Study On Preparation Of Foamed Magnesinum Using Two-stage Process

Foamed magnesium is a composite material consisting of metallic matrix and gas bubbles. Compared to the entity metal, foamed magnesium has low density, large surface area. It also includes many good properties, such as sound absorption, sound insulation, electromagnetism shield, energy absorption, cushioning, heat preservation, filtration and dust catching, etc. So it is widely used in many trades, such as machine, metallurgy, architecture, transport, chemical engineering, telecommunication and so on. In this paper, foamed magnesium is chose as the research object. Evolvement mechanism of pore in molten metal, preparation of foamed magnesium alloy by direct foaming process and two-stage process, effect of foaming process parameters on structure of foamed magnesium and compressive performance of foamed magnesium were investigated.The results show that the driving force of the form growing up in the melt is all from the gas of the continuous vesicant decomposition. During preparation of foamed magnesium using direct foaming process, with the increase of the content of foaming agent MgCO3or viscocity-increasing agent SiC, the density of foamed magnesium decreases. When the content of MgCO3is more than1.5%or the content of SiC is more than15%, the density of foamed magnesium increases a little. As particle size of foaming agent increases, the density of foamed magnesium decreases at first and then increases. When the particle size of foaming agent is250μm, the density of foamed magnesium alloy is the minimum. As the foaming temperature increases, the density of foamed magnesium alloy decreases. With the increase of foaming temperature or particle size of foaming agent, the pore size of foamed magnesium alloy increases. Variation law of density of foamed magnesium is reverse to porosity.Direct foaming process has been improved and two-stage process was investigated, as the addition amount of foaming agent or viscocity-increasing agent increases, porosity of foamed magnesium alloy increases at first and then decreases. When the addition amount of foaming agent is2%or viscocity-increasing agent is0.1%, the porosity of foamed magnesium alloy is the maximum. With addition of2～6%Al, dumping fluidity of melt increases and pore size of foamed magnesium alloy is uniform. With the increase of the addition amount of Al in melt, the porosity of foamed magnesium alloy increases. As the rising of reheating time or reheating temperature, the size of cells increases gradually. When the reheating time exceeds20min or the reheating temperature is beyond610℃, the cells of the foamed magnesium shows an uneven distribution, the merging of bubbles emerges is found in the material. As the rising of reheating temperature or reheating time, the density of foamed magnesium decreases gradually. But when the reheating time exceeds20min, the density of foamed magnesium increases slightly.Through comparing different viscocity-increasing methods and preparation methods, the results show that the viscocity-increasing ability of MgCO3is better than SiC, and two-stage process is more efficient than direct foaming process. The two-stage process is a better way to produce the sample of foamed magnesium with lower density, higher porosity and better distributed holes.Static compression test of foamed magnesium shows that the yield compressive strength decreases from8.1MPa to1.6MPa when porosity increases from61%to81%Besides, with the increase of porosity in the samples, there is a depressed tendency in the elastic modulus, yield stress and intensity of compression. The length of yield stress plane increases with the increase of porosity.