泡沫铝两步法制备工艺用新型发泡剂的热分解行为

研究一种适于两步法制备泡沫铝工艺用新型发泡剂的热分解行为,分析其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存在的反应。研究表明:该新型发泡剂具有分解温度范围宽、分解过程缓慢的特点;其在熔体中的发泡过程主要受化学反应控制;新型发泡剂所释放的氧化性气体与熔体发生反应,在气泡表面所形成的连续氧化膜,对稳定气泡形貌、减缓气泡的合并和长大有重要作用;该新型发泡剂在两步发泡法制备泡沫铝过程中表现出前期损耗率低、后期发泡效率高的优异性能。     

气泡在铝熔体中运动特性的数值模拟研究

利用Fluent数值模拟软件,采用VOF技术进行气体与液体之间的界面追踪,通过引入源项处理泡沫铝发泡过程中发泡剂的分解,对液态铝熔体中单气泡、双气泡及气泡群的运动特性进行模拟计算,得到表面张力及熔体粘度对气泡运动特性的影响。结果表明,上、下分布的气泡升浮过程中容易合并成单个气泡,且气泡合并引起的剧烈扰动加剧了气泡的变形和破碎;水平并列的双气泡升浮过程中,形成的一对乃至两对流体漩涡会推离两个气泡,中心距越来越远。熔体粘度增大,气泡群逸出速度减慢,但同时气泡有充足的时间合并长大。表面张力增大,气泡不易变形,制备的泡沫铝气泡更为圆整。     

熔体发泡法制备泡沫铝过程中无泡层的形成与控制

对熔体发泡法制备泡沫铝过程中无泡层的形成与控制进行研究,考察熔体中加入金属镁后的表面张力以及镁的加入对无泡层厚度的影响,结果表明：泡沫铝制备过程中无泡层的形成分为3个阶段,第一阶段为发泡初期短时间内形成,在这个过程中,气泡向上运动,部分液体残留在底部形成无泡层;第二阶段和第三阶段为气泡长大过程,由于液膜液体与Plateau边界处处存在压力差,促使液膜处的液体流向Plateau边界处,最后通过Plateau通道流向底部形成无泡层;向加入3%Ca（质量分数）的纯铝熔体中再加入0.5%Mg后,熔体的表面张力显著降低,泡沫体中无泡层的厚度得到很好的控制。     

泡沫铝发泡初期孔隙及气泡的形成与扩展

通过采用粉体致密化浸入式快速加热新工艺制备泡沫铝技术，研究了泡沫铝发泡早期气泡形成特征、早期气泡孔径结构特点及动态变化规律。结果表明：泡沫铝发泡历经以微膨胀、显著膨胀和塌陷收缩为特征的3个主要阶段；在发泡初期，微膨胀形成的机制主要是TiH2分解的H2，并受其受力状态所决定的，由此形成的裂纹式孔隙主要在固态，扩展方向呈横向特征。预制块的显著膨胀主要是由于TiH2的持续分解使裂纹式孔隙扩展长大的结果。由于新工艺加热升温迅速，发泡时间由一般的10min缩短为30—150s，使预制块固液态转换时间大大缩短，有效地提高了均匀发泡的动力学条件，同时还提高了TiH2的利用率。     

泡沫铝制备工艺的改进及关键问题探讨

对熔体发泡法制备闭孔泡沫铝的工艺进行了改进,并研究了发泡过程中TiH2加入量和粒度对泡沫铝孔隙率的影响。改进后的泡沫铝生产工艺在工业化生产方面具有很好地推广价值,主要体现在连续性生产和能源综合利用方面。试验证实：随着TiH2加入量增加,泡沫铝孔隙率不断增加;随着TiH2粒度的加大,孔隙率先逐渐减小后增加。     

粉末冶金发泡时泡沫铝孔结构及泡壁的微观组织演变

研究了粉末冶金法制备泡沫铝时泡沫孔结构及胞壁微观组织变化的规律.泡沫铝发泡时经历微膨胀、显著膨胀和收缩等过程;孔结构经历了形核和长大,以及在毛细力和重力驱动下泡壁熔体的流动引起的合并粗化和孔隙率自上而下梯度减小等演化过程.加热时,铝/硅颗粒边界处硅的扩散层首先熔化,并沿着铝颗粒边界扩散,最终使铝硅粉末复合体完全熔化而实现合金化.实验发现泡壁的凝固组织与典型的变质处理后的铸造铝硅合金的组织类似.     

