【作者】 李大武；

【导师】 孙挺；

【作者基本信息】 东北大学 ， 材料物理与化学， 2010， 博士

【摘要】 泡沫铝是一种由金属骨架和泡孔组成的新型多功能材料,具有质轻、吸声、隔声、电磁屏蔽、吸能缓冲、隔热、耐火等优良特性,可广泛应用于交通运输、建筑机械、冶金化工、电子通讯和航天航空等多个领域,其研究成为当今世界材料科学高技术领域的重要研究、开发内容之一。熔体发泡法是泡沫铝生产的主要方式之一,该法是在熔融的金属中,利用发泡剂分解产生的气体滞留在熔体内部而使金属发泡,经冷却后得到泡沫固体(闭孔泡沫)。在泡沫铝的生产中,发泡剂的选择尤为关键,不同的发泡剂具有不同的分解特性,在熔体中因分解产生气体而具有不同的发泡效果。本文采用氢化稀土和氢化锆作为发泡剂熔体直接发泡法制备纯铝基泡沫铝材料的实验研究。对于发泡剂氢化稀土,程序升温热重法研究了热分解行为。实验表明当温度超过760℃,氢化稀土开始呈现出大幅度失重现象。XRD结果表明氢化稀土易吸水形成氢氧化物,需要密封保存。对发泡剂ZrH2,利用程序升温热重法研究了其热分解行为,并与TiHH2进行了对比；详细考察了升温速率对DTA谱图的影响。分析了分解过程中的动力学与热力学特征,以及发泡气体与熔体之间可能的反应；研究了ZrH2在熔体中的分布对泡沫铝的影响。结果表明ZrH2于500℃出现较小的吸热峰,750℃时出现尖锐吸热峰。当升温速率较低时,ZrH2的氧化符合化学反应控制模式,当升温速率较高时,ZrH2的氧化符合固体产物层扩散控制模式。Zr和Ca元素在泡沫铝中分布具有明显差别,而气泡集体上浮则是引起泡沫铝中元素分布差异的主要原因。采用氢化稀土和氢化锆,熔体发泡法制备泡沫铝,讨论了工艺条件对泡沫铝孔径的影响。考察了发泡温度,发泡剂含量,增黏剂Ca的加入量,搅拌时间和保温时间对泡沫铝制品的影响；并对泡沫铝产品进行了孔径分析和力学性能测试。结果表明ZrH2制备的泡沫铝孔径均匀,平均孔径在1-2mm,适合制备小孔经的泡沫铝产品；氢化稀土制备的泡沫铝孔径较大,并不均匀。氢化稀土和氢化锆混合发泡具有较好的发泡效果,孔径较为均匀。优化了泡沫铝的最佳制备条件；对氢化稀土,氢化稀土发泡剂加入量为2％～2.5％(mass),发泡温度为750±10℃,搅拌时间1.00min～1.25min,保温时间2.50min；用氢化稀土+氢化钛混合发泡剂制备泡沫铝,叮以得到孔径及分布很均匀的样品,具体的工艺参数为：发泡剂加入量为2%(mass),发泡剂配比氢化稀土/氢化钛为8.5/1.5～8.0/2.0,发泡温度730±10℃,搅拌时间1.00min,保温时间3min；采用ZrH2作为发泡剂,在坩埚内制备泡沫铝材料的工艺条件和参数为：ZrH2发泡剂加入量为0.8%～1.0%(mass),金属钙的加入温度为850±10℃,金属钙的加入量为：2～3wt.%,发泡温度控制在为690±10℃,1000r/min的搅拌速度下,搅拌时间为1.00min～1.25min,保温时间2.50min左右。熔体发泡法中添加发泡剂过程实质为固体粒子与液体相混合的过程。颗粒的润湿性对泡沫的生成和稳定具有重要的影响。实验研究了氢化钛、氢化锆和铝合金的润湿行为。考虑到氢化物发泡剂高温分解过快问题,实验采用低温铝锗合金,在真空条件下,500-545℃温度范围内,采用改进的座滴法测量铝锗合金对氢化物发泡剂的接触角。考察了温度、合金中锗含量和接触时间对接触角的影响；采用XRD和SEM对润湿界面进行分析；结果表明铝锗合金滴在30s内润湿角呈现较大的变化,30s后润湿角即达到平衡。铝锗合金滴的润湿角随着温度表现良好的线性递增关系,对于TiH2,线性拟合方程为θTiH2=0.353℃-39.87；对ZrH2,线性拟合方程为θZrH2=0.22℃+28.3；润湿角随合金中Ge的含量表现出线性递减的趋势,对于TiH2,线性方程分别为θTiH2=214-200CGe(wt%);对于ZrH2,线性方程分别为θZrH2=198-163.5Ge(wt.%)。在实验设定温度范围内,ZrH2的润湿角均小于TiH2的润湿角,通过线性方程推测,在泡沫铝实验温度下,ZrH2的润湿能力要优于TiH2,因此在添加ZrH2或者TiH2后,ZrH2颗粒更容易分散到铝熔体中,形成均匀孔隙的泡沫铝材料。这可能是用ZrH2比TiH2作为发泡剂制备泡沫铝的均匀性更好的重要原因之一。界面研究结果表明,界面处除了液滴物理扩散外无合金化反应发生。对ZrH2比TiH2制备的闭孔泡沫铝材料进行了静态压缩实验研究,实验中发现,纯铝基闭孔泡沫铝材料在静态压缩过程中,均具有线弹性区、平台区和紧实区三个阶段,并显示出比较明显的塑性泡沫材料的特征；对闭孔泡沫铝的能量吸收性能进行了分析,从闭孔泡沫铝的能量吸收能力、能量吸收效率进行了详细的研究,结果表明：ZrH2制备的闭孔泡沫铝的能量吸收能力要大于TiH2制备基闭孔泡沫铝的能量吸收能力；纯铝基泡沫铝材料能量吸收效率最高可达90%；对纯铝基泡沫铝材料能量吸收图的研究发现,纯铝基闭孔泡沫铝材料作为缓冲吸能材料使用时,具有相当好的能量吸收能力。更多还原

【Abstract】 Aluminum foam is a new multi-functional materials consisting of metallic frame and bubble holes. It has an extensive application in different areas, including automotive, transportation, architecture, machinery, metallurgy, chemical engineering, communication and aerospace, due to its advantages such as, high strength, fire-resistance, sound and energy absorption, sound isolation, impact absorption and interception of electric wave. At present, tremendous research activities concerning aluminum foam have been implemented.Melt foaming method is one of the production ways of the aluminum foam, which make molten metal foaming by use of decomposition gas with blowing agent, and the gas was remained in the melt. Expansion of foam mainly was produced by decomposition of hydride hydrogen as a source of foam bubbles. The choice of the blowing agent is particularly crucial in the production of