Study of internal porous structure formation of the powder metallurgically prepared aluminium foam

The internal pore wall structure formation and density play an important role in improving the mechanical and thermal properties of the closed-cell aluminium foams. The present research work aims to investigate the internal structure formation of the aluminium foam prepared by powder metallurgy and the uniformity of the distribution of the pores when the minimum amount of TiH2 is added. The foamable precursor of two different aluminium alloys (Al-1050 and A5083) is produced with a TiH2 gaseous agent of 0.05 wt.%. The parameters analysed include the density, pore wall formations, pore, and metal density distribution inside the structure with the help of X-ray tomography. Furthermore, the image-processing technique has been adopted to produce the 3D surrogate model of the foam for visual inspection and analysis. The obtained results show the importance of the amount of TiH2 addition and of the foaming furnace temperature in deciding the internal porous structure formation. Further, the pore morphology of lower porosity foams (in the range of 30-40 % porosity) of the two alloys produced at 690 °C furnace temperature is investigated with the help of developed surrogate models. The presence of micropores and uniformity of the distribution of pores found brings the idea of choosing the optimized structure of foam for thermal energy storage systems associated with PCM.

Investigation of the Relationship between Morphology and Thermal Conductivity of Powder Metallurgically Prepared Aluminium Foams

Among different promising solutions, coupling closed-cell aluminium foam composite panels prepared by a powder metallurgical method with pore walls interconnected by microcracks, with low thermal conductivity phase change materials (PCMs), is one of the effective ways of increasing thermal conductivity for better performance of thermal storage systems in buildings. The internal structure of the foam formation, related to the porosity which decides the heat transfer rate, plays a significant role in the thermal energy storage performance. The dependence of the heat transfer characteristics on the internal foam structure is studied numerically in this work. The foamable precursor of 99.7% pure aluminium powder mixed with 0.15 wt.% of foaming agent, TiH2 powder, was prepared by compacting, and extruded to a volume of 20 × 40 × 5 mm. Two aluminium foam samples of 40 × 40 × 5 mm were examined with apparent densities of 0.7415 g/cm3 and 1.62375 g/cm3. The internal porous structure of the aluminium foam samples was modelled using X-ray tomography slices through image processing techniques for finite element analysis. The obtained numerical results for the heat transfer rate and effective thermal conductivity of the developed surrogate models revealed the influence of porosity, struts, and the presence of pore walls in determining the heat flow in the internal structure of the foam. Additionally, it was found that the pore size and its distribution determine the uniform heat flow rate in the entire foamed structure. The numerical data were then validated against the analytical predictions of thermal conductivity based on various correlations. It has been found that the simplified models of Bruggemann and Russell and the parallel–series model can predict the excellent effective thermal conductivity results of the foam throughout the porosity range. The optimal internal foam structure was studied to explore the possibilities of using aluminium foam for PCM-based thermal storage applications.

Research into the Strength of an Open Wagon with Double Sidewalls Filled with Aluminium Foam

The research is concerned with the use of double walls filled with aluminium foam for an open wagon in order to decrease the dynamic stresses during the operational modes. The research presents the strength calculation for the bearing structure of an open wagon with consideration of the engineering solutions proposed. It was found that the maximum equivalent stresses appeared in the bottom section of the centre sill behind the back support; they amounted to about 315 MPa and did not exceed the allowable values. The maximum displacements were detected in the middle section of the centre sill and amounted to 9.6 mm. The maximum deformations were 1.17 × 10−2. The research also presents the strength calculation for a weld joint in the maximum loaded zones of the bearing structure of an open wagon and gives the results of a modal analysis of the bearing structure of the improved open wagon. It was found that the critical oscillation frequencies did not exceed the allowable values. The results of the research may be useful for those who are concerned about designing innovative rolling stock units and improving the operational efficiency of railway transport.