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].