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两阶段轧制变形过程中高强铝合金析出相与晶粒结构演变及其对性能的影响
发布人：上海艾荔艾合金股份有限公司www.shailiai.cn
更新时间：2016-06-24
与7055铝合金的传统热轧(CHR)对比, 制定了新的两阶段热轧工艺(DHR), 分别采用 CHR 和 DHR 对 7055 铝合金板材进行轧制, 研究了 DHR 工艺对7055铝合金析出相和亚结构的影响, 分析了 DHR 和 CHR 处理后合金组织、力学性能的差异.
两阶段轧制变形过程中高强铝合金析出相与晶粒结构演变及其对性能的影响PRECIPITATES AND THE EVOLUTION OF GRAIN
STRUCTURES DURING DOUBLE-STEP ROLLING OF
HIGH-STRENGTH ALUMINUM ALLOY AND RELATED
PROPERTIES
与 7055 铝合金的传统热轧(CHR)对比, 制定了新的两阶段热轧工艺(DHR), 分别采用 CHR 和 DHR 对
7055 铝合金板材进行轧制, 研究了 DHR 工艺对 7055 铝合金析出相和亚结构的影响, 分析了 DHR 和 CHR
处理后合金组织、力学性能的差异. 结果表明: 增加预变形量可提高析出相的球化程度(改变析出相形貌)
但不影响其面积分数; 中间高温短时退火可形成大量有序排布的亚结构; 后续进一步热轧过程中, 仍存在
的大量球形析出相钉扎位错和亚晶界, 且随累积应变增大, 小角晶界逐渐转变成大角晶界而使晶粒细化.
采用最佳的形变热处理工艺(固溶+预变形(300 ℃, 20%+中间退火(430 ℃, 5 min)+热变形(400 ℃, 60%))可在
保证高强度的同时使 7055 铝合金板材断后延伸率比 CHR 工艺提高约 25%.
The Al-Zn-Mg-Cu series alloys has been widely used in the aircraft, automotive, ship-building and
nuclear industries for the advantages of excellent combination of low density, high strength to weight ratio, good
toughness and high corrosion resistance, etc.. Most of the researchers focused on alloying and heat treatment at
aging temperature, however, rare work had paid attentions on the deformation process, and the microstructure
evolution and mechanical properties has not been analyzed completely. Grain refinement can not only improve the
strength and hardness, but also the plasticity and toughness of the alloy. Thermo mechanical treatment is an
efficient and economical treatment for obtain grain refinement by a combination the deformation and heat
treatment. In the present work, an improved thermo-mechanical processing, double step hot rolling (DHR),
including low temperature pre-deformation, intermediate short-term annealing and final hot rolling has been
proposed, aiming to investigate the microstructural evolution, deformation-induced precipitation and grain
refinement mechanism of the alloys during the DHR process. A 7055 aluminum plate has also been manufactured
by the conventional hot rolling (CHR) route. The corresponding microstructure evolution and mechanical
properties were investigated by OM, XRD, TEM, SEM, EBSD and tensile test. The results reveal that the grain
refinement is mainly preceded via dislocation rearrangement and low angle grain boundaries migration, which in
turn leads to the pinning effects of deformation induced precipitates. Low temperature pre-deformation can
accelerate the formation and spheroidization of fine precipitates. The pre-deformation makes influence on the
morphology and average size of precipitates without changing their area fraction. The precipitates generated by
the pre-deformation can exert significant drag force to the migration of the grain boundaries and dislocation
movements, which subsequently promotes the formation of dislocation cells. Although some smaller particles
have been dissolved into the matrix during intermediate annealing treatment, some particles are still fine and can
pin the dislocation boundaries. At the same time, the activated dislocation boundaries rearranged to form polygon
sub-grains. Grains are further elongated after the final hot rolling. The low angle grain boundaries (like sub-grain
boundaries) into high angle grain boundaries transition will be accelerated if the motion of boundaries is impeded
by the particles. And the new small grains formed near the original grain boundaries can finally cause the
fine-grained structures. The results indicate that the optimum thermo-mechanical treatment of 7055 aluminum
alloy may be solid heat treatment + pre-deformation (300 ℃, 20%) + intermediate annealing (430 ℃, 5 min) + hot deformation (400 ℃, 60%). The elongation of the alloy produced by the proposed process can increase by 25%
without strength loss comparing with that of conventional hot rolling. And the present DHR process is supposed to
be a good alternative manufacturing process for the Al alloys to obtain fine grain structured heat-treatable sheets.
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