| Foamed pure aluminium and various foamed aluminium alloys are a kind of novel light-weighted functional materials characteried by mass holes dispersed in the parent material. In this thesis two techniques, powder metallurgy and melt foaming for fabricating foamed aluminium and aluminium alloys, were mainly studied.Regarding the fabrication of foamed aluminum by powder metallurgy, the influence of pressing and sintering processes on the foaming of aluminium were investigated; the dynamics during the sintering process was also analyzed. By investigating the effects of foaming process parameters on the porosity and structure, we have obtained the optimized process as follows: Firstly press the powder under a pressure of 350MPa, then sinter for 40 minutes in the air atmosphere at 400℃and press again at 150MPa, at last, foam for 12 minutes at 720℃. The best foaming-agent dosage is 2wt%. This leads to the fabrication of foamed aluminium that has a well-proportioned structure with a porosity of 80%.In the melt foaming process, on the other hand, aluminium powder within the granule size of 74~150μm was used for melt thickening through the increases in viscidity of the melt aluminium and stabilization of the gas that was formed from the decomposition of the foaming-agent. The influence of mixing time, foaming temperature, foaming-agent dosage and the amount of aluminium powder on the porosity and the pore structure was investigated. According to these results, the pore size can be changed under control only by changing the dosage of aluminium powder while other parameters were kept the optimized values. The optimized processing conditions are: Aluminium powder dosage of 5~15%wt%, blended for 7 min at 650℃, foaming agent dosage of 1.5wt%. Using this technics, foamed AlSi7Mg0.45 alloy with well structure, porosity within 80~85% and pore size within 2.0~8.5mm was fabricated.The dynamics of nucleation and growth of the pores during the foaming process was conducted. The effectual pore sizes range in the melt aluminium in case of heterogeneous and homogeneous nucleation were deduced respectively, also the relation between the radius r of the pore and foaming time t was carried out, by which the maximum size of sphere pore was calculated.According to the experiment results of the different pore sizes obtained in the melt foaming process, the viscidity of the aluminium melt after adding aluminium powders was found to be close to that of mine slurry and belonged to the non-Newtonian fluid. The viscidity of which can be expressed by formula"Vand". The theoretic formula of the pore size was amended to the expressions appropriate for the melt foaming process in which aluminium was added to increase the viscidity.Mechanical property testing revealed that the compressive stress-strain of the foamed AlSi7Mg0.45 went through three phases including linear elastic zone, platform zone and the densifing zone. The relation between stress and strain in every stage can be well described by the Ashby model.Based on the stress-strain curves, the energy absorption capability was calcultaed. It was found that, under the same strain, the energy absorption capability decreases with the decreases of density. However with increasing strain, the energy absorption efficiency of foamed metal increases initially and then decreases. The lower the density, the longer the plateau line is. The energy absorption efficiency is over 80% within the platform zone.Three models for different foamed aluminium were established, i.e., model I for unhomogenous structure, model II for homogenous structure and model III for defected structure with huge poruses. The formulas of the elastic modulus for different models was obtained via Finite Element Simulation with ANSYS software.Finally, according to the experiment and simulation results, Finite Element simulations of the bumper made from round metal tube filled with three kinds of foamed AlSi7Mg0.45, the densities of which are 0.38g/cm3,0.56g/cm3,0.73g/cm3 and hollow tube were carried out on ANSYS/LS-DYNA. The simulation results showed that the bumper made from round metal tube filled with foamed AlSi7Mg0.45 is much lighter than that made from traditional hollow metal tube, as well as the number of the metal tube and the volume is greatly reduced. Among these three bumpers of different densities, the one filled with foamed AlSi7Mg0.45 with the density of 0.56g/cm3 had the best performance. Compared to the hollow metal tube bumper, the weight and volume were reduce by 34% and 57% respectively.
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