机械球磨和热挤压制备超细晶5083铝合金的微观组织与力学性能研究

发布时间：2018-09-19 19:10

【摘要】：5083铝合金具有比较低的密度、较高的强度、较好的韧性、良好的耐蚀性等特点被广泛应用于飞机、汽车、船舶、发射塔、钻井平台、装甲车等领域。在轻量化、快速化、绿色化的要求下,现代航空航天和交通运输等领域对铝合金的性能提出了更高的要求。其中,细晶化即制备具有超细晶或者纳米晶组织的材料,是实现材料性能提升的一个发展方向。目前,粉末冶金方法是制备纳米晶/超细晶材料行之有效的方法之一。本文先通过室温机械球磨制备粉末,再利用热等静压处理和热挤压制备块体超细晶5083铝合金材料。通过采用透射电镜、扫描电镜、X射线衍射、金相分析等检测手段表征了粉末和块体材料的微观组织结构,同时研究了块体材料的力学性能、热稳定性、耐腐蚀性。研究了粉末和块体材料的微观组织结构。在惰性气体氛围保护下通过室温机械球磨来制备5083铝合金粉末。TEM观察表明其微观组织形貌是由等轴晶和拉长晶粒两种形貌组成,其中大约60%为等轴晶,40%为拉长晶粒,晶粒尺寸分布范围为20-150nm。热等静压处理后,拉长晶粒减小到10%左右。其中,400℃热等静压处理后(#24-1样品)平均晶粒尺寸为176nm,325℃热等静压处理后(#24-2样品)平均晶粒尺寸为157nm。热挤压后#24-1样品的平均晶粒尺寸达到371nm,#24-2样品的平均晶粒尺寸达到322nm。同时TEM观察到有第二相弥散分布在5083铝基体中。研究了Scherrer方法、积分宽度法、Voigt函数法计算A15083的晶粒大小。Scherrer方法由于没有考虑微观应变的影响,默认衍射峰产生的宽化全是由晶粒细化引起的,其计算出的晶粒尺寸普遍偏小。积分宽度法分为Cauchy-Cauchy、Gaussian-Gaussian、Cauchy-Gaussian三种方法。其中Cauchy-Cauchy方法假设晶粒细化和微观应变均接近柯西分布,计算结果偏大。Gaussian-Gaussian方法假设晶粒细化和微观应变均接近高斯分布,计算结果太小。Cauchy-Gaussian方法假设晶粒细化效应接近柯西分布,微观应变效应接近高斯分布,其计算结果更接近TEM统计结果,可以有效地计算晶粒大小。Voigt函数法中每条衍射线的计算结果都不同,取决于所选定的衍射线。研究了块体超细晶A15083样品的室温拉伸性能。实验结果表明#24-1样品的屈服强度为490 MPa,抗拉强度为497MPa,断后伸长率为8.7%。#24-2样品的屈服强度为560 MPa,抗拉强度为566 MPa,断后伸长率为6.3%,强度比传统5083铝合金材料有较大提高(60%左右)。断口分析显示其断裂方式属于微孔聚集型断裂。在理论分析的基础上半定量估算了各种强化机制对超细晶A15083材料强度的贡献,结果表明其强化机制包括细晶强化、弥散强化、固溶强化、位错强化,其中以细晶强化、弥散强化为主。研究了块体超细晶A15083样品的热稳定性。#24-1样品在400℃下进行退火,硬度为129±0.44HV,较退火前降低了 3.7%。屈服强度、抗拉强度分别是469 MPa、472MPa,较退火前分别降低了 4.3%和5.0%。#24-2样品在450℃下进行退火,硬度为138±0.61HV,较退火前降低了 3.5%。屈服强度、抗拉强度分别是505MPa、511MPa,较退火前分别降低了 9.8%和9.7%。#24-1样品和#24-2样品均表现出良好的热稳定性。研究了块体超细晶Al5083样品的耐腐蚀性。结果表现出较大的差异性,其主要影响因素包括金属表面的钝化膜、合金元素、晶粒细化。
[Abstract]:5083 aluminum alloy is widely used in aircraft, automobile, ship, launching tower, drilling platform, armored vehicle and other fields because of its low density, high strength, good toughness and good corrosion resistance. Among them, fine-grained is to prepare materials with ultra-fine or nano-crystalline structure, which is a development direction to improve the performance of materials. At present, powder metallurgy method is one of the effective methods to prepare nano-crystalline/ultra-fine-grained materials. Bulk ultrafine grain 5083 aluminum alloy was prepared by extrusion. The microstructure of powder and bulk materials was characterized by transmission electron microscopy, scanning electron microscopy, X-ray diffraction and metallographic analysis. The mechanical properties, thermal stability and corrosion resistance of bulk materials were studied. 5083 aluminum alloy powders were prepared by mechanical milling at room temperature under inert gas atmosphere. TEM observation showed that the microstructure of 5083 aluminum alloy powders was composed of equiaxed and elongated grains, of which about 60% were equiaxed grains, 40% were elongated grains, and the grain size distribution ranged from 20 nm to 150 nm. The average grain size of #24-1 sample after hot isostatic pressing at 400 (# 24-1 sample) is 176 nm, and that of # 24-2 sample after hot isostatic pressing at 325 (# 24-2 sample) is 157 nm. After hot extrusion, the average grain size of # 24-1 sample is 371 nm and that of # 24-2 sample is 322 nm. In aluminium matrix, Scherrer method, integral width method and Voigt function method are used to calculate the grain size of A15083. Because the effect of micro-strain is not taken into account, the broadening of default diffraction peak is caused by grain refinement, and the calculated grain size is generally small. The integral width method is divided into Cauchy-Cauchy, Gaussian-Gauss method. Cauchy-Cauchy method assumes that grain refinement and micro-strain are close to Cauchy distribution, and the results are larger. Gaussian-Gaussian method assumes that grain refinement and micro-strain are close to Gauss distribution, and the results are too small. The strain effect is close to the Gaussian distribution, and the calculated results are closer to the TEM statistical results, so the grain size can be calculated effectively. The calculated results of each diffraction line in Voigt function method are different, depending on the selected diffraction line. 90 MPa, 497 MPa tensile strength, 8.7% elongation after fracture. # 24-2 samples yield strength of 560 MPa, tensile strength of 566 MPa, elongation after fracture of 6.3%, strength than the traditional 5083 aluminum alloy material has been greatly improved (about 60%). Fracture analysis shows that the fracture mode belongs to microporous aggregate fracture. The results show that the strengthening mechanisms include fine grain strengthening, dispersion strengthening, solid solution strengthening and dislocation strengthening, among which fine grain strengthening and dispersion strengthening are the main ones. The yield strength and tensile strength were 469 MPa and 472 MPa respectively, which were 4.3% and 5.0% lower than those before annealing. The hardness of #24-2 sample was 138.61 HV and 3.5% lower than that before annealing. The yield strength and tensile strength were 505 MPa and 511 MPa, respectively, which were 9.8% and 9.7% lower than those before annealing. The corrosion resistance of bulk ultrafine grain Al5083 samples was studied. The results showed that the main factors affecting the corrosion resistance were passivation film on metal surface, alloy elements and grain refinement.
【学位授予单位】：山东大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG146.21;TG379

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