【作者】 朱勇刚；

【导师】 陈锋；

【作者基本信息】 东南大学 ， 材料加工工程， 2004， 硕士

【摘要】 粉末冶金发泡法由于能够生产复杂形状的泡沫铝及泡沫铝芯三明治结构而成为泡沫铝研究领域的一个热点,本文对泡沫铝的粉末冶金制备工艺和压缩吸能性能进行了探索性的研究。测试了TiH2热分解曲线,发现松散的TiH2在氩气保护气氛下,420℃左右开始分解, 640℃左右达到峰值。确定了泡沫铝制备的主要工艺参数,合适的压力为150MPa以上,热压温度为450℃,纯铝的预设炉温为720℃,AlSi7的预设炉温为640℃。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及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。试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组织类似。泡沫铝的压缩、吸能性能研究表明:泡沫铝的压缩变形方式通过泡壁的弯曲和折叠完成,其应力-应变(σ~ε)曲线具有较长的屈服“平台”。随相对密度的降低,泡沫铝的屈服应力、弹性模量和吸能能力降低,吸能效率的峰值有所增加。更多还原

【Abstract】 Powder metallurgical foaming method becomes an important research aspect in the field of metallic foams, because it is specialized in manufacturing 3-dimensional net shape aluminium foam parts and sandwich structure. The present paper investigates the preparation techniques of aluminium foam by powder metallurgy method and their compression deformation and energy absorption properties. By testing the thermal decomposition curve of TiH2, it was found that incompact TiH2 powder in Ar began to decompose at about 420℃, and achieve peak value at about 640℃. It was ascertained that primary processing parameters include pressing stress, hot-pressing temperature and pre-set furnace temperature. The proper hot-press temperature and pressing stress were 450℃ and more than 150MPa respectively. The pre-set furnace temperature for pure Al and AlSi7 was 720℃ and 640℃ respectively. Evolution of pore morphology and cell wall microstructure of aluminum foam during powder metallurgical foaming was studied. It was found that aluminum foam shows three foaming stages during foaming, that is tiny expansion, remarkable expansion and shrinkage; and the pore morphology goes through three stages, that is nucleation and growth, merging and coarsening, and the porosity decreasing from the upper part of the foam to the lower part of the foam. The merging and porosity gradient of the pore structures were resulted from capillarity-driven and gravity-driven melt flow within the melt foam column. The silicon diffusing layer along the boundary of aluminum and silicon powders melts first during heating, and then the melt diffuses along the boundary of aluminum powders, resulting in the entire alloying between aluminum and silicon powders. The experiment shows that the solidified cell wall microstructures are similar to those of typical modified cast Al-Si alloys. It was shown by the experiments on the compressing and energy absorption behavior of aluminium foams that, the mode of aluminium foam compression and deformation was achieved by bending and puckering of cell wall; the compressive stress- strain (σ~ε) curve have a long collapse region. With the decrease of relatively density of aluminium foam, its elastic modulus, yielding stress and energy absorbing ability decrease, and the peak of energy absorption efficiency increases to some extent.更多还原