【作者】 孙亚飞；

【导师】 王群骄；

【作者基本信息】 东北大学 ， 材料加工工程， 2008， 硕士

【摘要】 镁合金是迄今在工程中应用的最轻的结构材料。同时,镁合金具有比强度和比刚度高、减振性能好、电磁屏蔽效果佳等优点,因此在汽车工业、通讯电子、航空航天工业等领域正得到日益广泛的应用。镁资源非常丰富,在许多传统金属矿产资源趋于枯竭的今天,开发镁合金的应用对保持资源的可持续性发展具有战略意义。大多数镁合金具有密排六方结构,压力加工成形性能差,而大多数镁合金又具有良好的铸造性能,使得目前镁合金产品以铸件居多。然而,铸件的力学性能不够理想,导致镁合金的使用受到很大的限制。因此,变形镁合金的研究已成为世界镁工业发展中的重要方向。为了提高AZ31镁合金的综合力学性能,尤其是塑性,本文以实验为基础,选择AZ31镁合金为研究对象,将Φ153mm均匀化处理后的锭坯分别在250℃、300℃和350℃进行挤压,然后分别在330℃和370℃进行轧制和在250℃和400℃进行热处理,通过金相观察、拉伸性能测试、拉伸断口扫描、X射线衍射织构分析,研究了挤压温度、轧制温度和热处理温度对板材力学性能的影响,本文还探讨了冷轧与热轧对镁合金板材力学性能的不同影响,获得了以下结论：1.挤压温度对AZ31镁合金板坯的表面质量及力学性能具有重要影响。当在300℃挤压时,可以得到表面质量优良的板坯,且获得的板材力学性能优良,因此,合适的挤压温度为300℃；2.轧制温度对AZ31镁合金板材的力学性能也有很大影响。当在370℃轧制时,最大道次压下量可达49.14%,所获得的板材晶粒均匀细小,平均晶粒大小为3-4μm,且获得的板材力学性能优良,因此,合适的轧制温度为370℃；3.合适的轧后热处理制度为250℃×20min,热处理后变形过程中所形成的孪晶消失,基本完成再结晶,AZ31镁合金板材的强度有所下降而塑性大幅度提高。抗拉强度由轧制态的305MPa降为热处理后的280MPa(横向),而延伸率由轧制态的18.24%上升到热处理后的21.37%(横向)；4.通过适当的冷轧工艺及热处理工艺可以大幅度提高AZ31镁合金板材的力学性能。当将2mm厚的AZ31镁合金粗轧板坯冷轧制到0.9mm厚时,AZ31镁合金板材表现出了优良的力学性能,经过250℃×20min热处理后,抗拉强度可达到横向的265MPa和轧向的260MPa,延伸率可达到横向的30.08%和轧向的27.36%；5.AZ31镁合金在不同轧制方式下(冷轧和热轧)形成了不同的织构类型,在冷轧板材中,织构强度较弱,主要有(0117)[0772](90°,15°,0°)、和(1129)[1239](75°,20°，30°)织构；在热轧板材中,织构为以基面织构为主的较强板织构。冷轧板材的织构中形成双峰特征,反映出合金的不同变形机制。冷轧具有改变织构主要组分、弱化织构强度的作用,理论上表明冷轧可以提高镁合金板材的成形性能；经过热处理后,AZ31镁合金板材的主要织构组分不变,但强度下降；6.晶粒尺寸、孪晶和织构是影响AZ31镁合金板材强度、塑性和各向异性的重要因素,通过控制轧制、热处理等工艺,可以改变晶粒尺寸、孪晶和织构,达到在保证强度的前提下,提高塑性、降低各向异性的目的。更多还原

