泡沫铝夹心板芯层泡沫结构的研究

研究了采用轧制复合-粉末冶金发泡法制备的泡沫铝夹心板的生产工艺,探讨了主要工艺条件对芯层泡沫结构的影响,得到了优化的工艺参数.研究结果表明:轧制复合工艺可以使芯层粉末达到很高的致密度,为发泡过程创造了有利条件.轧制复合板适宜的发泡温度为615～620℃,温度过高会导致芯层出现大尺寸连通孔.发泡时间对熔融态泡沫体的凝固过程有显著影响,时间过长会使泡沫层塌陷,发泡温度为620℃时,经4～6min发泡芯层可形成良好的泡沫结构.     

预氧化时间和温度对聚丙烯腈纤维预氧化的影响

通过在线监测聚丙烯腈(PAN)纤维在预氧化过程中热收缩行为,结合纤维预氧化前后性能变化,考察了时间和温度对预氧化的影响.实验结果表明:温度和时间作用不同,即温度作用不能用时间代替.温度在预氧化过程中起决定性作用,要得到较高的环化度,预氧化温度必须超过240℃.     

发泡工艺条件对聚酰亚胺泡沫结构的影响

研究了聚酰亚胺(PI)先驱体和发泡温度等工艺参数对PI泡沫结构的影响,采用DSC,TGA和光学显微镜对PI泡沫结构进行观察及表征.研究发现:先驱体的发泡温度应在150℃左右,随着发泡温度的升高,泡沫的密度降低;泡沫具有突出的开孔特性,开孔率高达93%以上;泡沫的密度主要取决于泡沫孔数和泡孔壁厚.     

基于气体捕捉法的泡沫Ti-6Al-4V等温发泡规律研究

为了确定气体捕捉法制备泡沫Ti-6Al-4V等温发泡过程中孔隙率和微观孔洞的变化规律,在不同发泡温度及发泡时间下制备了泡沫Ti-6Al-4V.运用阿基米德原理对泡沫Ti-6Al-4V的孔隙率进行测量,通过OM和SEM对其微观特征进行观察.研究表明:泡沫Ti-6Al-4V的孔隙率及孔径均随等温发泡温度升高而增加;但当发泡温度大于950℃时,孔隙率和孔径均减小,且孔洞形态由球形变成多边形,这是由于基体内生成大尺寸β相造成的.增加发泡时间能以促进孔洞长大的方式提高泡沫Ti-6Al-4V的孔隙率,球形孔洞数量随着发泡时间的增加逐渐增多.经950℃/10 h发泡得到了孔隙率34.2%、孔径平均值156μm、孔洞为球形且分布弥散的泡沫Ti-6Al-4V.     

预氧化对中间相沥青泡沫炭结构和性能的影响机制研究

研究了预氧化对萘系中间相沥青的表面化学性质、族组成分布以及对泡沫炭的发泡条件、泡孔形成、孔结构及微结构的影响机制.当中间相沥青经210℃预氧化2h后,其喹啉不溶物含量增加32.3%,族组成分布变窄.在600℃/3MPa发泡条件下,所制石墨化泡沫炭的平均孔径、压缩强度分别为200μm、2.8MPa.     

氧化处理对Ti2分解特性及组织结构的影响

针对制备泡沫铝异型件的熔体路径发泡先驱体二次发泡工艺,对TiH2的氧化处理、变温分解特性、等温分解特性、组织结构进行了研究.研究表明:氧化处理可有效提高发泡剂的开始分解温度,随氧化处理温度的提高,开始分解温度提高;氧化处理后发泡剂的等温分解曲线由低分解平台、快速分解阶段和稳定分解阶段3部分组成,低分解平台随氧化处理温度的提高而延长;400℃/6h+500℃/1h+620℃/30s的处理,可使TiH2的分解量较400℃/6h+500℃/1h处理时有所提高;TiH2氧化处理后在其表面生成了厚约1.1~1.5μm的TixOy致密氧化层,TiH2在300~550℃氧化,其物相依次变化为:TiH1.97—TiH1.97+TiO2—TiH+TiO+TO—TiH+TiO+TO+TiH.     

孔结构对通孔泡沫铝水声吸声性能的影响

测试了不同孔结构通孔泡沫铝样品在 3～ 2 4kHz频段内的水声吸声系数。试验结果表明 :不同孔结构的通孔泡沫铝都具有较好的水声吸声性能 ,其水声吸声性能与其孔结构密切相关。当孔径减小 ,孔隙率和厚度增大时 ,水声吸声性能增高     

发泡剂含量对双马来酰亚胺泡沫泡孔结构和性能的影响

以偶氮二甲酰胺(AC)为发泡剂,采用预聚、发泡的两步法制备双马来酰亚胺泡沫,研究AC含量对泡沫泡孔结构、密度、尺寸稳定性温度和压缩性能的影响。结果表明:可通过发泡剂用量的改变实现泡沫密度在60~280kg/m3范围内调整,发泡剂用量对泡孔尺寸及其均匀性影响较小。随发泡剂用量降低,尺寸稳定性温度和压缩性能提高,当泡沫密度为280kg/m3时,尺寸稳定性温度可达220℃,压缩强度和模量分别为4.8MPa和200MPa,满足结构泡沫的耐温性能和力学性能要求。     

