Preparation Of Foam Aluminum By Transfer Foaming Method And Pore Structure Control

Aluminum foam is a porous functional material composed of metal phases and pores.Because of its many excellent properties,such as small density,high specific strength,good energy absorption,electromagnetic shielding,sound absorption and sound insulation,it has been widely applied in many fields such as transportation,construction machinery,aerospace and so on.The main methods for preparing aluminum foam are powder metallurgy,percolation casting,investment casting and melt foaming.Because of its simple preparation process and low production cost,the melt foaming method is suitable for the production of large size aluminum foam.Therefore,it has attracted more and more attention in the industrial production.The foamed aluminum obtained directly from the melt in the crucible is a cylinder,which has certain limitations on the preparation of large size plates.The study on the preparation of foam aluminum by transfer foam method and the control of pore structure provide a theoretical basis for the production of large size and high quality aluminum foam.In this paper,industrial pure aluminum is used as the matrix material,metal calcium（Ca）is used as the tackifier,and Ti H₂is used as the foaming agent.The optimum technological parameters were determined by orthogonal test,including the main technological parameters of the foam foaming process,the adding amount of the tackifier,the amount of foaming agent,the holding time and the holding temperature.The effects of the 4 technological parameters on the pore structure of the foam aluminum were analyzed respectively.Under the condition of this experiment,the mixing device of mechanical stirring method was designed and improved,the best foam aluminum sample was obtained,the influence of the thickness of graphite impeller on the pore structure was analyzed,the pore structure of the best foam aluminum sample was analyzed,and the effect of different stirring devices on the pore structure of aluminum foam was analyzed.The experimental results show that:（1）The optimum process parameters are determined by orthogonal test:The addition amount of metal calcium is 1.5%,the addition amount of titanium hydride is 1.5%,the holding temperature is 690℃and the holding time is 5min.（2）When the adding amount of the tackifier is too high,the cavity of foamed aluminum is easy to appear.When the addition of the tackifier is too low,it is easy to appear large aperture,no bubble layer is thicker and collapse,which will cause uneven pore structure of the foam aluminum.When the amount of foaming agent increased,the pore size and porosity of foam aluminum increased.When the speed of stirring foaming agent is too high or the stirring time is too long,the pore size and porosity of foam aluminum will decrease.When the insulation foaming time is too long or the insulation temperature is too high,the pore diameter will increase,and it is easy to have large pores or collapse,resulting in uneven pore structure.（3）Improved the graphite stirring paddle from 20mm to 30mm thick,and obtained the best foam aluminum sample with uniform pore structure,high porosity,no bubble free layer and few defects.The pore structure of the best sample vertical section was characterized by two value analysis of the whole and stratification.The overall pore size of the sample was smaller,and the average pore size of the pore structure from the upper layer to the lower layer gradually decreased and gradually became uniform.（4）The power increasing electric agitator with power of 300W is improved to the mixing device of YCT electromagnetic speed regulating three-phase asynchronous motor with power of 1.1k W.Increasing the power of the agitator can make the melt form a whirlpool and get sufficient stirring.In order to standardize the technological operation conditions,aluminum foam with good pore structure was obtained.