The influence of the concentration of aluminum (Al) and aluminum/nickel (Al/Ni) hybrid fillers on the mechanical and electrical properties of the prepared Al/epoxy and Al/Ni/epoxy composites were studied. The results showed that sample containing 20 wt% Al has the highest compressive strength value whereas the maximum conductivity was observed at 30 wt% Al. By replacing Al by different ratios of Ni in Al/epoxy composites the samples showed a little decrease in conductivity and tensile strength values but an increase in the hardness. The composites were also studied by positron annihilation lifetime spectroscopy. The ortho-positronium lifetime (τ3) results showed that 30 wt% Al and 40/10 wt% Al/Ni are the critical concentrations for Al/epoxy and Al/Ni/epoxy composites respectively. The correlation between positron annihilation lifetime parameters, electrical and mechanical properties was also discussed. A negative correlation was obtained between nanoscale free-volume parameters and mechanical properties for both Al/epoxy and Al/Ni/epoxy composites.
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