以TiH_2为发泡剂制备泡沫铝的研究现状

探讨了发泡剂发泡法、粉末冶金发泡法、累积叠轧焊法中以TiH2为发泡剂制备泡沫铝的研究进展.在发泡剂发泡法中,对TiH2发泡剂高温下分解过快问题采取了热处理、化学改性、包覆等方法以减缓其释气速率,使泡沫铝生产易于控制;在粉末冶金发泡法、累积叠轧焊法制备泡沫铝夹心板的过程中,后者更有利于TiH2发泡剂的均匀分布.     

采用新型发泡剂制备泡沫铝

研究了一种在泡沫铝制备过程中可替代TiH2及ZrH2类发泡剂的新型发泡粉末的热分解行为,探讨该新型发泡剂加入量及发泡温度等因素对泡沫铝孔隙率的影响。研究表明:该新型发泡材料具有分解温度范围宽及分解过程缓慢的特点。当采用该发泡剂时,泡沫铝制备过程无需额外加入金属Ca类增粘剂;随发泡温度的升高,泡沫铝的孔隙率先升高后下降;随发泡剂量的增多,发泡体中的无泡层逐渐减少,当发泡剂的加入量在1.40%以上时,发泡体中的无泡层消失;在发泡温度740℃、发泡剂加入量1.40%~2.20%、搅拌时间3min、保温发泡时间5min的条件下,可以制备出孔径2~5mm,孔隙率60%~80%,孔隙基本均匀且无实心体的泡沫铝。     

TiH_2颗粒在铝熔体中的分散性模拟

发泡剂TiH2颗粒在铝熔体中的分布是决定泡沫铝孔结构和性能的重要因素。利用Fluent软件对TiH2颗粒在铝熔体中的分散性进行了数值模拟,重点考察了搅拌叶片参数和搅拌速度对TiH2颗粒在铝熔体中分散性的影响。结果表明,TiH2颗粒的分散均匀性受铝熔体的径向及轴向流动的影响,与搅拌叶片参数和搅拌速度有关;当搅拌叶片层数为3、叶片长度为30cm、叶片倾斜角θ=30°、搅拌速度为50r/s时,铝熔体中TiH2颗粒的分布均匀性最好。     

熔体注气法与熔体发泡法制备泡沫铝的压缩性能研究

比较研究了熔体注气法与熔体发泡方法制备的闭孔泡沫铝性能和组织结构。压缩试验表明,相同密度下,熔体发泡法制备的泡沫铝性能优于熔体注气法。相应的SEM观察表明,熔体注气法制备的泡沫铝泡孔表现为多面体形状,SiC颗粒密度高,泡孔壁薄、褶皱多。冶金组织复杂,氧化明显,表现出明显的脆性。熔体发泡法制备的泡沫铝孔洞形状为球形,孔壁较厚,泡壁相对平整、结构完整。因孔洞结构和组织结构差异导致2种方法制备的泡沫铝材料压缩性能差异明显。     

SiCP增强泡沫铝基复合材料的制备工艺研究

将SiC颗粒增强铝基复合材料的制备技术与泡沫铝熔体发泡技术相结合,探索了制备SiC颗粒增强泡沫铝基复合材料的工艺方法。讨论了SiC颗粒与铝基体之间存在的润湿性,界面反应以及SiC颗粒在熔体中沉降等问题,通过选择合适的合金成分,对SiC颗粒进行预处理,采用特定的搅拌和发泡等一系列工艺方案成功地予以解决。在熔体发泡过程中,通过严格控制发泡温度、搅拌速度和搅拌时间等工艺参数,制得了孔隙率基本可调,SiC颗粒和孔洞分布均匀的泡沫铝样品。     

Prediction of melt residual in batch type gas injection foaming process

In the batch type gas injection foaming process, there must exist some melt residual. A differential equation relating the particle content and gas injection depth in the batch type process was presented, by which the melt residual ratio was predicted with the stability criterion as the boundary condition. It was found that the particle diameter increased during the foaming process but the thickness of the foam cell wall can be regarded as a constant. The adsorption coefficient and the injection depth were found to have an inverse relationship, with an exponential of −0.89. Based on the adsorption coefficient at different injection depth, the residual ratio of the melt containing given size particles was able to be predicted. To decrease melt residual needs to increase the particle content and the initial injection depth, and the particle diameter and the critical coverage ratio should be decreased.     

