| Metal foam as a new type of structure and function of materials, has the characteristics of structure of the porous and the performance advantages of metal materials, its excellent performance such as lightweight, insulation and sound-absorbing, electromagnetic shielding and the shock absorption. It can be widely used in aerospace, petrochemical, construction, automotive and other fields involves separated by filtration, energy-absorbing shock absorption, electromagnetic shielding. The preparation process of the metal foam is mainly two kinds:powder metallurgy and melt foam. Melt foaming process is the most successful method of preparation of aluminum foam. TiH2powder has often been used as a blowing agent, but it is difficult to get a uniform pore structure, high-performance aluminum foam because of the decomposition speed is too fast, and the release of hydrogen is too short.In this study, a certain porosity metal foam has been successfully prepared by the two processes of powder metallurgy and melt foaming, and the pure Ni uniformly coated Ni/TiH2of composite powder has been successfully prepared by electroless plating. By means of optical microscope (OM), scanning electron microscopy (SEM), differential thermal analysis (DSC/TG), X-ray diffraction (XRD), the electronic energy dispersive spectroscopy (EDS), the impaction of sintering temperature on the morphology of sintered compacts was preliminary explored and the impaction of the particle size of pore-forming agent and the thickness of the compressed sample on porosity was investigated; electroless plating process of Ni/TiH2composite powder has been optimized by orthogonal test and single factor experiment; the growth mechanism and model of the coating were established and the morphology of the coating affected by activator concentration, electroless plating reaction time and reaction temperature has also been investigated; with composite powder successfully applied to the melt foaming process, a low density and high porosity and uniform pore structure, high-performance aluminum foam has been successfully prepared. The main conclusions are as follows:(1) The best sintering temperature of the foam zinc aluminum, which prepared by powder metallurgy process, is410℃(sintering3h insulation2h); under this temperature, the sintered body is close, more porosity and relatively uniform and there is a significant sintering neck; when the NaCl particle size of the pore-forming agent is greater than600μm, pore structure is extremely uneven and easy collapsed; when the thickness of green compacts within this range of3mm-5mm, the porosity of the green compacts increases with the decrease in the thickness of the green compacts.(2) By orthogonal test and univariate test, the optimal parameters of electroless nickel plating process are19G/L(hydrazine hydrate mass concentration),40g/L(the nickel sulfate mass concentration),9.5(the bath reaction pH),88℃(the reaction of the bath temperature),45min(the total reaction time), and0.1g/L(the concentration of the activating solution).(3) The Ni layer, which use the optimization of process by orthogonal experiments, is coated completely and its thickness is uniform, the average thickness of the coating was approximately1.5-2.0μm. The coating growth mechanism is in line with the Ostwald (Ostwald ripening) mechanism. According the curve of DSC+TG, composite powder of Ni/TiH2compared with the original TiH2powder, the reaction temperature of the release of hydrogen increased from490℃to580℃, increased by about90℃and significantly delayed the release of hydrogen is about80s.(4) Take the homemade Ni/TiH2composite powder as a blowing agent, the release time of hydrogen has been greatly postponed in the process of melt foaming. So, the high-performance aluminum foam with a low density and high porosity and uniform pore structure has been successfully prepared. Its density value is about0.16-0.35g/cm3and the porosity is up to85%.(5) The formation and growth mechanism of bubbles in the melt foaming process is in line with Ostwald (Ostwald ripening) mechanism. There are a lot of small formed at the first process. Continuously, small bubbles merged to form the aperture stable bubble. Lastly, large bubbles become larger and larger until the wall of bubbles rupture. |
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