aluminum foam. In this paper, both laboratory of the direct foaming in melt method for fabricating pure aluminum matrix foam are investigated and discussed in details using of different blowing agent system, such as, rare earth hydride and ZrH2.The thermal decomposition behaviors of rare earth hydride were studied by using temperature-programmed thermogravimetry method. Result shows that rare earth hydride begin to show a substantial weight loss phenomenon when the temperature was above 760℃Rare earth hydride was easy to absorbent and become rare earth hydroxide, so to keep under seal. The thermal decomposition behaviors of ZrH2 and TiH2 were studied by using temperature-programmed thermogravimetry method. The DTA profiles were obtained at heating rates of 10,20,30,40 K/min respectively; The thermodynamics characteristic and potential reaction in the progress of foaming were analyzed; The effect of the hydride particles dispersion on foams aluminum was investigated in the alloy melt. Results indicated that decomposition behaviors of the hydride was controlled by chemical reaction process under low heating rate, On the contrary, controlled by diffusion controlled of solid product under high heating rate. The distributions of metal elements were impacted by thermal decomposition of hydride, the bubble of floating upward lead to the non-uniform distribution of the elements.Aluminum foams were fabricated by the melt-based route using the ZrH2 and rare earth hydride as blowing agent. The relationship between the cell structures and the processing parameters such as the amount of Ca, foaming temperature, foaming agent content, stirring time and holding time was studied. Based on the effects of processing parameters on cell structure that was tested by software image-pro plus, optimized fabricating processing scheme was obtained. Results indicated that The foaming agent (ZrH2) suit for preparation for small aperture aluminum foams with average pore diameter of 1-2 mm; The foaming agent (rare earth hydride) suit for preparation for big aperture aluminum foams; the mix of TiH2 and rare earth hydride suit for preparation for small aperture and uniformity aluminum foams. Control proper processing parameters were good for the acquirement of the aluminum foams which contains uniform cell structure of high porosity. To rare earth hydride, the best process parameters were as follows, rare earth hydride 2%-2.5%(mass), the temperature 750±10℃, stiring time 1.00min～1.25min, holding time 2.50min; To the mixture of foaming agent, the best process parameters were as follows, the contents of foaming agent 2%(mass), the ratio of rare earth hydride/TiH2 8.5/1.5～8.0/2.0, the temperature 730±10℃, stiring time 1.00min, holding time 3min; To ZrH2, the best process parameters were as follows, the contents of ZrH2 0.8%1～1.0%(mass), the adding temperature of Ca 850±10℃, the contents of Ca 2-3%(mass), the temperature 690±10℃, stiring time 1.00min～1.25min, holding time 2.5min;The adding foaming agent proces was essentially mixing