Investigating on microstructural and mechanical properties of Al6061/nano–SiC composites fabricated via friction stir processing

Abstract

In this investigation, metal matrix composite was fabricated on the surface of Al6061 plates using means of 50 nm SiC particles via friction stir processing(FSP). X-ray diffraction(XRD), electron backscattering diffraction (EBSD) and transmission electron microscopy(TEM) were employed to detect and analyze the morphology and characteristics of precipitated phase and composite strengthening phase as well as the grain microstructure in samples. The microhardness and tensile properties of the samples were also tested. The results show that the ratio of low angle grain boundaries(LAGBs) decreased from 56% to 39% of the base metal owing to severe plastic deformation and the addition of nano-SiC particles, and that of the high angle grain boundaries (HAGBs) increased from 44% to 61%, which significantly refines the grain structure in the stir zone(SZ). The hardness profile of Al/SiC metal matrix composite sample is an inverted ‘U’ curve, which is different from the case that the hardness distribution of FSPed Al6061 alloy is a typical ‘W’ shape. Grain refinement and SiC dispersion strengthening compensate the defects of hardness reduction and uneven distribution caused by the dissolution in stir zone or coarsening in thermo-mechanically affected zone of Mg2Si precipitates due to the increase of temperature. Microhardness in stir zone increased from 78 HV to 100 ± 5 HV, which was improved up to about 28% comparing with base metal Al6061 alloy.