Study Of Small-aperture Aluminum Foam Preparation Technique

Aluminium foam is a new material composited of gas and A-alloy,integrating high specific strength and functionality.Because of its multifunctionality,aluminum foam has much potential applicatious in many fields such as automotive,aviation and building industry.Melt foaming is the main processing for fabricating aluminium foam.However, There are such issues about the process to be solved as:the uniform of foaming agent dispersion,too big pore diameter,and the matching of decomposition of foaming agent and foaming processing.To solve the problems above simultaneously,based on the melt foaming processing, some improvement are adopted as followings:(1)Using the oxidized foaming agent to improve the matching of decomposition of foaming agent and foaming processing;(2)Stirring the melt when foaming agent are decomposing;(3)Adding Mg in the melt to increase surface tension of the melt;(4)Adding nucleation agent in the melt to increase heterogeneous nucleation.Aluminium foam with fine pore diamete was made sucessfully in this paper.The averge cell diameter of aluminum foams by this process is about one millimeter,and the cell structure are distributing uniform.The optimal processing parameters was:melting and preservation temperature of alloy 625℃;content of Ca 2.5%;content of Mg 0.5%; content of nucleation agent 0.5%;stiring time 12 min;content of foaming agent 1%; foaming agent being treated on 400℃6h and 475℃1h;foaming time 50s;stirring speed 1500r/min;time of heat insulation 2 min 30s.Decomposition characteristics of foaming agent,the mechanism of Mg and nucleation agent were studied.Oxidizing of foaming agent could delay the starting decomposition time,slower the decomposition rate,and make the pore diameter being smaller with stirring the melt;adding Mg in the melt could increase surface tension of the melt,make the pore being easy to maintain;adding nucleation agent in the melt could increase heterogeneous nucleation,the gas that foaming agent decomposed is invariablenes,so increasing the heterogeneous nucleation could make each pore being smaller.The compressive propertie of aluminium foam(porosity between 68%-75%) indicated the fabricated aluminium foams belong to ductile foam roughly,yield strength is between 6 MPa to 10 MPa,energy absorption capability is between 3 MJ/m~3 to 6 MJ/m~3, therefore the fabricated aluminium foams have the capability of energy absorption.Pore diameter of aluminium foam has effects on the properties of the aluminum foams,with the pore diameter being smaller,yield strength and energy absorption capability will increace strongly.AlSi9 foams with fine pore diameter(the pore diameter is about 1 mm)have been fabricatied successfully,and the mechanics of reducing the pore diameter and the basic compressive data have been discussed in this research.It is meaningful to promote the development of aluminum foams.