process of solid particles and liquid phase. Particle wettability had an important impact on bubble formation and stability.Wettability was measured by Al-Ge alloy instead of purity aluminum that can decrease the temperature of experiment and reduce the loss of ZrH2 and TiH2 was as little as possible. Al-Ge alloy was prepared by induction furnace in vacuum at 800℃. The concentration of Ge in Al-Ge alloy was determined by phenylfluorenone cetyltrimethylammonium bromide spectrophotometry without separation or extraction atλ=512nm. The contact angle of Al-Ge alloy on the vesicant was mesured by the improved-sessile drop technique in vacuum in the temperature range of 500-545℃. The effects of temperature, concentrations of Ge in alloy and contact time on the measurement of contact angles were investigated. The microstructure of interface between the alloy and vesicant was examined by XRD and SEM. The parameters of thermodynamics and spreading kinetics of liquid Al-Ge alloy on the surface of TiH2 and ZrH2 were calculated at different condition. The contact angles of Al-Ge alloy on the surface of TiH2 and ZrH2 were investigated by the AUTO-CAD. The results showed that the wetting angle of Al-Ge alloy droplets showed a larger change in the 30s, and rapidly arrived in balance after 30s. The contact angles of TiH2 and ZrH2 decreased with increasing the temperature and increased with decreasing concentrations of Ge in alloy. Linear equations were as follows, to TiH2,θTiH2=0.353℃-39.87 andθTiH2=214-200CGe(wt%). To ZrH2, Linear equations were as follows,θzrH2=0.22℃+28.3 andθZrH2= 198-163.5Ge(wt.%). According to the result of XRD and SEM analysis, there was no reaction happened exceptthe physical droplet diffusion outside. The wettability of liquid Al-Ge alloy on the surface of TiH2 and ZrH2 was affected by the diffusion on the surface.The results showed that the contact angle of Al-Ge/ZrH2 was less than Al-Ge/TiH2. Uniformity of pore has been improved with the ZrH2 as vesicant compared to TiH2 that may be explained.Researches on static compressions of pure aluminum matrix foam have been conducted. Results showed that there were three compression processes.The compression curves of pure aluminum matrix foam were flat, indicating that more obvious characteristics of the plastic foam; apparently showing that more obvious characteristics of the brittleness foam. Energy absorption characteristic of closed-cell aluminum foam was systematically analyzed, with energy absorption capabilities ang efficiencies of aluminum foams were studied. The results showed that the energy absorption capability of foam aluminum with ZrH2 as bubble agent were more bigger than that of foam aluminum with ZrH2 as bubble agent under the same compressing condition; The energy absorption efficiency of foam aluminum could be as high as 90%; it is also found, from the energy absorption figure of foam aluminum, that pure aluminum matrix foam had goodish energy absorption capability and the maximal allowable stress as energy absorption material.更多还原