate increases sharply due to the rapid heating,while the nucleation temperature is low,which makes the grain boundary migration rate smaller,resulting in the grain boundary migration rate less than the nucleation rate,and the recrystallization grain size is refined from 5.23 to 4.82μm;During the ultra-rapid annealing at 420~500℃,the nucleation temperature becomes higher and the grain boundary migration rate increases rapidly.The grain boundary migration rate is higher than the nucleation rate,which makes the grain coarsening from 4.82μm to 6.20μm.420℃is a critical point for the competition between the grain boundary migration rate and the nucleation rate of 5083 aluminum alloy.After 50%,60%,71.4%,80%and 87.5%cold rolling,5083 aluminum alloy is heated to 450 for℃3 s at an ultra-rapid heating rate of 500℃/s and cooled at 40℃/s;the average grain sizes are 7.94,6.82,6.03,4.98 and 4.84μm,respectively.With the increase of rolling deformation,the grain size decreases,but after the cold rolling reaches 80%,the grain size decreases unobviously.