Study On Recycling Of Scrapped Aluminum Foam And Heat Conduction Simulation In Aluminum Foam

Owing to its structure and function properties, aluminum foam has a wide range of applications in automotive, construction and aerospace field. When their service devices upgrade, aluminum foams scrap inevitably. The aluminum foam has incomparable advantages over other traditional insulation material for the thermal insulation and heat preservation. However, the available aluminum foam effective thermal conductivity theoretical model, due to its limitations, is difficult to provide the relationship of thermal conductivity process and the complex structure of aluminum foam. Therefore, study on the recycling of scrapped aluminum foam and the thermal conductivity process of aluminum foam has important application value and theoretical significance for the sustainable development of aluminum foam industry.The recycling remelting process of scrapped aluminum foam and the re-foamed condition of secondary aluminum were investigated.The control volume method, randomly generated program of aluminum foam and computer simulation were adopted to review the thermal conductivity process and influence factors.The conclusions were as follows:(1) The results of the scrapped aluminum foam remelting process show that: adding flux at the top of scrapped aluminum foam in remelting process can prevent the oxidation of aluminum at high temperature, effectively separate the liquid aluminum and the oxides, eliminate the foam float and increase the recovery rate ultimately. The main influence factors on recovery rate are flux formula, flux dosage and melting temperature. Flux formula and their relative mass(fluoride components is less than 20%) have a certain impact on the recovery rate; Recovery rate firstly increased and then decreased with flux addition increase; Effect of temperature on the recovery rate is indistinctive. The best result can be reached when elected NaCl-KCl system(fluoride components is less than 20%), flux addition 20%-30%, melting temperature 680℃-700℃, straight recovery rate is up to 80%.(2) Some drawbacks such as pores, cracks and oxide inclusions exist in recycled aluminum, which is not suitable for metal parts direct preparation. It is an economical way to prepare aluminum foam using recycled aluminum. However, recycled aluminum contains tackily agent and calcium remnants of foaming agent, which make the viscosity of aluminum melt too high to preparation of aluminum foam. Adding some original aluminum into recycled aluminum can "decrease" the viscosity of aluminum melt. The proportion of original aluminum 5%-10% can ensure suitable viscosity of aluminum melt to prepare aluminum foam.(3) Then novel foaming agent(NFA) was added into aluminum melt to prepare aluminum foam after obtaining suitable viscosity of aluminum melt. Aluminum foam samples with porosity of 60%-80%, average pore diameter 1-4mm can be produced when the foaming temperature of 720℃, the foaming agent addition of 1.6%-2.2%, stirring time of 3-5.0min, stirring rate of 1500-2000rpm and holding time of 8.0-10min.(4) Control volume method was used to derive the discrete equation of aluminum foam heat conduction process, and the numerical algorithm program of the effective thermal conductivity was compiled. Through comparison of measured and calculated values, it can be found that when porosity is above 83% the calculated values match the measured values well, while the calculated values are higher than the measured values when porosity is below 83%.Those low porosity aluminum foam contain a lot of micro-porous. Considering the effect of those micro-porous on the effective thermal conductivity, a nested algorithm was introduced to modify the numerical algorithm program. Finally the numerical solution was close to the measured values, which proved that the numerical calculation method is reliable. Those approach not only consider the objective composition of aluminum foam, but also in accord with the actual thermal conductivity process, which can show that the calculation methods and procedures are suitable for analyzing the thermal conductivity process of random distribution aluminum foam medium.(5) Effective thermal conductivity increase with the proportion of the matrix increase(porosity reduce); For the porous structure with same porosity, different pore distribution result in different effective thermal conductivity, which indicate that the pore distribution has much impact on thermal conductivity of aluminum foam. Through analyzing the temperature field, it can be found that the temperature has mutations in the junction of the matrix and the pore and so that the temperature gradient in the pores became larger. The distribution temperature in the aluminum foam is non-uniform, which is closely related with the pore size and distribution.(6) In the case of the same porosity, pore structure and distribution are dominating factors of thermal conductivity of aluminum foam. The pores which extend or distribute along the direction perpendicular to heat flow strengthen obstructive capability for heat flow. When pores connect along the direction perpendicular to heat flow, a "wall of high thermal resistance" appears to decline the thermal conductivity rapidly. This shows that only porosity can not completely determine effective thermal conductivity of aluminum foam, so the previous studies (forecasting equation includes only the porosity) have significant limitations and uncertainties.