In order to improve the operation life of welding tool in friction stir welding (FSW) of titanium alloy

the coating was added to the surface of the welding tool

and the effects of surface coating on the operation life of welding tool was studied. FSW of TC4 titanium alloy was conducted by using uncoated and AlCrN coated welding tool. The wear of the welding tool was characterized by 3D imaging instruments

and the microstructure and composition of the joint are analyzed using scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). The influence of AlCrN coating on the service life of the welding tool was studied. The results are as follow: Compared to the uncoated welding tool

the effective welding distance of AlCrN coated welding tool has increased from 600 mm to 800 mm

and after welding in the length of 800 mm

a well formed welding joint with a tensile strength of 95.32% of the base material can still be obtained. In addition

the wear rates of the pin and shaft shoulder of AlCrN coated welding tool are reduced by 50.41% and 22.41%

respectively. AlCrN coating can effectively improve the service life of the welding tool. Comparative analysis of the wear of the welding tool reveals that the wear of the uncoated welding tool includes abrasive wear

bonding wear

and oxidation wear. The wear process mainly includes three stages: initial wear stage

severe wear stage

and stable wear stage. Comparatively

the wear process of the coated welding tool consists of two stages:“ breaking” and“ tearing”.