THE STRUCTURE CONTROL OF ALUMINUM FOAMS PRODUCED BY POWDER COMPACTED FOAMING PROCESS

A new technique, powder compact foaming process for the production of aluminum foams has been studied in this article. According to this method, the aluminum powder is mixed with a powder foaming agent (Till2). Subsequent to mixing, the powder blend is hot compacted to obtain a dense semi-finished product. Upon heating to temperatures within the range of the melting point, the foaming agent decomposes to evolve gas and the semi-finished product expands into a porous cellular aluminum. Foaming process is the key in this method. Based on experiments, the foaming characteristics were mainly analyzed and discussed. Experiments show that the aluminum-foam with closed pores and a uniform cell structure of high porosity can be obtained using this method by adjusting the foaming parameters: the content of foaming agent and foaming temperature.     

Effect of Fly Ash Particles on the Compressive Properties of Closed-Cell Aluminum Foams

The closed-cell aluminum foam reinforced by 1.5 and 3.0 wt.% fly ash particles were manufactured by molten body transitional foaming process. The backscattered electron image shows that fly ash particles distribute uniformly in the cell wall. The quasi-static compression tests were conducted. Results show that Al/Fly ash foams have stable compressive property and the sudden stress drop was not observed. The plateau stress increases nearly linearly with relative density. Moreover, the addition of fly ash particles improves the plateau stress. Also, the energy absorption property of Al/Fly ash foams increase with relative density and fly ash content. These can be attributed to the contribution of the compression of cell gas and the membrane stress in the cell wall.     

陶瓷颗粒增强泡沫铝材料的研究

选用粉煤灰作为增强相,经X射线衍射分析,粉煤灰中主要成分为石英和莫来石,是一种坚硬的陶瓷颗粒。这种陶瓷颗粒起到了增粘作用,并且还有利于提高气泡的稳定性。将粉煤灰加入到熔融铝液中,经适当搅拌后,再加入发泡剂,经冷却,即可得到颗粒增强泡沫铝。利用粉煤灰颗粒增黏的泡沫铝与利用钙增黏的泡沫铝进行压缩强度性能检测。结果表明:粉煤灰不但有增黏作用,还由于石英与铝液发生原位反应生成的氧化物,以及粉煤灰中原有的莫来石起到颗粒增强作用。     

含FeO熔渣的起泡过程及起泡参数间关系分析

对ＣａＯ－ＳｉＯ２－Ａｌ２Ｏ３－ＦｅＯ熔渣在石墨还原过程中的起泡行为的分析表明，熔渣的起泡率受渣中气体的产生速度及熔渣的起泡指数影响；熔渣的起泡指数随渣中气泡直径的增大而减小；随熔渣碱度的减小，泡沫渣的平均寿命延长，泡末化愈稳定。     

Modeling nucleation and growth of bubbles during foaming of molten aluminum with high initial gas supersaturation

An idealized nucleation and growth based model was used to predict bubble size distribution in liquid aluminum foam, based on the assumption that the entire quantity of hydrogen added as TiH₂ was retained in solution initially. The model considered simultaneous nucleation and growth of bubbles in the first stage, and pure bubble growth in the second stage. Bubble nucleation was found to be feasible only heterogeneously within narrow crevices in non wetting substrates. Effects of initial gas supersaturation on total expansion, final bubble size distribution, total number of bubbles, and average bubble size were investigated. Model predictions of foam characteristics were compared with experimental observations on foams prepared by dissociating TiH₂ foaming agent in liquid aluminium, and good match between the two was found with respect to average cell size and total number of bubbles. Differences between model predictions and experimental observations, especially in the nature of bubble size distribution, and limitations of the model were explained.