High efficiency dispersal and strengthening of graphene reinforced aluminum alloy composites fabricated by powder metallurgy combined with friction stir processing

1 wt.% graphene nanoplatelets reinforced 2009Al (GNP/2009Al) composites were fabricated by a combination of powder metallurgy and subsequent multi-pass friction stir processing (FSP). Microstructural examinations showed that the GNP distribution was significantly improved as the number of FSP passes increased, with a uniform dispersion of GNPs achieved after 2 FSP passes. The layered structures of GNPs were well retained and most of the GNP-Al interfaces were clean and well bonded in FSP composites. Tensile tests showed that the strengths and the elongation of the composites increased initially and then decreased, as the number of FSP passes increased from 1 to 4 passes. In particular, the 2-pass FSP composite exhibited a maximum ultimate tensile strength and yield strength of 514 MPa and 398MPa, an increase of 23.3% and 30.5%, respectively, compared with 2009Al alloy. Moreover, a sound elongation of 10% was obtained for the 2-pass FSP composite. A strength calculation based on load transfer indicated that the high efficiency strengthening of the composite could be attributed to the large specific surface area of uniformly dispersed GNPs. (C) 2018 Elsevier Ltd. All rights reserved.