Structural Characterisation of Malallic Foam Produced by P/M Method

从刚性轻量化结构和吸声、吸冲击能、电磁屏蔽和减振等方面的功能效率的角度来看，多孔金属都引起了人们的兴趣。本课题研究了泡沫多孔铝的粉末冶金工艺。结果表明：1)自由膨胀法制备的泡沫铝胀形过大，胀形表面粗糙度较大，胀形表面存在微裂纹。在膨胀过程中使用钢套来限制压坯的胀形，既可以有效地提高表面质量，又可以通过防止产生的气体泄漏来实现泡沫产品的更高孔隙率。2)确定了生产极低表观密度泡沫铝的最佳发泡条件：发泡温度和发泡剂的添加量是控制孔隙率和孔结构的最重要因素。可浮性泡沫铝可以通过控制泡沫铝的孔结构为闭孔结构来制备。3)通过对图像的分析可知，与传统的液相法相比，P/M法的细胞结构均匀性得到了很大的改善。通过P/M过程获得的细胞结构与Voronoi细胞惊人地相似。5)可发泡珠和/或丝可用于形状复杂的发泡金属件的膨胀成型。

Cellular metals are of interest both from the viewpoint of stiff lightweight structures and theire functional efficiencies in sound absorption, impact energy absorption, electromagnetic shielding and vibration damping. In the present project, a powder metallurgical technique for the production of foamed cellular aluminum has been studied. Obtained results are as follows :1) The foamed aluminum produced by free expansion usually shows excessive bulging which is accompanied with a rather large surface roughness and micro-cracks on its bulged surface. A use of a steel sleeve to restrict the bulging of the compacts during expansion is effective both to improve the surface quality and to achieve a higher porosity of the foamed products by preventing the evolved gas to leak.2) Optimum foaming conditions to produce aluminum foams with very low apparent densities are established : the foaming temperature and the addition of the foaming agent are of most important to controll both the porosity achieved and the cellular structure. Floatable aluminum foam can be produced by controlling its cell structure as closed one.3) It is determined from the image analizing study that the homogeneity of the cellular structures is much improved by the P/M process as compared with the conventional liquid process.4) The cellular structures obtained by the P/M process bear a striking resemblance to the Voronoi's cell.5) Foamable beads and/or wires are abvailable for expanding forming of foamed melallic parts with complex shape.