Synergetic effects of cryo-FSP on microstructural, mechanical and corrosion behavior of stir cast AA5083-2 wt% SiC nanocomposite

Abstract

In recent past, a significant research attention has been given to the study of nanosize ceramic particles reinforced aluminium alloy composites due to its excellent mechanical and surface properties compared to unreinforced counterpart. Hence, the major aim of the present study is to investigate the effects of cryocooling friction stir processing (cryo-FSP) on microstructural evolution, and its effects on mechanical properties & corrosion behavior of a stir-cast 2 wt% nanosize SiC (n-SiC) particles reinforced AA5083 nanocomposite in comparison to the room temperature (RT) FSPed and as cast counterparts. The cryo-FSP was performed successfully using optimized process parameters of 1400 rpm and 40 mm/min traverse speed using a specially designed cryo-FSP setup extracting deformation heat efficiently by a flowing mixture of LN2 and methanol (−30 °C). Evolution of a finer equiaxed grain structure (∼2 μm) with a homogeneous distribution of n-SiC particles and precipitate phases is confirmed (through SEM-EBSD and STEM/TEM analysis) in the cryo-FSPed composite compared to RT-FSPed sample (∼4 μm). The cryo-FSPed sample exhibited a superior yield strength (i.e., YS = 230 ± 3 MPa) compared to the RT-FSPed sample (i.e., YS = 197 ± 4 MPa) with a reasonably good ductility for both (i.e., 14 %). The improved YS is attributed mainly to the grain boundary strengthening due to extra grain refinement induced by cryo-FSP and dispersion strengthening via second phase particles. Different strengthening mechanisms' analyses established a good correlation between the theoretical YS and experimentally obtained tensile YS. Fractography analysis corroborated well with the tensile properties of the corresponding samples. Compared to the interdendritic cast structure, both the FSPed samples exhibited a superior corrosion resistance due to an improved surface characteristic developed in the dynamically recrystallized matrix with uniform dispersion of second phase particles. However, due to more grain boundary active phenomenon and higher misorientation angles, a bit higher corrosion rate could be observed in the fine-grained cryo-FSPed sample compared to the RT-FSPed composite.