Microstructure And Properties Of Friction Stir Welded Joint Of Al-Mg-Mn-Zr-Er Alloy

Friction stir welding?FSW?,as an advanced welding technology,has incomparable advantages and has been widely used in aluminium alloys.Al-Mg-Mn-Zr-Er alloy has been used in industry as a microalloyed Al-Mg alloy such as 5E83 and 5E06.It is of great significance to explore the microstructures and properties of Al-Mg-Mn-Zr-Er alloy welding joints during friction stir welding for the application and popularization of Al-Mg-Mn-Zr-Er alloy.In this paper,the effects of Er and Zr on the microstructure and properties of friction stir welding joint of Al-Mg-Mn-Zr-Er alloy under different process conditions are investigated and studied.The results are listed as follows:1.The mechanical properties of the friction stir welded joint of Al-Mg-Mn-Zr-Er alloy are highly correlated with the welding process parameters.When the welding process parameters are 800 rpm×100 mm/min,the welded joint can obtain good tensile strength and elongation..When the welding process parameters are 800 rpm×80 mm/min and 600 rpm×80 mm/min,the Al-Mg-Mn-Zr-Er alloy friction stir welded joints have poor elongation.2.Corrosion resistance of welded joints has little correlation with welding process,which is mainly related to different positions of welded joints.In the electrochemical process,the influence zone of corrosion resistance of welded joints is shoulder>base metal>heat affected zone,and the main influencing factor is grain structure state;intergranular corrosion ability is mainly related to beta phase,and the order of intergranular corrosion resistance of welded joints is welding.Nuclear zone>heat affected zone>base material.3.The microstructural transformation sequence of Al-Mg-Mn-Zr-Er friction stir welding is discontinuous dynamic recrystallization,dislocation introduction,dynamic recovery and continuous dynamic recrystallization.Er and Zr play two main roles in the transformation process of Al-Mg-Mn-Zr-Er alloy structure:on the one hand,the retardation of Al₃?Er,Zr?relative to dislocation hinders the recovery and recrystallization process of welded joints;on the other hand,both the precipitation of Al₃?Er,Zr?along dislocation and the recrystallization process consume the intracrystalline energy,so there is a competitive relationship between them.Therefore,the recovery and recrystallization process is also important during the precipitation process.It has an obstructive effect.Er and Zr microalloys have fine grain strengthening and precipitation strengthening effects on welded joints during tension,thus improving the mechanical properties of welded joints.