Analysis Of Periodic Flow Behavior Of The Severe Plastic Deformation System For FSW

Friction stir welding(FSW)technology,as an efficient solid-phase bonding technology,has unique advantages in meeting the requirements of high reliability,long life and low cost of high specific non-ferrous metals in aerospace.However,the viscoplastic behavior and migration flow of weld metal determine the microstructure and ultimate mechanical properties of FSW joints.Therefore,this paper reveals the Flow characteristics of the severe plastic deformation system in FSW processing by marking material tracing method,and study the law of migration and flow of the severe plastic deformation system.Based on the periodical behavior of the severe plastic deformation system,the characteristic parameters were analyzed in order to reveal the flow mechanism of FSW.The main research contents and results are as follows:The FSW flow characteristics are characterized by "linear" marking materials.After welding,the marking materials have obvious deformation and migration flow due to the strong rotation and extrusion of the tool.There are two kinds of distribution forms: continuous distribution and discontinuous distribution.The 2D flow visualization model and the 3D flow field model are established by extracting the characteristic contour data of the labeled materials.Based on the two-dimensional flow visualization model,the two-dimensional flow characteristics of the labeling materials are described quantitatively and the effect of the tool on the labeling materials is considered.The marker material embedded in the advancing side usually exists in a discontinuous state after welding.The multi-cycle effect of the tool on the marker material leads to instability and dispersion of the marker material.The labeling materials embedded in the center and the retreating side exist in a continuous state after welding.The labeling materials are affected by less or one cycle of the tool.In the action area of the shoulder,the labeling materials move along the retreating side and the rearward side due to the large area of the labeling materials.In the working area of the pin,the labeling materials are migrated along the backward side and the rear.Three-dimensional flow visualization model was established to characterize the three-dimensional shape of the labeled material.Embedded in the advancing side marking material,the continuous action area of the shoulder is connected with the discontinuous action area of pin,and the non-connected part marking material is in the shape of a "thin strip".The marked material embedded in the weld center has a "S" shape change,which is mainly determined by the axial migration of the marked material,and the setting of the tool tilt angle is more obvious.The marked material embedded in the weld center has a large deformation and presents a continuous distribution,and the marked material is affected by the stirring needle for one cycle.After welding,the whole marker material moves backward along the tangent direction,but the migration distance is limited,and the marker material is less than or equal to one period under the action of stir needle.Considering that the material embedded in the center of the weld marker is subjected to the action of the pin for one cycle,the analytical equations of flow velocity,strain,strain rate and viscosity are established,it also reveals the variation law of the above-mentioned parameters with the layer height,and elaborates the flow mechanism of thesevere plastic deformation system,and the calculation results are comparable to those in literature.