Micro Structural Characteristics of Friction Stir Welded AA6061-T6 Joints Reinforced with Different Nano Particulate
An attempt was made to improve the mechanical properties of AA6061-T6 alloy welded joint by refining the microstructure and confining the coarsening of strengthening precipitates at the weld and the heat-affected zone (HAZ). Friction stir welding process (FSWP) was used to fabricate AA6061-T6 alloy composite joints with and four different nano reinforcement particles (RP) of Silicon Carbide(SiC), Boron Carbide(B4C), Titanium boride (TiB2) and Aluminum Oxide(Al2O3) at varying volume fractions (5%, 10%, and 15 .%) All of the Friction stir welded (FSW) joints with different RP were designed under the same operating conditions(900r.p.m, 50mm/m, and zero tilt angle). The pinning effect caused by the added nanoparticles prevents grain growth, which occurs frequently after recrystallization stage of FSW process, and it also restrains grain coarsening by obstructing grain boundary path motion. The microstructures of all FSW composite joints revealed a remarkably refined grain at HAZ and nugget zone(NZ). The finding of mechanical testing's revealed that among all four RP, B4C particles had alittle more influence on hardness values but the SiC particles made more influence on Strength of the FSW composite joints. The hardness of composite joints increased as volume friction increased. The tensile strength trend in composite joints was the opposite of the hardness trend. Due to a non-homogeneous distributed nano-particatu and poor interaction, FSW created voids and crack initiation at the RP and BM interface in 15%volume fraction composite joints. As a result, these joints fractured prematurely during the stress test. All of the broken surfaces were examined using a SEM. Mixed ductile and brittle fractures were revealed in composite joints with a volume fraction between 5% and 10%.