Abstract
Magnesium composite foams with 10 vol. % of hollow ceramic microspheres (CMs) were prepared by modified melt foaming method. Specimens with homogeneous pore structures were subjected to various heating temperature (150, 250, 320, 400, and 500 °C, respectively) and enduring times (1, 2, 4, 6, and 24 h, respectively). Evolution of microstructure and mechanical properties of the samples, before and after the heating processes were examined by applying X-ray diffraction technique (XRD), differential scanning calorimetry (DSC), scanning electron microscopy (SEM), and quasi-static uniaxial compression test. The results showed that as heating temperature and enduring time increasing, β-Mg17Al12 phases gradually dissolved, resulting in a solid-solution strengthening effect. Meanwhile, internal stress relaxation in the matrix leads to the decrease of yield strength and micro hardness of the specimens. When compared with the unheated foams, the treated specimens possessed lower micro-hardness, yield strength, and energy absorption capacity due to the dissolution of β-Mg17Al12 phases and the release of internal stress. However, higher strain hardening exponents for almost all of the treated composite foams were observed and the reasons were discussed. It is proposed that more factors should be taken into account when using heated composite foams in practical applications.
Highlights
In the last few decades, metal matrix syntactic foams (MMSF) with inherent properties of low density, high specific strength, and unique energy absorption capacity have received great attention [1,2,3]
/σ0IS = exp −( At)m where is the internal stress of the as-received Mg composite foams, is the internal stress of the samples heated at the temperature of T for time t, and m is a constant relating to internal stress relaxation mechanism
A is a function depending on the material and heating temperature that is based on Equation (5): IS is the internal stress of where σ0IS is the internal stress of the as-received Mg composite foams, σT,t the samples heated at the temperature of T for time t, and m is a constant relating to internal stress relaxation mechanism
Summary
In the last few decades, metal matrix syntactic foams (MMSF) with inherent properties of low density, high specific strength, and unique energy absorption capacity have received great attention [1,2,3]. Up to date, most of the investigations focused on aluminum or aluminum alloy matrices [6,7,8], only a few studies are available on Mg matrix syntactic foams, e.g., ZC63 magnesium-microballoon composite foams were fabricated by melt stir technique and the processing parameters on the distribution of fly ash microballoons were investigated. Metals 2018, 8, 434 contents of fly ash microballoons were studied [8]. The interaction behavior between AE44 magnesium alloy and SiC-Al2 O3 -SiO2 ceramic foam was studied, and it was revealed that SiO2 was predominantly reduced by Mg during the contact of magnesium-rich melt with the ceramics
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