Study On Texture,Microstructure And Mechanical Property In Friction Stir-welded AZ31 Magnesium Alloy Assisted By Ultrasonic Vibration And Heat Pipe

Magnesium and its alloy have Hexagonal close-packed structure,and the critical shear stress required for sliding in different sliding planes and directions varies greatly,so it is easy to produce texture in the process of mixing friction welding(FSW),which has a great impact on the weld performance.This project introduces ultrasonic and ultrasonic/heat pipe composite auxiliary into friction stir welding,conduct routine,ultrasonic auxiliary and ultrasonic/heat pipe composite auxiliary friction stir welding for AZ31 magnesium alloy respectively,study the formation process of FSW welding through OM and EBSD,and the influence of different auxiliary conditions on microstructure,and then improve the mechanical properties of welding joints.The main conclusions are as follows:(1)During the evolution of FSW by emergency cold method,it is found that with the influence of thermodynamic coupling,local dynamic recrystalstallization and full dynamic recrystalstallization occurred in the test plate tissue,uniform isoaxial crystals were formed in the weld area,and a strong base texture was formed.(2)Compared with conventional friction stir welding,both ultrasonic auxiliary conditions and ultrasonic and heat pipe auxiliary conditions can promote the dynamic recrystallization of the joint,reduce the low angle grain boundary proportion and grain misorientation of each weld area,make the deformation tissue to substructure and recrystallization and more uniform;the weighted average of Schmid factor in the thermal influence area is high,which is conducive to base sliding and improving mechanical performance.(3)According to the actual production needs,the welding along the welding direction and the rolling direction of the plate are 0° and 90°,under the ultrasonic and ultrasonic/heat pipe composite auxiliary conditions,the organization and structure of the plate show similar changes in the welding process;welding in 90° direction,the organization and structure distribution of the welding area are more uniform and the joint plastic improves.