Stir Casting Routes for Processing Metal Matrix Syntactic Foams: A Scoping Review

Abstract

Metal matrix syntactic foams (MMSFs) are advanced lightweight materials constituted by a metallic matrix and a dispersion of hollow/porous fillers. Physical and mechanical properties can be fitted regarding matrix and filler properties and processing parameters. Their properties make them potential materials for sectors where density is a limiting parameter, such as transport, marine, defense, aerospace, and engineering applications. MMSFs are mainly manufactured by powder metallurgy, infiltration, and stir casting techniques. This study focuses on the current stir casting approaches and on the advances and deficiencies, providing processing parameters and comparative analyses on porosity and mechanical properties. PRISMA approaches were followed to favor traceability and reproducibility of the study. Stir casting techniques are low-cost, industrially scalable approaches, but they exhibit critical limitations: buoyancy of fillers, corrosion of processing equipment, premature solidification of molten metal during mixing, cracking of fillers, heterogeneous distribution, and limited incorporation of fillers. Six different approaches were identified; four focus on limiting buoyancy, cracking, heterogeneous distribution of fillers, and excessive oxidation of sensitive matrix alloys to oxygen. These improvements favor reaching the maximum porosity of 54%, increasing the fillers’ size from a few microns to 4–5 mm, reducing residual porosity by ±4%, synthesizing bimodal MMSFs, and reaching maximum incorporation of 74 vol%.

New Aluminum Syntactic Foam: Synthesis and Mechanical Characterization

“…Positive deviations from theoretical values imply the development of voids or deficiencies of infiltration. The residual porosity in Al-EAn is approximately 5%, which is close to the minimum fraction of voids developed by SCT [ 7 ]. The suitability of the maximum infiltration load of Al-ECn can be demonstrated by the limited residual porosity developed.…”

“…The MIT consists of filling the open porosity between a bed of fillers with molten matrix promoting the infiltration through the mechanical, atmosphere, or inertial forces [ 6 ]. The SCT consists of creating a vortex in the melt and then pouring preheated filler into the vortex to favor homogeneous dispersion [ 7 ]. The P/M consists of mixing fillers and powders of the metallic matrix and then subjecting the mixture to a sintering process at a lower temperature than the matrix melting point.…”

Compressive deformation behavior of closed-cell aluminium syntactic foam

“…The detailed fabrication process was followed according to the previously published work. [12] Figure 1Schematic diagram of stir casting furnace [13]…”

Manufacturing Techniques for Mg-Based Metal Matrix Composite with Different Reinforcements

“…Apart from these factors, tool geometry is also critical. It alters the local microstructure of monolithic specimens to create particular and desirable qualities that are advantageous to the material's performance or requirements [47][48][49][50][51][52][53]. The length, diameter, and shape of the pin, as well as the diameter and shape of the shoulder, have a significant impact on the eventual outcome.…”