【作者】 曲家惠；

【导师】 王福；

【作者基本信息】 东北大学 ， 材料学， 2008， 博士

【摘要】 镁合金在塑性变形时由于强烈的变形织构存在,变形后容易产生各向异性,影响进一步的加工。通过工艺控制与优化,调控材料的织构类型和数量,是提高或改善镁合金加工性能的重要途径,更是它能否得到更广泛应用的一个关键因素。所以成为材料科学工作者不断探索与研究的领域之一。本文以AZ31镁合金为研究对象,对其实施不同条件的塑性变形和热处理,通过金相观察、SEM和TEM观察以及X射线衍射等手段,对其在不同的塑性变形和热处理条件下,该合金的显微组织和晶体取向流变行为进行了系统研究。这些结果不仅对具有六方系结构材料的形变与再结晶的研究具有理论意义,而且也为工业生产提供技术原型。首先进行热挤压变形,在162℃挤压变形得到混晶组织,有Mg17Al12和MnAl相析出。随着挤压温度的升高,析出相减少。在258℃时没有MnAl相析出,Mg17Al12相也很少。但是,挤压变形时容易发生动态再结晶,随着形变量增大,平均晶粒尺寸减小,组织越均匀,当挤压比为λ=25时能得到平均晶粒尺寸为7.3μm的均匀组织,为改善其塑性变形能力提供有利的组织条件。320℃挤压变形时,组织较均匀,析出物更少。织构分析表明：AZ31镁合金变形初期形成典型的{0001}纤维织构,随着形变量增大,动态再结晶过程产生{0221}、{1231}再结晶织构,漫散程度也变大。变形和动态再结晶的共同作用使变形织构和再结晶织构均不能得到充分发展。当挤压比为λ=25时,变形织构{0110}和再结晶织构{0221}、{1231}面的强度相近且很弱,有利于降低改善各向异性,提高或改善加工和成型性能。电场退火和常规退火不同。电场退火推迟了AZ31镁合金再结晶进程,抑制晶粒长大,并使织构漫散。在热挤压变形的基础上,又进行了自由锻的组织和织构分析。组织不均匀,锻造中产生的{1217}、{1214}、{0115}等面织构,其强度随着形变量的变化而变化。强的面织构增加材料的各向异性,不利于改善镁合金的塑性变形能力和力学性能。在模锻时,模具的设计要考虑材料的各向异性的影响。取厚度为1.4mm的热轧板,分别进行同步单向冷轧、交叉冷轧和不同速比的异步冷轧研究。在同步单向冷轧时,{0001}面织构组分强度趋向均匀分布,且随形变量ε的增加,{0001}<1010>和{0001}<2110>织构组分的强度呈波动性增加,当形变量ε≥15%时,出现切变带后而断裂。在交叉冷轧时,{0001}面织构组分随形变量ε的增加向{0001}<2110>聚集,且{0001}<1010>开始稍有增强后呈现减弱,相反{0001}<2110>却连续增加,当形变量ε≥5.8%时,出现切变带后而断裂,对该合金,交叉冷轧是无益的。采用室温下异步冷轧时,速比和形变量对织构转变均有影响：随速比的增加,与快、慢辊侧相接触的表面层明显不同,但中间区域变化不明显。在快速辊侧,主要织构组份{0117}<514192>和{0001}<1210>随速比的增加而迅速增加；在慢速辊侧,主要织构组份{0117}<514192>和{0001}<1210>随速比的增加而交替变化。随形变量的增加,主要织构组份{0117}<514192>和{0001}<1210>的强度增加,只是快速辊侧显著的大于慢速辊侧。选择合适工艺,采用异步轧制,可以在室温条件下,以单道次高达20%的形变量轧成表面平整光滑的镁合金薄板。室温下异步冷轧镁合金板是可行的。更多还原

