The compressive behaviour of eight different metal matrix syntactic foams (MMSFs) are investigated and presented. The results showed that the engineering factors as chemical compositions of the matrix material, the size of the microballoons, the previously applied heat treatment and the temperature of the compression tests have significant effects on the compressive properties. The smaller microballoons with thinner wall ensured higher compressive strength due to their more flawless microstructure and better mechanical stability. According to the heat treatments, the T6 treatments were less effective than expected; the parameters of the treatment should be further optimized. The elevated temperature tests revealed ~30% drop in the compressive strength. However, the strength remained high enough for structural applications; therefore MMSFs are good choices for light structural parts working at elevated or room temperature. The chemical composition -microballoon type -heat treatment combinations give good potential for tailoring the compressive characteristics of MMSFs.

This paper presents the possibility of syntactic foam production by pressure infiltration technology. Syntactic foams have low density and relatively high strength. Therefore they can be the material of many important parts in automotive technology or in aviation. The parameters of infiltration were studied and physical and mechanical investigations were performed. Microscopic investigations showed almost perfect infiltration at the applied infiltration pressure. The densities of the foams were significantly decreased. Low density ensures good specific properties and economical energy consuming in the case of moving the parts. Syntactic foams showed a plateau region in their upsetting diagrams and absorbed a high energy during upsetting. The effect of aspect ratio was also investigated. Specimens with higher aspect ratios showed lower peak stress, lower plateau level and higher modulus of elasticity.Keywords metal matrix composite · pressure infiltration · metallic foam · syntactic foam · ceramic microballoon · hollow sphere.

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HighlightsLow pressure infiltration is suitable to produce MMSFs with hollow iron spheres.The MMSFs showed plastic yielding and long, slowly ascending plateau region.The matrix and the heat treatment strongly influence the properties of the MMSFs.The full-scale FEM model gives excellent agreement compared to the measured values. Highlights (for review) *Manuscript Click here to view linked References AbstractAluminium alloy syntactic foams reinforced with iron hollow spheres were produced by low pressure, liquid phase inert gas infiltration technique. Four Al alloys (Al99.5, AlSi12, AlMgSi1 and AlCu5) and Globomet grade iron hollow spheres were used as matrix and reinforcing material, respectively. The produced composite blocks were characterised according to the ruling standard for compression of cellular materials in order to ensure full comparability. The compressive test results showed plastic yielding and a long, slowly ascending plateau region that ensures large energy absorption capability. The proper selection of the matrix material and the applied heat treatment allows for a wide range of tailoring of the mechanical properties. For design purposes, the full-scale finite element method (FEM) model of the investigated foams was created and tested on Al99.5 matrix foams. The FEM results showed very good agreement with the measured values (typically within 5% in the characteristic properties and within 10% for the whole compression curve).

Hybrid metal matrix syntactic foams (hybrid MMSFs) are particle reinforced composites in which the reinforcement is the combination of more than one grade of hollow spheres. The difference between the spheres can be in their chemical composition, dimension, physical properties etc. In this study AlSi12 matrix hybrid MMSFs with monomodal Globocer (Al2O3 and SiO2 based ceramic) and Globomet (pure Fe) reinforcements were produced by pressure infiltration. The investigation parameters were the ratio of the hollow sphere grades and the aspect ratio of the specimens. Microstructural investigations showed almost perfect infiltration and favourable interface layer, while quasi-static compression tests showed that the composition of the reinforcement and the aspect ratio of the specimens have determinative effect on the characteristic properties (compressive and flow strength, fracture strain, stiffness and absorbed energy). This nature of the MMSFs ensures the possibility to tailor their properties in order to optimise them for a given application.