【作者】 丁茹；

【导师】 王伯健；

【作者基本信息】 西安建筑科技大学 ， 材料加工工程， 2010， 硕士

【摘要】 本文采用厚度为3mm的商用热挤压AZ31镁合金板坯在上辊直径为：135mm、下辊直径为：120mm的异径两辊轧机上进行轧制,研究了不同轧制工艺、热处理工艺及其对板材组织和性能的影响,探讨了板材的断裂行为。实验结果表明：(1)在本实验条件下：异速比1.125,轧制温度300℃,AZ31镁合金板材单道次大变形异步轧制存在一个临界压下率εC,当压下率≤εC时,板材的组织和力学性能随变形量的增加而改善；当压下率>εC时,板材的组织和力学性能将从所达到的最佳状态下降。(2)道次压下率为38.1%的单道次和两道次大变形异步轧制工艺所得板材均具有细小的等轴再结晶组织,其晶粒尺寸分别从原始的13.6μm减小到2.8μm和1.0μm,板材的抗拉强度从275MPa分别增加到328MPa和350MPa,伸长率从22.2%分别增加到26.5%和30.8%,板材内部织构均得到了一定程度的软化；轧制后板材在经过300℃×30min退火后,组织均匀化程度显著提高,晶粒尺寸略有增大,分别为3.3μm和2.1μm,抗拉强度分别下降了3.96%和4.0%,伸长率分别提高了24.5%和21.1%。(3)异步轧制后热轧态AZ31镁合金板材的组织和性能在随后的加热过程中的变化与退火工艺具有密切的关系。在200℃退火时,随保温时间的延长,板材的组织和力学性能均未发生太大的变化；在300℃退火30min,板材组织发生了再结晶过程,获得均匀细小的等轴晶,当保温时间增加到60min时,存在部分再结晶晶粒长大；在350℃退火30min和60min,均在完成再结晶的同时晶粒长大；在300℃和350℃不同保温时间退火后,板材的抗拉强度和伸长率均发生了显著变化；在300℃×30min退火后,压下率为38.1%的单道次异步轧制AZ31镁合金板材的综合性能较好,室温抗拉强度为315MPa,伸长率为33.0%；(4)压下率为38.1%和44.5%的AZ31镁合金板材经不同的退火处理后,二者的平均晶粒尺寸、显微硬度、抗拉强度和伸长率变化规律相似；所不同的是,与压下率为38.1%的异步轧制板材相比,压下率为44.5%的在350℃退火60min时,存在晶粒异常长大现象；(5)通过SEM分析得到：经两道次异步轧制后,AZ31镁合金板材的断裂单元明显减小,韧性断裂特征越来越显著。更多还原

【Abstract】 The commercial hot-extruded AZ31 plates measuring 3mm in thickness were used in the study. The DSR process was performed on a mill of different upper and lower roller diameters, which was 135mm and 120mm, respectively. Different DSR processes, heat treatment processes and their influences on the microstructure and properties of AZ31 magnesium alloy sheets were investigated in this paper. Fracture behavior of sheets was also involved.The results showed that:(1) Under the experimental conditions, a critical deformationεC existed in one-pass large deformation DSR with the rolling speed ratio of 1.125 and temperature of 300℃. Microstructure and properties of sheets improved with increasing deformation and declined from the reached best condition when the deformation was≤εC and＞εC respectively.(2) Both of the one-pass and two-pass large deformation DSR processes with pass reduction of 38.1% gained fine equiaxed recrystallized grains. The grain sizes were refined from 13.6μm to 2.8μm and 1.0μm respectively, tensile strength increased from 275MPa to 328MPa and 350MPa respectively, elongation increased from 22.2% to 26.5% and 30.8% respectively, and textures of both were softened to some extent. After annealing at 300℃for 30min, the grains of the two DSR sheets were significantly homogenized. Grain sizes were 3.3μm and 2.1μm respectively, tensile strength decreasing rates were 3.96% and 4.0% respectively, and elongation increasing rates were 24.5% and 21.1% respectively. So it was possible to enhance ductility significantly while keeping the strength slightly reduced by differential speed rolling with subsequent annealing treatment.(3) Microstructure and properties of hot-rolled AZ31 magnesium alloy sheets had a close relationship with the annealing temperature and holding time. The results indicated that microstructure and properties were not undergone any significant changes when annealing at 200℃with increasing the holding time, because of the only occurance of static recovery in these annealing processes.30 minutes of annealing at 300℃were enough to fully recrystallize the microstructure and gain fine and homogeneous equiaxed grains. Part recrystallized grains grew up when the holding time increased to 60min at 300℃. Grains grew up after full recrystallization when annealing at 350℃for 30min and 60min.Significant changes had occurred in tensile strength and elongation when annealing at 300℃and 350℃with different holding time. An optimized mechanical property with tensile strength of 315MPa and elongation of 33.0% was achieved in sheets of 38.1% deformation after annealing at 300℃for 30 min.(4) The variation of average grain size, microhardness, tensile strength and elongation of AZ31 Mg alloy sheets with deformation of 38.1% and 44.5% was similar under different annealing process. When annealing at 350℃for 60min, there was somewhat different. A small number of abnormal grains occurred in sheets of deformation of 44.5% leading to the significant reduction in properties under this annealing process, while there were all normal grains in sheets of deformation of 38.1% under the same annealing process.(5) The SEM analysis showed that after the two-pass DSR process, fracture units reduced visiblely and the ductile rupture feature becomed more and more significant.更多还原