The production of Al–Cu–Fe metal foam is a complex technological task due to the high melting point of the components and the tendency to form intermetallic compounds. Traditional methods using foaming agents or spatial frameworks have a number of limitations associated with contamination of the material with foaming agent residues or the need to remove the framework after foam formation. An alternative approach is to create foam without using these auxiliary elements, which allows for a cleaner and more homogeneous material.
One promising method is to use the self-organization effect during melt solidification. Under certain conditions, the Al–Cu–Fe alloy may undergo gas phase release during cooling, which leads to the formation of a porous structure. The key factor is to control the cooling rate and alloy composition to create optimal conditions for nucleation and growth of gas bubbles.
This study investigates the spontaneous foam generation in Al68Cu20Fe12 alloy without any foaming additives or supporting structures. The alloy was slowly solidified in a furnace crucible, resulting in the formation of a multicomponent microstructure consisting mainly of λ-Al13Fe4, icosahedral, θ-Al2Cu and ω-Al7Cu2Fe phases.
To achieve porosity above 60% in foams, the cast alloy samples were subjected to different heat treatment regimes. The microstructure, thermal properties, pore structure and porosity values were determined by SEM, DTA, image analysis and Archimedes method.
The maximum macroporosity reaching 65% and the density of 1.5 g/cm3 in the treated sample were recorded at a temperature of 900 °C and a holding time of 360 minutes. Under these conditions, a structure with high porosity was formed, consisting mainly of the λ-Al13Fe4, I-icosahedral and ω-Al7Cu2Fe phases.
The proposed mechanism for the formation of internal porosity is based on the presence of a significant volume of liquid phase formed during the melting of copper-rich phases and as a result of the peritectic reaction. As a result of the interaction between λ-Al13Fe4 and liquid phases, high-density ω-Al7Cu2Fe phases and icosahedral phases were formed. The space remaining after these processes led to the formation of a highly porous structure in this material.
To achieve uniform pore distribution and improve the mechanical properties of the foam, various technological methods are used, such as the addition of alloying elements, ultrasonic action or the use of special forms for solidification. Controlling the microstructure of the foam allows you to vary its density, pore size and distribution, which opens up opportunities to create materials with specified properties for various applications, including thermal insulation, sound absorption and vibration damping.
Author: M. A. Suarez, I. A. Figueroa, G. Gonzalez, G. A. Lara-Rodriguez, O. Novelo-Peralta, I. Alfonso, I. J. Calvo
Institute: Institute for Materials Research, National Autonomous University of Mexico (UNAM), Circuito Exterior S/N, Cd. Universitaria, CP 04510 Mexico City, Federal District, Mexico, Department of Chemistry, Department of Metallurgy, National Autonomous University of Mexico (UNAM), External Address S/N, University Street, P.O. Box 04510, Mexico City, Federal District, Mexico