The Influence Of Tool Configuration And Welding Parameters On The Transfer Behavior Of The Plastic Metal

The friction stir welding of LY12 aluminum alloy plates like sandwich in which the tracing materials of aluminum foil were inserted was conducted by using six kinds of welding tools. After welding, the metallographic samples were cut in three ways, that is, along the plane at the weld centerline, the plane perpendicular to the weld direction and the plane paralleled to top surface of the weld. The influence of welding tools configuration and welding parameters on the transfer behavior of the plastic metal was analyzed according to the distribution of tracing materials. The model for the three-dimensional flow field of the plastic metal was set up, the simulation was carried out by using software FLUENT, the three dimensional velocity and flow line trajectory of plastic metal were analyzed.The results showed that, the tool configuration is an important factor affecting the transfer behavior of the plastic metal. During welding process, the pin with left-hand thread drives the plastic metal around it to move downwards, then the plastic metal accumulates at the tip of the pin to form an extrusion zone and the zone begins to force its peripheral metal to move upwards when it is blocked by the backing plate; after welding, the extrusion zone usually presents onion rings pattern at the cross section of the weld. however, the pin with right-hand thread has different influence on the transfer of the plastic metal, the plastic metal accumulates at the root of the pin to form an extrusion zone which force its peripheral metal to move downwards. Based on the Hydrodynamic theory and experimental observations, the physical model for sucking-extruding of plastic metal is established, the thread of the pin is the main reason for driving plastic metal to flow in the weld thickness direction. When the weld is conducted by using thread pin with large pitch, the phenomenon of suction-extrusion of the plastic metal is very prominent and the areas of the extrusion zone become large, it is easier for the extrusion zone to expand in the weld thickness direction when the weld is conducted with larger diameter of the shoulder.The transfer behavior of the plastic metal in the weld thickness has relationship with the selection of welding parameters. With the increase of the rotating velocity, the diameter of onion rings zone and the upward displacement of its peripheral metal in the weld thickness direction increases at first and then decreases. With the increase of the welding speed, the diameter of onion rings zone and the upward displacement of its peripheral metal in the weld thickness direction decreases. When welding speed varies in the range of 47.5mm/min～118mm/min under the same n/v ratio, it is conducive to improve the quality of the weld with low welding speed. It is beneficial to form compact weld with the increase of plunge deepness, however, it is easy for the metal on the surface of the weld to overflow with excessive plunge deepness. Keeping a certain clearance between the tip of the pin and back plate is favorable to form the weld with good back appearance, there is lack of penetration at the bottom of the weld if the clearance is too large.Simulation results indicated that, there is circular transfer of the plastic metal in the weld thickness direction, the plastic metal around the left hand thread pin moves downwards, its peripheral metal moves upward; the plastic metal around the right hand thread pin moves upwards, its peripheral metal moves downwards.