The cross sections of the original joint, rolled joints, and fractured
fatigue samples were carefully prepared and finally polished using nano
silica (20 nm) polishing solution. The microstructure of 6061-T6 BM,
as-welded SZ, and rolled SZ were observed using EBSD system from Oxford
instrument. The orientation image and grain size were analyzed using
Channel 5 software. The thin film samples with a diameter of 3 mm from
SZs with a thickness of 6 mm and 2 mm were prepared and observed using
TEM (JEM-2100 Plus). The fracture surfaces of the fractured fatigue
samples were observed using SEM (S-3400N). The cross sections of the
fractured fatigue samples were etched using Keller solution and observed
using OM (Zeiss, Observer.Z1m). The lamellar structure in the fractured
SZs with a thickness of 4 mm were observed using EBSD system.
The hardness distribution of the original joint and rolled joints was
measured using micro hardness tester with a load of 100 gf based on the
polished cross-sectional samples. The strength and elongation of the BM
and SZs were measured based on tensile test [22].