钝化液温度对铝阳极氧化膜性能的影响

对铝及其合金进行钝化处理是提高其耐蚀性的有效手段.研究了工业纯铝普通阳极氧化膜在不同温度钝化液(Alsur408)条件下处理的表面形貌、组织结构、厚度和耐腐蚀性规律.结果表明,阳极氧化的工业纯铝氧化膜表面有均匀的纳米级孔洞,经不同条件钝化后,在氧化膜表面生成钝化膜,厚度约为1μm;随着钝化温度增加,钝化膜逐渐增厚,表面形貌致密平整;当钝化液温度高于50℃时,表面裂纹明显,耐腐蚀性表现为先增强后减弱;当钝化液温度为40℃时,钝化膜表面平整致密,无微裂纹,自腐蚀电位为0.1V,耐腐蚀性最高.     

镁的添加对制备泡沫铝夹芯板泡孔稳定性的影响

通过粉末-铝板复合轧制方法制备出一种界面为冶金结合的泡沫铝夹芯板.分别采用对发泡剂的处理和添加Mg元素的方法来提高芯材泡沫的稳定性.研究发现只有同时对发泡剂处理以及添加Mg元素才能够提高泡沫的稳定性.研究了此种方法中重要的泡沫稳定机制,Mg元素的添加改善了铝硅合金粉末原料生产过程中产生的氧化物颗粒在孔壁上的润湿性,使氧化物颗粒嵌入孔壁中,阻碍了孔壁上金属排液现象的产生,有效的起到稳定泡孔的作用.     

Effect of cell shape anisotropy on the compressive behavior of closed-cell aluminum foams

The closed-cell Al–Si foams have been prepared by molten body transitional foaming process using TiH₂ foaming agent. The cell shape anisotropy ratio of specimens with various relative densities was measured. The quasi-static compressive behavior of Al–Si foams in both longitudinal and transverse directions were investigated. The results show that Al–Si foam loaded in the transverse direction exhibits a lower stress drop ratio. The relationship between plastic collapse stress ratio and cell shape anisotropy is in accordance with Gibson and Ashby model. The plastic collapse stress and the energy absorption property of Al–Si foams increase following power law relationship with relative density. Moreover, Al–Si foams exhibit higher plastic collapse stress and the energy absorption property in the longitudinal direction than that in the transverse direction.     

Effect of TiH2 particle size distribution on aluminum foaming using the powder metallurgy method

TiH₂ decomposes over a range of temperatures strongly influenced by diverse factors including particle size. In the present research, a systematic study of the dehydrogenation behavior of TiH₂ powder of different particle size distribution was undertaken with the aid of thermogravimetric analysis. The effect of this parameter on aluminum foaming was evaluated. It was found that when TiH₂ exceeds a critical particle size (around 50 μm), dehydrogenation occurs as a single desorption event with onset temperatures around 500 °C. The reduction of particle size, besides reducing the onset of hydrogen release, decreases the dehydrogenation rate. As a result, the first dehydrogenation event gets sharper and tends to overlap with the second with increasing particle size. The use of selected powders on foaming showed that the final foam expansion and porosity features, such as pore size, pore density, and homogeneity are largely influenced by the particle size distribution of the foaming powder. TiH₂ of the largest particle size was the most suitable for foaming pure aluminum.     

Investigation and characterisation of aluminium alloy foams with TiH2 as a foaming agent

This article presents an account of experiments used to produce aluminium alloy foams by the melt route process using titanium hydride as a foaming agent. Powdered titanium hydride with content of 0.4–1.4% (mass fraction) was added to the molten pure aluminium and the foaming condition was controlled at 690°C (1274°F). In the process, homogeneous aluminium foams were produced with a calcium amount of 1.0–3.0% (mass fraction). The mechanical properties of the aluminium foams with diverse relative density were tested. The result indicates that the foaming agent is suitable for making small aperture aluminium foams with an average pore diameter of 1.2?mm.     

中间相沥青的预氧化对石墨化泡沫炭微裂纹的影响

通过对萘系中间相沥青进行预氧化处理,研究族组成变化对石墨化泡沫炭微结构的影响机制。结果表明:中间相沥青经过预氧化处理后,喹啉不溶物含量提高、族组成分布变窄,导致石墨化过程中泡沫炭泡孔的孔壁、韧带处热应力的梯度差异变小,进而使得微裂纹的数量、长度及间隙减小。     

Elastic and electric properties of closed-cell aluminum foams: Cross-property connection

Foamed aluminum (AlMg1Si0.6) in the porosity range 0.45–0.85 produced by the powder metallurgy method is analyzed with regard to its elastic and electric properties. Various predictive models for the electrical conductivity and Young's modulus of closed-cell metal foam are assessed based on the experimental measurements. It is shown that the differential scheme provides the best predictions of the electrical conductivity in the porosity range 0.7–0.85, while Mori–Tanaka's scheme gives the best results for the Young's modulus. Comparing the two sets of the experimental data, cross-property coefficient that connects changes in the Young's modulus and electrical conductivity of a material due to pores was determined. A non-trivial finding is that the best prediction of the cross-property coefficient is obtained in the framework of non-interaction approximation.     

