The Research On Friction Stir Welding Process And Plastic Flow Behavior Of Cu-Zr Based Amorphous Alloy

Amorphous alloys have excellent mechanical,physical and chemical properties,but their small size and simple shape still restrict their application.Welding amorphous alloy by taking advantage of their superplastic flow capacity during super-cooled liquid region expands the range of engineering application.Friction stir welding is a complex thermal-mechanical coupling process.It helps to gain the influence of process parameters on joint structure,understand the formation mechanism of welding seam,and provide guidance for obtaining high-quality welding seam,by studying the changes of microstructure and mechanical properties before and after welding,as well as the plastic flow behavior during welding.In this article,Cu₃₆Zr₄₈Ag₈Al₈ amorphous alloy was selected for friction stir welding to explore the influence of process parameters on the surface morphology,microstructure and micro-hardness.In addition,the plastic flow behavior in the welding of amorphous alloy was analyzed by means of copper powder tracer,and a plastic flow model was proposed.The welding test reveals that friction stir welding of Cu₃₆Zr₄₈Ag₈Al₈ amorphous alloy requires additional thermal source around 150?.When rotation speed is 400rpm,welding speed is 15 mm/min,and a shoulder drilling depth is 0.1 mm,great weld morphology can be obtained.The secondary phase is induced by high plastic deformation in the amorphous alloy.There are a lot of void defects,but no amorphous alloy is oxidized during the welding.The shearing action and the heat action during the welding will affect the size and distribution of the secondary phase.Further,the morphology of the secondary phase and the thermal action can affect the micro-hardness.Plastic flow test illustrates that most of the plasticized amorphous alloy in front of the tool pin in advancing side travels to the retrograde side subjected to the shearing action of the tool pin during friction stir welding,and a small part of it flows back along the edge due to the extrusion with partly depositing behind the tool pin.In the retrograde side,the plasticized amorphous alloy in front of the tool pin will travel directly to the rear of the tool pin and deposit,with a part of it entering the advancing side.Due to the accumulation of plasticized amorphous alloy in both the advancing side and the retrograde side in front of the tool pin,the migration movement in the direction of thickness will occur under the action of axial pressure while moving in the horizontal direction.Part of the plasticized amorphous alloy close to the shoulder of will move away from welding seam,and the tendency of movement on the retrograde side is stronger.The distribution analysis of copper powder depicts that the distribution of copper powder is diverse in different cross sections after welding.Along the welding direction,copper powder first appears in the center of the welding seam,gradually expands toward the edge until it covers the entire welding seam,and then shrinks toward the edge again.The analysis of the void defect displays that the shearing action of the tool pin affects the morphology of the void defect.Due to the shearing action decreases with the increment of depth,the void size increases gradually and the number of void decreases.