Study On Foaming Mechanism Of Powder Metallurgy-Foaming Process

Foam aluminum material has special sound-absorbing properties,sound insulation performance,energy absorption,electromagnetic shielding performance,heat transfer performance and damping performance.So if is widely used in vehicle manufacturing,construction,aerospace,military and other fields.Powder metallurgy foam method has the advantage of near final shape.It has unparalleled advantages in the production of aluminum foam profile.However,foam aluminum produced by this method has poor cell uniformity,cell size is not controllable,the roundness and the wall of the cell are poor.There are many studies on properties and applications of aluminum foam at home and abroad,but little research has been done on the foaming mechanism of aluminum foams.This experiment is funded by the National Natural Science Foundation project "Study on foaming mechanism of powder compact melting process based on SR-CT".Using the Beijing synchrotron radiation 4W1A imaging station equipment group to observe and record the foaming process of aluminum foam samples,a series of foam images were obtained.By analyzing and contrasting these foaming images,the foaming mechanism of powder metallurgy foaming method is explored,which provides the theoretical basis for practical production.The experiment has the following conclusions:(1)There are two mechanisms when foaming the foam samples containing copper coated carbon fibers.Type ?:the hydrogen generated by the decomposition of the blowing agent is foamed on the basis of TiH2 particles.Type ?:the hydrogen generated by the blowing agent is foamed on the basis of copper coated carbon fibers.(2)In the cell nucleation stage,copper coated carbon fibers can effectively reduce the nucleation temperature of aluminum foam,provide the basis for the formation of cells and make basis distributed more uniformly.Effectively mitigating the concentration of stress caused by hydrogen accumulation and reducing the possibility of defects such as cracks,so that make the nucleation stage more stable.In the cell growth stage,copper coated carbon fibers can make cells growth more stable,more evenly distributed and reducing the possibility of serious cells uneven distribution.In the cell consolidation phase,it can make can effectively hinder cell movement and the merger process is relatively slow and stable.(3)There are two cases of cell merger,one is the two cells merged just after the contact,the other is the two cell contact for a period of time before merging.Insufficient cell consolidation can create holes in the cell walls between the two cells,even larger through-hole can be created.In the cooling state,the two contact cells will appear the phenomenon of separation.(4)Cell rupture will make the cell size smaller,the rupture of the surface cells will make the oxide surface of aluminum foam appear cracks that can't heal.(5)Foam collapse occurs when the foam solidifies,failure to replenish the liquid metal during the collapsing process will cause defects such as irregular cells or cracks in the foam.(6)In the cell nucleation stage,Al2O3 particles will hinder the growth of nucleation bubbles,and even make the nucleating bubbles unable to grow up.The presence of Al2O3 particles causes serious loss of hydrogen gas.In the cell growth and merger stage,Al2O3 particles increase the temperature of cell's growth and merger.It makes the bubble grow and merge rapidly and increases the difficulty of controlling foam structures.In the latter stages of foaming,the Al2O3 particles greatly reduce the stability of the cells and fail to obtain a stable foam structures.