Preparation Of Al Foam Using Rare Earth Hydride And Zirconium Hydride

Aluminum foam is a new multi-functional materials consisting of metallic frame and bubble holes. It has an extensive application in different areas, including automotive, transportation, architecture, machinery, metallurgy, chemical engineering, communication and aerospace, due to its advantages such as, high strength, fire-resistance, sound and energy absorption, sound isolation, impact absorption and interception of electric wave. At present, tremendous research activities concerning aluminum foam have been implemented.Melt foaming method is one of the production ways of the aluminum foam, which make molten metal foaming by use of decomposition gas with blowing agent, and the gas was remained in the melt. Expansion of foam mainly was produced by decomposition of hydride hydrogen as a source of foam bubbles. The choice of the blowing agent is particularly crucial in the production of aluminum foam. In this paper, both laboratory of the direct foaming in melt method for fabricating pure aluminum matrix foam are investigated and discussed in details using of different blowing agent system, such as, rare earth hydride and ZrH2.The thermal decomposition behaviors of rare earth hydride were studied by using temperature-programmed thermogravimetry method. Result shows that rare earth hydride begin to show a substantial weight loss phenomenon when the temperature was above 760℃Rare earth hydride was easy to absorbent and become rare earth hydroxide, so to keep under seal. The thermal decomposition behaviors of ZrH2 and TiH2 were studied by using temperature-programmed thermogravimetry method. The DTA profiles were obtained at heating rates of 10,20,30,40 K/min respectively; The thermodynamics characteristic and potential reaction in the progress of foaming were analyzed; The effect of the hydride particles dispersion on foams aluminum was investigated in the alloy melt. Results indicated that decomposition behaviors of the hydride was controlled by chemical reaction process under low heating rate, On the contrary, controlled by diffusion controlled of solid product under high heating rate. The distributions of metal elements were impacted by thermal decomposition of hydride, the bubble of floating upward lead to the non-uniform distribution of the elements.Aluminum foams were fabricated by the melt-based route using the ZrH2 and rare earth hydride as blowing agent. The relationship between the cell structures and the processing parameters such as the amount of Ca, foaming temperature, foaming agent content, stirring time and holding time was studied. Based on the effects of processing parameters on cell structure that was tested by software image-pro plus, optimized fabricating processing scheme was obtained. Results indicated that The foaming agent (ZrH2) suit for preparation for small aperture aluminum foams with average pore diameter of 1-2 mm; The foaming agent (rare earth hydride) suit for preparation for big aperture aluminum foams; the mix of TiH2 and rare earth hydride suit for preparation for small aperture and uniformity aluminum foams. Control proper processing parameters were good for the acquirement of the aluminum foams which contains uniform cell structure of high porosity. To rare earth hydride, the best process parameters were as follows, rare earth hydride 2%-2.5%(mass), the temperature 750±10℃, stiring time 1.00min～1.25min, holding time 2.50min; To the mixture of foaming agent, the best process parameters were as follows, the contents of foaming agent 2%(mass), the ratio of rare earth hydride/TiH2 8.5/1.5～8.0/2.0, the temperature 730±10℃, stiring time 1.00min, holding time 3min; To ZrH2, the best process parameters were as follows, the contents of ZrH2 0.8%1～1.0%(mass), the adding temperature of Ca 850±10℃, the contents of Ca 2-3%(mass), the temperature 690±10℃, stiring time 1.00min～1.25min, holding time 2.5min;The adding foaming agent proces was essentially mixing process of solid particles and liquid phase. Particle wettability had an important impact on bubble formation and stability.Wettability was measured by Al-Ge alloy instead of purity aluminum that can decrease the temperature of experiment and reduce the loss of ZrH2 and TiH2 was as little as possible. Al-Ge alloy was prepared by induction furnace in vacuum at 800℃. The concentration of Ge in Al-Ge alloy was determined by phenylfluorenone cetyltrimethylammonium bromide spectrophotometry without separation or extraction atλ=512nm. The contact angle of Al-Ge alloy on the vesicant was mesured by the improved-sessile drop technique in vacuum in the temperature range of 500-545℃. The effects of temperature, concentrations of Ge in alloy and contact time on the measurement of contact angles were investigated. The microstructure of interface between the alloy and vesicant was examined by XRD and SEM. The parameters of thermodynamics and spreading kinetics of liquid Al-Ge alloy on the surface of TiH2 and ZrH2 were calculated at different condition. The contact angles of Al-Ge alloy on the surface of TiH2 and ZrH2 were investigated by the AUTO-CAD. The results showed that the wetting angle of Al-Ge alloy droplets showed a larger change in the 30s, and rapidly arrived in balance after 30s. The contact angles of TiH2 and ZrH2 decreased with increasing the temperature and increased with decreasing concentrations of Ge in alloy. Linear equations were as follows, to TiH2,θTiH2=0.353℃-39.87 andθTiH2=214-200CGe(wt%). To ZrH2, Linear equations were as follows,θzrH2=0.22℃+28.3 andθZrH2= 198-163.5Ge(wt.%). According to the result of XRD and SEM analysis, there was no reaction happened exceptthe physical droplet diffusion outside. The wettability of liquid Al-Ge alloy on the surface of TiH2 and ZrH2 was affected by the diffusion on the surface.The results showed that the contact angle of Al-Ge/ZrH2 was less than Al-Ge/TiH2. Uniformity of pore has been improved with the ZrH2 as vesicant compared to TiH2 that may be explained.Researches on static compressions of pure aluminum matrix foam have been conducted. Results showed that there were three compression processes.The compression curves of pure aluminum matrix foam were flat, indicating that more obvious characteristics of the plastic foam; apparently showing that more obvious characteristics of the brittleness foam. Energy absorption characteristic of closed-cell aluminum foam was systematically analyzed, with energy absorption capabilities ang efficiencies of aluminum foams were studied. The results showed that the energy absorption capability of foam aluminum with ZrH2 as bubble agent were more bigger than that of foam aluminum with ZrH2 as bubble agent under the same compressing condition; The energy absorption efficiency of foam aluminum could be as high as 90%; it is also found, from the energy absorption figure of foam aluminum, that pure aluminum matrix foam had goodish energy absorption capability and the maximal allowable stress as energy absorption material.