Preparation Of Magnesium-based Alloy Foam Material

As a composite material consisting of metallic phase and gas pores, metal foam combines the feature of continuous phase, i.e. metal skeleton, with the characteristic of dispersed phase, i.e. gas pores. It can be applied to many fields, for example, the field of aerospace, transportation, automotive, construction and machinery, metallurgical and chemical industries, as well as electronic communication. As a new kind of metal foam, magnesium foam has attracted researchers more intense interests with the development of metal foam researches.The alloyed ignition-proof method was adopted in this dissertation to prepare ignition-proof magnesium alloy. The interface bonding mechanisms of magnesium matrix composites reinforced by SiC particles or by Al2O3particles were studied. The thermalphysical properties of magnesium alloy or its composites, which were added by SiC particles, were detected. Moreover, the influence of SiC particles on rheological behavior of magnesium alloy melt, and mechanical stirring manners on the distribution of adding agents were also studied. The main conclusions are as follows:(1) Analysis by SEM, EDS and XRD indicates a layer of continuous and dense oxide film was formed on the surface of magnesium alloy melt under high temperature. The oxide film can be divided into two layers. The outer layer is composed of MgO and CaO, and the sublayer is composed of Al2Ca.(2) With temperature declining, the viscosity of Mg alloy melts increases. When the temperature is640℃and540℃, two saltations of viscosity occur. The viscosity of magnesium/SiC composite melt increases as the temperature dropping. However, the viscosity of magnesium/SiC composite decreases greatly compared with magnesium-based alloy melt. In addition, the viscosity of magnesium-based composite melt increases along with the content of SiC particles increasing. (3) With the temperature dropping, the density of magnesium alloy and magnesium/SiC matrix composite increase. After adding SiC particles into magnesium alloy melt, its density has a rising tendency. The surface tension of magnesium alloy melt or its composite increases when the temperature decreases. The surface tensions of magnesium alloy melt increase after SiC particles are added.(4) A layer of SiO2film, which thickness is around1μm, was generated on SiC particle surface after oxidized at high temperature. After treated at high temperature, the silicon carbide particles can be distributed in magnesium alloy melt uniformly, without the phenomena of accumulation and shedding in or from magnesium matrix.(5) Stirring has little influence on rheological behavior of magnesium-based composite melt, whereas has great influence on the preparation of magnesium alloy foam. The inserting depth and diameter of impeller not only have more influences on the dispersion of additives, but also control the melt expansion height. When the impeller diameter is fixed, the density of magnesium foams decreases gradually and its porosity increases as stirring time increasing.