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

Alejandro Miguel Sánchez De La Muela,Francisco Javier Elorza,Joana Duarte,Luis Enrique García Cambronero,João Santos Baptista,José Manuel Ruiz-Román

doi:10.3390/pr10030478

Alejandro Miguel Sánchez De La Muela, Francisco Javier Elorza + Show 4 more

Open Access

https://doi.org/10.3390/pr10030478

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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%.

Highlights

The study of foam-like structures is guided by the objective of obtaining lightweight engineered materials with exceptional properties, such as excellent energy-absorbing capabilities, high damping, and increased specific strength [1]
Articles were collected in electronic databases based on specific keywords, and the selection was based on a set of screening/exclusion criteria
From the set of 33 manuscripts included in this study, four aspects of interest have been identified: manufacturing processes and mechanical, tribological, and microstructural properties

Summary

Introduction

The study of foam-like structures is guided by the objective of obtaining lightweight engineered materials with exceptional properties, such as excellent energy-absorbing capabilities, high damping, and increased specific strength [1]. Foams are applied in those materials that require the properties described above and in which low density is a limiting parameter. There are mainly two types of foams (closed-cell or open-cell) that can be produced in diverse materials (polymers, metals, and ceramics). The so-called syntactic foams (SFs) result from these efforts of updating conventional closed-cell foams and a relatively new type of composite materials [3–5]. This family of new materials consists of a continuous matrix embedding a dispersion of porous or hollow filler particles following closely or randomly packed structures [6–8]

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