Effect of brass interlayer on microstructure,mechanical and corrosion behaviour of friction stir welded AA6061-T6 alloy

Abstract

In this study, friction stir welding (FSW) was performed on AA6061-T6 with and without brass interlayer. The FSW with interlayer was performed for various tool rotational speeds (600–1000 r/min) and at constant travel speed (25 mm/min). The defect-free joint with uniform distribution of brass particles in the stir zone (SZ) and formation of the uniform composite structure was observed at an intermediate optimized tool rotational speed of 800 r/min due to the proper material flow. A strong metallurgical bond between brass particles with aluminium alloy resulted in the formation of Al₂Cu and Al₄Cu₉ strengthening intermetallic compounds (IMCs). The average grain size obtained for the weld with interlayer is smaller than weld without interlayer. The presence of the interlayer enhanced the hardness and the tensile strength compared to the weld without interlayer. This improvement in mechanical properties with interlayer is attributed to the formation and uniform distribution of strengthening IMCs. The corrosion analysis was carried out in 3.5% NaCl solution using immersion test and electrochemical polarization test. The weld with interlayer showed enhanced corrosion resistance than the weld without interlayer which is attributed to the formation of major Al₂Cu IMC which has less activation energy for the corrosion process.