发泡温度对炭泡沫结构及性能的影响

以AR中间相沥青为原料,采用中间相沥青自发泡法在初始发泡压力为3MPa、发泡温度在390～450℃范围内制备了4种炭泡沫。利用SEM观察了炭泡沫的孔隙结构,并测定了其体积密度、抗压强度和导热系数,考察了发泡温度对炭泡沫结构及性能的影响。结果表明,采用较低的发泡温度(430℃)可以消除大的孔隙缺陷;当发泡温度为410℃时,炭泡沫导热系数最高,为0.256W/(m·K)。     

Effect of melt treatment on microstructure and impact properties of Al-7Si and Al-7Si-2.5Cu cast alloys

The microstructures and impact toughness of Al-7Si and Al-7Si-2.5Cu cast alloys were studied after various melt treatments like grain refinement and modification. The results indicate that combined grain refined and modified Al-7Si-2.5Cu alloys have microstructures consisting of uniformly distributed α-Al grains, interdendritic network of fine eutectic silicon and fine CuAl₂ particles in the interdendritic region. These alloys exhibited improved impact toughness in as cast condition when compared to those treated by individual addition of grain refiner or modifier. The improved impact toughness of Al-7Si-2.5Cu alloys are related to breakage of the large aluminum grains and uniform distribution of eutectic silicon and fine CuAl₂ particles in the interdendritic region resulting from combined refinement and modification. This paper attempts to investigate the influence of microstructural changes in the Al-7Si and Al-7Si-2.5Cu cast alloys by grain refinement, modification and combined action of both on the impact toughness.     

Microstructure evolution and decomposition behavior of an novel core-multi-shell structure TiH2 foaming agent

Al foams have received an increasing attention due to their light weight, high specific strength, energy absorption, sound absorption, damping and electromagnetic shielding. However, the issue of low mechanical property is still a challenge due to the mismatch between the melting point of Al and Al alloys and the decomposition temperature of TiH₂ blowing agent. In this work, an novel TiH₂ foaming agent with core-multi-shell structure (TiH₂/Ti₃O@TiO₂/BPR) was prepared by thermal oxidation and coating boron phenolic resin (BPR) treatment. The results showed that the composite layers of Ti₃O@TiO₂ with a thickness about 70 nm and BPR with a thickness about 200 nm were formed on the surface of TiH₂ particles which can act as an excellent thermal and diffusional barrier to retard the heat transfer and delay the release of hydrogen. Compared with as-received and pre-oxidized TiH₂ particles, TiH₂/Ti₃O@TiO₂/BPR particles exhibited an excellent slow release property and its peak temperature of hydrogen release and corresponding time are about 647 °C and 1801 s, which increased by about 83 °C and 176 s, 44 °C and 59 s, respectively. The hydrogen release temperature matched well with the melting point of Al and Al alloys, which is very suitable for preparing high quality Al foams.     

Effect of homogenizing heat treatment on the compressive properties of closed-cell Mg alloy foams

Closed-cell AZ31 Mg alloy foams were successfully prepared by melt-foaming method. Homogenizing heat treatment was applied on the foams and the effects of heat treatment on compressive properties of closed-cell Mg alloy foams were investigated systematically. The results showed that homogenizing heat treatment enhanced the compressive properties in terms of yield strength, mean plateau strength, available energy absorption capacity and ideality energy absorption efficiency of the foams. In addition, homogenizing heat treatment greatly reduced the stress drop rates of the foams. Specimens homogenized at the temperature of 753 K for 24 h possessed good combination of yield strength, compressive stability, available energy absorption capacity and ideality energy absorption efficiency under the present experiment conditions. And the reasons were discussed.     

Fabrication and characterization of closed-cell aluminum foams with different contents of multi-walled carbon nanotubes

Closed-cell aluminum foams with different contents of multi-walled carbon nanotubes (MWCNTs) were fabricated by using modified melt foaming method. In order to effectively disperse MWCNTs, orthogonal tests were utilized to determine the optimal ball-milling parameters. The existence forms of MWCNTs in aluminum foams and the compressive properties of the foams were investigated. Considered from the dispersion degree and structural changes of MWCNTs, the optimal parameters were obtained, the parameters mainly referred to weight ratio of MWCNTs to aluminum powder, weight ratio of ball to powder, milling rate and milling time, respectively. The results showed that MWCNTs mainly existed in three forms: totally embedded in cell wall, partly embedded in cell wall and totally exposed on cell wall surface, respectively. The reasons were mainly due to the existence of defects and amorphous carbon on the surface of MWCNTs, which promoted the wettability between the aluminum matrix and MWCNTs. In addition, with the MWCNT content increasing, the yield strength, structural stiffness and energy absorption capacity of the foams increased first and then decreased. Meanwhile, under the present conditions the foams with MWCNT content of 0.5% possessed the optimal comprehensive mechanical properties and the reasons were discussed.