Study On The Preparation And Performance Of Foamed Aluminum

Aluminum foam is a composite composed of aluminum and gas.It has many excellent properties,such as small density,good heat resistance and rigidity,and has good impact and shock absorbability,sound absorption and electromagnetic shielding.Aluminum foam is also a reusable environment-friendly material,which has a broad application prospect in architectural decoration,road traffic,mechanical manufacturing and other fields.At present,high manufacturing cost has become a major constraint for the large-scale application and mass production of aluminum foam.In this paper,aluminum foam was prepared from industrial pure aluminum by melt foaming method.Preliminary experiments,TiH₂ was used as foaming agent to prepare aluminum foam.The results showed that the quality of aluminum foam could be significantly improved by adding mg to increase viscosity.However,due to the low initial decomposition temperature of TiH-2 and the fast decomposition rate of TiH₂ in high temperature molten aluminum,the gas easily escapes from the melt,which leads to low foaming efficiency and poor overall quality of aluminum foam.Therefore,CaH₂ and dolomite were selected as new foaming agents to prepare aluminum foam,and their thermal decomposition properties were studied.The decomposition temperature of CaH₂ and dolomite is higher than that of TiH₂,which is more favorable to the preparation of high porosity aluminum foam.Through the control of process parameters,the effects of the amount of foaming agent,the type of tackifying agent,the amount of tackifying agent and the holding time on the porosity,porosity uniformity and average pore size of aluminum foams were investigated.The results show that the amount of foaming agent and holding time are the main factors affecting the pore structure of aluminum foam.At the same time,the effect of porosity on the compressive properties and energy absorption of aluminum foams was analyzed.The porosity of aluminum foams prepared by CaH₂ as foaming agent can reach more than 80%,and the porosity distribution is uniform.Moreover,the difference of internal pore size is small,the average pore diameter is within 2.18mm?3.27mm.When the foaming process parameters are as follows:foaming temperature 680?,holding temperature 600?,holding time 10minutes and CaH₂ content 0.8wt%,the foaming quality and porosity of foamed aluminum are better.The pore size of aluminum foams prepared with dolomite as foaming agent is small,with an average pore size within 0.61mm?0.88mm.Its porosity can also reach more than 80%.When the foaming process parameters are as follows:foaming temperature 700 ?,holding temperature 650?,holding time l00min and dolomite content 1.5wt%,the foaming quality of aluminum foam is better and the pore distribution is uniform.Both magnesium powder and calcium silicate powder can play a good role in viscosity enhancement.Mg and A1 mainly form Al2Mg and MgAl2O4.High melting point SiO2 and composite oxide CaAl2O4 are mainly formed between calcium silicate powder and high temperature aluminum melt.When CaH₂ is used as a foaming agent,the porosity,pore size and pore uniformity of aluminum foam are more suitable when the amount of Mg is 1.5wt%or the addition of silicon calcium powder is 1.5wt%.When dolomite is used as a foaming agent,the quality of aluminum foam is better when the amount of Mg is 1.5 wt%or the addition of silica calcium powder is 2wt%.When aluminum foam is compressed,there are three main stages:elastic stage,yield stage and densification stage.The aluminum foam prepared with CaH₂ as foaming agent shows a unique sawtooth during the yield stage.When the porosity of aluminum foam prepared with dolomite as foaming agent is low,the compression curve is smooth.When the porosity is high,the yield stage also presents sawtooth change.With the increase of porosity,the compressive yield strength decreases,but the stress plateau increases.In addition,the porosity has a great influence on the energy absorption of the sample.Lower porosity or higher porosity will reduce the energy absorption ability of the sample.