时效预处理态Al-Zn-Mg-Cu合金热变形及其后热处理过程中晶粒组织的演变

Grain Evolution during Hot Deformation and Subsequent Heat Treatments Processes of As-aging Pre-treated Al-Zn-Mg-Cu Alloy

以435℃/2 h＋200℃/12 h固溶时效预处理的新型Al-Zn-Mg-Cu高强铝合金为研究对象,在温度350-400℃,应变速率0.01-1 s-1和变形量60%-80%条件下进行热压缩变形,再经350℃/0.5 h＋470℃/2 h退火和固溶处理。采用光学（OM）、电子显微镜（EBSD、TEM）组织观察和测试方法,研究了时效预处理析出相粒子对热压缩变形及随后退火和固溶处理过程中晶粒组织的演变机理和规律。结果表明：（1）在400℃、0-05 s-1、60%条件下,ln Z值为24.33,发生了连续动态再结晶,获得了细小均匀的再结晶晶粒组织;经退火和固溶处理后,晶粒趋于等轴状,尺寸稍有增加,最终获得细小均匀的晶粒组织。（2）在380℃、0.1 s-1、60%条件下,ln Z值增加到25左右,晶粒沿变形方向拉长,晶界断续分布着细小的再结晶晶粒;经退火和固溶处理后,晶粒长大不明显,在变形拉长的晶粒内部均匀分布着尺寸较小的回复亚晶粒。（3）当应变速率较快或变形温度较低,ln Z值增加到约26,且变形量较大时,动态再结晶不明显,晶粒沿变形方向剧烈拉长;经退火和固溶处理处理后,晶粒长大明显,最终获得粗大的晶粒组织。

A new AI-Zn-Mg-Cu high strength aluminum alloy after solution and aging pre-treatments of 435 ℃/2 h＋200 ℃/12 h was taken as the object and hot compressions at temperatures in the range of 350-400 ℃, strain rates in the range of 0.01 to 1 s1 and height reduction up to 60%-80% were carried out followed by subsequent annealing and solution treatments of 350 ℃/0.5 h＋470 ℃/2 h. The influences of precipitated particles on grain evolution mechanisms and regulations during hot deformation and subsequent annealing and solution treatments were investigated by optical microscope （OM） and electronic microscope （EBSD, TEM）. The conclusions can be drawn as following. （i） Continuous dynamic recrystallization occurs under deformation conditions of 400 ℃, 0-05 s-1, 60%, the value of lnZ is 24.33, and refined and uniform recrystallized grains appear. After subsequent annealing and solution treatments, recrystallized grains become more equiaxed and uniform, and the size of grains increases slightly. As a result, the refined, equiaxed and uniformly-distributed grain structure occurs. （ii） When hot compression is carried out under conditions of 380 ℃, 0.1 s-1, 60%, the value of lnZ increases to 25 or so, grains are elongated along the deformation direction with some refined recrystallized grains at the grain-boundaries. After subsequent annealing and solution treatments, grain growth is not too much, and refined and recovered well sub-grains come forth evenly in the elongated grains. As a result, the elongated grain structure with refined and uniform sub-grains emerges. （iii） At other conditions of increased strain rates or decreased temperatures, the value of lnZ increases to about 26, and deformation increases to large values, dynamic recrystallization can not be observed obviously and the prior grains are elongated severely. After subsequent annealing and solution treatments, the grains grow rapidly. As a result, the coarse grain structure appears.