Study On Preparation Of Aluminium Foam By Powder Metallurgy Method And Its Properties

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.