《泡沫铝材料的制备与有限元模拟》由会员分享，可在线阅读，更多相关《泡沫铝材料的制备与有限元模拟（118页珍藏版）》请在金锄头文库上搜索。
1、 I 摘摘 要要 泡沫铝材料是一种在铝或铝合金基体中均匀分布着大量孔洞的新型轻质多功能材料，它包括泡沫纯铝和各种泡沫铝合金材料。本论文在泡沫铝材料制备方面主要研究了粉末冶金与熔体发泡法两种工艺。 在粉末冶金法制备工艺中，首先研究了压制和烧结工艺对压坯发泡性的影响，然后研究了发泡温度、发泡时间、发泡剂含量对泡沫铝孔隙率和结构的影响，得到的最佳工艺为：铝粉与为 2 wt%发泡剂混合均匀后，在 350 MPa 的压力下初压成型，随后在 400 烧结 40 min，再在 150 MPa 压力下压制得到发泡预制品，最后，在 720 发泡 12 min，得到孔结构较均匀，孔隙率 80%的泡沫铝。 在熔体发
2、泡法制备工艺中，研究了搅拌时间、发泡温度、发泡剂含量、铝粉的加入量对孔结构和孔隙率的影响。结果表明：选用铝硅合金（AlSi7Mg0.45)为基体材料，采用粒径 74 150m 的铝粉增粘，在固定其它工艺为最佳条件下，仅通过改变铝粉含量实现了孔径大小控制。 得出的最佳工艺为： 铝粉含量 515 wt%， 增粘搅拌时间 7 min，发泡温度 650 0C，发泡剂 1.5wt%，得到孔结构均匀，孔隙率为 8085%，孔径为2.08.5mm 的泡沫铝硅合金。 通过对泡沫铝材料的发泡过程中气泡形核和长大动力学过程的分析， 铝熔体中气泡的形核过程为非均相形核，得出了气泡形核的活性孔隙尺寸范围，同时推导出气
3、泡生长过程中半径 r 与时间 t 的关系，及球形气孔理论上的最大半径。 依据熔体发泡法制备的不同孔径泡沫铝硅材料的实验结果， 分析表明铝粉增粘后的铝合金熔体为非牛顿流体，其粘度可用 Vand 式进行表示，同时对理论推导所得的半径公式进行修正，使其成为适合铝粉增粘发泡法制备泡沫铝硅合金的孔径公式。 泡沫铝硅合金的力学性能结果表明， 泡沫铝硅合金的单向压缩形变经历三个区域, 在各区内的应力-应变特征符合 Ashby 模型，即线性弹性区、平台区和致密化区。 根据应力-应变曲线，计算了泡沫铝硅合金的吸能能力及吸能效率，结果表明：其吸能能力，取决于应力和应变，与密度之间呈非单调关系，在某一密度时，具有最
4、大值。泡沫铝硅合金的吸能效率随应变的增加，达到最大值后开始下降。泡沫铝硅合II 金密度越低，平台区越长，在平台区变形范围内，能量吸收效率达 80%以上。 建立了三种泡沫铝模型：模型 1（不均匀结构） 、模型 2（均匀结构） 、和模型 3（大孔缺陷结构） 。与常用的周期性六边形蜂窝模型相比，所建立的模型更符合实际泡沫铝材料的结构。利用 ANSYS 软件对建立的模型进行有限元分析，得出其弹性模量和密度呈指数关系。 根据泡沫铝硅合金的测试结果和弹性模量模拟结果， 利用有限元 ANSYS /LS-DYNA 软件分别对空心圆管保险杠和不同密度泡沫铝硅合金填充的圆管保险杠进行了有限元模拟。结果表明：与传统
5、的空心圆管保险杠相比，泡沫铝填充的圆管保险杠，不仅重量减轻了，而且所采用管的个数和相对体积也减少。其中，采用密度为 0.56 g/cm3泡沫铝填充的圆管，重量减轻了 34%，体积减少了 57%，所需个数减少 21 根。 关键词：泡沫铝 粉末冶金 熔体发泡法 发泡动力学 能量吸收 有限元 弹性模量 保险杠 III Abstract Foamed pure aluminium and various foamed aluminium alloys are a kind of novel light-weighted functional materials characteried by mass
6、 holes dispersed in the parent material. In this thesis two techniques, powder metallurgy and melt foaming for fabricating foamed aluminium and aluminium alloys, were mainly studied. Regarding the fabrication of foamed aluminum by powder metallurgy, the influence of pressing and sintering processes
7、on the foaming of aluminium were investigated; the dynamics during the sintering process was also analyzed. By investigating the effects of foaming process parameters on the porosity and structure, we have obtained the optimized process as follows: Firstly press the powder under a pressure of 350MPa
8、, then sinter for 40 minutes in the air atmosphere at 400 and press again at 150MPa, at last, foam for 12 minutes at 720. The best foaming-agent dosage is 2wt%. This leads to the fabrication of foamed aluminium that has a well-proportioned structure with a porosity of 80%. In the melt foaming proces
9、s, on the other hand, aluminium powder within the granule size of 74150m was used for melt thickening through the increases in viscidity of the melt aluminium and stabilization of the gas that was formed from the decomposition of the foaming-agent. The influence of mixing time, foaming temperature,
10、foaming-agent dosage and the amount of aluminium powder on the porosity and the pore structure was investigated. According to these results, the pore size can be changed under control only by changing the dosage of aluminium powder while other parameters were kept the optimized values. The optimized
11、 processing conditions are: Aluminium powder dosage of 515%wt%, blended for 7 min at 650, foaming agent dosage of 1.5wt%. Using this technics, foamed AlSi7Mg0.45 alloy with well structure, porosity within 8085% and pore size within 2.08.5mm was fabricated. The dynamics of nucleation and growth of th
12、e pores during the foaming process was conducted. The effectual pore sizes range in the melt aluminium in case of heterogeneous and homogeneous nucleation were deduced respectively, also the relation between the radius r of the pore and foaming time t was carried out, by which the maximum size of sp
13、here pore was calculated. According to the experiment results of the different pore sizes obtained in the melt foaming process, the viscidity of the aluminium melt after adding aluminium powders was IV found to be close to that of mine slurry and belonged to the non-Newtonian fluid. The viscidity of
14、 which can be expressed by formula “Vand”. The theoretic formula of the pore size was amended to the expressions appropriate for the melt foaming process in which aluminium was added to increase the viscidity. Mechanical property testing revealed that the compressive stress-strain of the foamed AlSi
15、7Mg0.45 went through three phases including linear elastic zone, platform zone and the densifing zone. The relation between stress and strain in every stage can be well described by the Ashby model. Based on the stress-strain curves, the energy absorption capability was calcultaed. It was found that
16、, under the same strain, the energy absorption capability decreases with the decreases of density. However with increasing strain, the energy absorption efficiency of foamed metal increases initially and then decreases. The lower the density, the longer the plateau line is. The energy absorption efficiency is over 80% within the platform zone. Three models for different foamed aluminium were established, i.e., model I for unhomogenous structure, model II for
