Study On The Corrosion Behaviors Of Friction Stir Welded Joints Of Al Alloys

Friction stir welding (FSW) is of significant interest to several manufacturing industries, including aerospace, automotive, railway and marine. Whilst many studies have been carried out to investigate the effect of FSW on the microstructure , mechanical properties and fatigue performance of aluminum alloys joints , the corrosion behaviors has received much less consideration.In the scope of this thesis, the anticorrosive performance of friction stir welded aerospace aluminium alloys butt joints, LC4-T4, 7075-T6, LY12-T4 and LD10-T6, have been researched. The performance of corrosion of FSW joints was studied in different corrosive environment for the subsequent friction stir welding process design, welding joints defect analysis to provide reference.In this paper, the corrosion behaviors of FSW butt joints, have been investigated using immersion test in NaCl solution, intergranular corrosion immersion test (ASTM G110) and accelerated test (ASTM G34 EXCO). In addition, metallurgical structure and micro-hardness have been used to analyze the effects of microstructure of different zone and defects on corrosion behaviors.FSW can make a sound joint without any distortion and the microstructure of the welded joint is divided into four zones: weld nugget zone, thermo-mechanically affected zone, heat-affected zone and base material. The shapes of micro-hardness distribution of FSW joints are approximately W and V (LD10). Immersion test in NaCl solution showed that the thermo-mechanically affected zone of FSW is the most vulnerable area. Intergranular corrosion immersion test revealed that the"flash"plays an important role in the corrosion process. Accelerated test also indicated that the thermo-mechanically affected zone is most susceptible to corrosion. Moreover, the accelerated test proved that the defects in friction stir welded joint often referred to as"Kissing Bond"have the lethality danger to the corrosion property. The anticorrosive performance of FSW joints of LY12 and LD10 is better than LC4 and 7075.