Research On Foaming Stability Of The Aluminum Foam Prepared By Extrusion Powder

Aluminum foam is a new kind of porous material compounded by aluminum,aluminum alloy or aluminum matrix composites. During foaming process, a great numberof bubbles formed in interior of the precursor. These bubbles distributed evenly in thematrix, contributed to a porous structure. Thus, aluminum foam obtains both thecharacteristic of continuous phase aluminum, and the characteristic of pores. So aluminumfoam has become one of the most important issues of the highly advanced technology inmaterials science.PCM method is used to produce aluminum foam in this paper. Pure aluminum powderis used as the raw material, titanium hydride powder as foaming agent, and with anaddition of1%pure Mg powder to improve the wet ability of aluminum and oxide.Extrusion is used as the powder forming method. Major factors that influence foamingprocess are studied such as the quantity of foaming agent, the size of the powder, the timeof the foaming processing, the method influence the density, porosity and porous structureof aluminum foam.The results show that: high quality aluminum foams with low density, thin skin, highporous rate, fully developed pore structure and optical-quality homogeneous can beobtained under such conditions: foaming temperature is750℃, the addition of foamingagent is0.4%and the foaming time is about210seconds. Pre-pressing the mix powders,and then heating up to400℃to extrude can effectively eliminate the affection of hydrogenin foaming process. There are two main periods of foaming process: First of all, thenucleation stage. It is the initial stage, the precursor is at a semi-solid state, a lot of tinyround bubbles are formed in this period. And the next step, the evolution stage of bubbles.After the formation of single bubbles, the foaming agent keeps resolving and releasinghydrogen. The bubbles keeps expanding, combining, and form a porous structure withpolygon pores.