【Abstract】 The strong anisotropy of deformation Magnesium alloy which comes from the plastic deformation textures affects the further materials process. The techniques controlling and optimization to improve the texture component and intensity are important approach of Magnesium alloy forming properties, and a key factor to expand the application in more fields. So the texture controlling of deformation Magnesium alloy has become one of the continuously research fields.In this paper, the as-received AZ31 Mg alloy was possessed and annealed in different conditions. Microstructures and textures in the present samples were performed by optical microscopy (OM), scan electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffraction, respectively, the microstructure and crystal orientation of material flow behavior are studied in detail. All the results have remarkable theoretical significance of the study in deformation and recrystallization hexagonal lattice materials, and also providing the technical antitype for industry production.By the hot extrusion deformation at 162℃, the mixed metallurgical structure with precipitation of Mg17Al12 and MnAl are obtained. The precipitation decreases with the increase of hot extrusion temperature. When hot extrusion at 258℃, there are no MnAl precipitation and fewer Mg17Al12 precipitation. The dynamic recrystallization is easy occurring during hot extrusion, the average grains size decrease and microstructure homogeneous with the increase of true strain. The average grains size is 7.3μm with homogeneous microstructure at the extrusion ratioλ=25, which provides advantaged condition for improving plastic forming ability of Magnesium alloy. The microstructure becomes more homogeneous and fewer precipitation at 320℃hot extrusion. The texture results show: at deformation early stage of AZ31 Magnesium alloy, the typical {0001} fiber texture can be obtained, the dynamic recrystallization texture components of {0221}、{1231} occur and the dispersion degree increase. Deformation and dynamic recrystallization texture can not be developed fully by the collective effect of deformation and recrystallization. The intensity of deformation texture component {0110} is similar to the recrystallization texture components {0221},{1231} with weak intensity, this situation is benefit to decrease the anisotropy, therefore to improve the forming properties. The annealing at electric field and normal is different. Rerystallization process of AZ31 Magnesium alloy is delayed, the grain growth blocked and grain orientation is dispersed at electric field annealing.Based on the hot extrusion forming, the microstructure and texture are studied on the flat die forging. The heterogeneous microstructure and {1217}、{1214}、{0115} texture components change with the increase of forming rate. Strong texture enhances the anisotropy of materials, which make against the plastic deformation ability.and mechanics properties of Magnesium alloy. The design of die should be considered the effect of anisotropy during forging.Directional rolling, cross rolling and cross shear rolling (CSR) with different mismatch speed ratios (MSR) are performed on 1.4mm thickness hot rolling sheet. The intensity of {0001} texture component presents homogeneous distribution and increase with the increase of strainεduring directional cold rolling. The intensities of {0001}<1010> and {0001}<2110> texture components increase by wave way, shear bands occur and then breakage when strainε≥15%.{0001} texture component gathers to {0001}<2110> texture component with the strain increase during cross rolling, and {0001}<1010> texture component has a light increase at the beginning then this texture component decrease, otherwise {0001}<2110> increase continuously, shear bands occur and then breakage when strainε≥5.8%. Cross rolling have no merit for this kind of alloy.Textures are affected by the speed ratio and deformation degree at room temperature cold cross shear rolling:the center zone has no remarkable change, the surface near to the fast mill roll side is obvious different to that near to the slow mill roll side. On the fast mill roll side, the main texture component of {0117}<514192> and {0001}<1210> increase rapidly with the increase of speed ratio; on the slow mill roll side, the main texture components {0117}<514192>和{0001}<1210> alternate increase with the increase of speed ratio. The main texture components {0117}<514192> and {0001}<1210> increase with the increase of strain, but fast mill roll side is more remarkable than that of slow roll side. With appropriate techniques by cold cross shear rolling, the smooth surface of Magnesium alloy sheet can be obtained by using of 20% deformation degree each gate under room temperature. It is feasible to produce the Magnesium alloy sheet by cold cross shear rolling.更多还原