Microstructure and mechanical properties of Graphite reinforced aluminum matrix composites fabricated by multi-passed friction stir processing (FSP)

Friction Stir Processing (FSP) is known as a solid state process with a significant capacity of fabricating fine grained surface composites from Aluminum metal matrix. In this work, we used Graphite particles (20-50 μm) as reinforcing secondary phase in AL1050 matrix, in order to improve mechanical properties throughout this process. Graphite particles preplaced into machined grooves in the middle of the aluminum1050 sheet and multi-passed FSP applied. The microstructure of the composites examined byusing optical microscopy (OM) and scanning electron microscopy (SEM). It identified that Graphite particles were well dispersed in the Aluminum matrix throughout the multipassed FSP. In addition, the average grain size of the stir zone decreased due to dynamic recrystallization during the high temperature severe plastic deformation. Tensile tests and microhardness measurement showed that, with the increase of graphite particles content, the tensile strength and microhardness of the Graphite/AL1050 composites remarkably increased, on the contrary, the elongation decreased due to brittle nature of the graphite particles. The maximum ultimate tensile strength reached up to 193 MPa and the microhardness enhanced to 74.4 (HV) when 3 Wt.% Graphite were added. In addition, the composite became more and more brittle when the weight percent of the Graphite content increased.

Keywords:

Friction Stir Processing , Surface composite , Aluminum alloys , Graphite particles