Effect of Extrusion Processing on Mechanical Properties of Aluminum/Graphene Nanoplatelet Composites

Abstract In this work the effect of different extrusion parameters on the mechanical properties of aluminum/graphene nanoplatelet (GNP) composites was studied. Composites with GNP-contents between 0.1 and 2.5% were prepared powder metallurgical route. Compacted disks were extruded in direct extrusion. Three different extrusion ratios and two different die angles were studied. Furthermore, exemplarily indirect extrusion processing was carried out to compare the effect of the different material flow patterns in direct and indirect extrusion methods on the resulting composite properties. Characterization of mechanical properties revealed a limited impact of the graphene addition. Applying the direct extrusion method microhardness was increased by up to 15%, TYS by up to 15% also and UTS up to 8%. In compression testing CYS was improved by up to 21% by the addition of 1.5% GNPs. No significant differences of TYS and CYS were found. Application of a conic extrusion die with a die angle of 2 $$\alpha$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>α</mml:mi> </mml:math> =90° instead of a flat face die revealed a better surface quality of extruded rods. But regarding mechanical properties, flat face die led to 6% higher hardness, higher tensile yield strength of 13% as well as of 8% higher ultimate tensile strength. Increasing the extrusion ratio led to higher values of microhardness of 16% for pure aluminum and 10% for a GNP content of 0.5%. Additionally, increasing fracture strains were found as extrusion ratio was increased. Processing via indirect extrusion had no significant effect on the resulting mechanical properties compared to direct extrusion mode.