Abstract: The plastic deformation of welding interface material is the essence of friction welding.This paper studied the continuous driving friction welding of LY12 alloy that is often used as aerospace structure material.The plastic deformation on a rod sample of coupled thermal-mechanical analysis model under the electric field based on finite element method was established.Some physical parameter fields about the welding interface material,such as temperature field,strain field and electric field,were calculated.A Yada grain size model was used to predict dynamic recrystallization and grain size growth of the friction welding process.The welding process and the welding quality affected by these physical parameter fields was also analyzed.