【Abstract】 Magnesium alloy is until now the lightest structural material in the project application. At the same time, magnesium alloy is being increasingly wider using in the automobile industry, the communication electron, aviation and aerospace industry and other fields because of its merit, such as high specific strength, good electromagnetic shielding and good damping property. There is abundant storage resource of magnesium on the earth, and at the present time, many of the traditional metal mineral resources become depleting, the development of the application of magnesium alloy to maintain the sustaining development is strategic significance. Most of magnesium alloy has the hexagonal close-packed structure, and formability is not very well, and most of magnesium alloy has the good casting property, so most of magnesium alloy components are mostly produced by die-casting at the present time. However, mechanical properties of the casting products are not very ideal, which restricts the application of AZ31 magnesium alloy. Therefore, research on deforming magnesium alloy become very important in the magnesium industrial fields.In order to enhance the comprehensive mechanical properties of AZ31 magnesium alloy, particularly plasticity, in the present study, based on experiments, AZ31 magnesium alloy was chosen as object of material, AZ31 billets with diameters ofΦ153mm, after homogenization treatment, were extruded at 250℃,300℃and 350℃, respectively. AZ31 extruded plates were rough-rolled at 330℃and 370℃, respectively. Finally, AZ31 thin sheets were obtained after finishing rolling, AZ31 thin sheets were annealed at 250℃and 400℃, respectively. In order to study the contribution of extruding temperature, rolling temperature and heat treatment temperature on mechanical properties of AZ31 magnesium alloy sheets, microstructures were examined, tensile property were tested, fractures were scanned and X-ray texture measurement were also performed. Effect of cold-rolling and hot-rolling on AZ31 magnesium alloy sheet was also explored in this article, and the main conclusions are followings:1. Extruding temperature has a great influence on surface qualities and mechanical properties of AZ31 magnesium alloy sheet. AZ31 magnesium alloy extruded plate with good surface and mechanical properties can be obtained when ingots was extruded at 300℃. Therefore appropriate extruding temperature is 300℃.2. Rolling temperature has also a great influence on mechanical properties of AZ31 magnesium alloy sheet. When AZ31 extruded plates were rolled at 370℃, the maximal reduction reached 49.14%, homogeneous and fine grains were obtained, whose average size is 3-4μm with good mechanical properties. Therefore appropriate rolling temperature is 370℃.3. Proper heat treatment system is 250℃×20min, crystal grains of hot-rolled AZ31 magnesium alloy sheet became regular, twin which formed in deforming disappeared, and recrystallization nearly finished, after annealling at 250℃. Tensile strength of AZ31 magnesium alloy sheet was decreased, at the same time, elongation percentage increased largely. The tensile strength of AZ31 magnesium alloy sheet decreased from 305MPa to 280MPa (transverse direction). Meanwhile, the elongation percentage increased from 18.24% to 21.37%(transverse direction).4. After annealling at 250℃, the cold-rolled AZ31 magnesium alloy sheet with thickness of 0.9mm has good mechanical properties, whose transverse tensile strength get to 265MPa, while transverse elongation percentage get to 30.08%, and longitudinal tensile strength get to 260MPa, while longitudinal elongation percentage get to 27.36%.5. AZ31 magnesium alloy has formed the different texture types under the different rolling ways (cold rolling and hot rolling). In cold-rolled sheet, texture type are mainly (0117) [0772] (90°,15°,0°) and (1129) [1239] (75°,20°,30°). In hot-rolled sheet, texture is basal fiber. In pole figures, two peaks appears in AZ31 cold-rolled sheet, meanwhile one peak appears in AZ31 hot-rolled sheet, which shows different foming mechanisms in cold rolling and hot rolling. Cold rolling changes the texture type and weakens the intensity, which shows cold rollinghas the property of enhancing formobility of AZ31 sheet. Heat treatment can not change texture type, but weaken intensity of texture.6. Grain size, twin and texture are three key factors which affect strength, elongation and aeolotropy of AZ31 magnesium alloy sheet. By controlling the parameters of rolling, heat treatment and other technologies, grain size, twin and texture can be changed, the perpose of increasing plasticity and decreasing aeolotropy can be achieved without the decrease of strength.更多还原