Research On Flowing Patterns And Thermal Cycles Of Friction Stir Welding Based On MORFEO

The finite element simulation codes MORFEO was used to analyze the effect ofboth the geometry of the pins and the rotation speed on the flowing patterns of4mmthick2024-T3aluminum butt joint in friction stir welding (FSW), and the thermalcycles were also investigated. In the analysis of flowing patterns, the rotation speedwas500rpm,600rpm,800rpm and980rpm with the welding speed of80mm/min, andthe pins were cylindrical and conical. The simulation results shows that particles ofdifferent layers along the thickness of the workpiece are deposited on both sidesbehind the stir tool, when the conical pin and600rpm are utilized. Particles on theadvancing side (AS) flows around the front of the pin to the back of the pin alongwith the particles on the retreating side (RS). However when other weldingparameters are utilized, particles can only get to RS, leaving large vacant space on ASbehind the pin. The marker experiment was conducted to verify the simulation results.The copper foils are bent and smashed which is similar to the simulation results. Themicrostructure adjacent to the bending foil is stretched, depicting it the characteristictexture in the thermomechanical affected zone (TMAZ).2024-T3and7075-T6aluminum were also used in the marker experiment ofT-joint and overlap joint to observe the material flowing characteristics in FSW. Inthe experiment of T-joint, similar circumferential flowing as it in the butt joint wasobserved in the skin. The material of skin and stringer is blending through acomplicated staggered way of axial flowing. Due to such axial flowing patterns, ittends to form a “dead zone” in the “fillet zones”. Thus tunnel defects may appearbecause of the insufficient material flowing. Material in the overlap joint mainly flowsaxially. Material on AS tends to move to the upper centerline, whereas material of theupper and lower plates on RS moves in different direction. Material on the upper platemay move to the lower centerline. Material on the lower plate is forced to the upperplate due to the pin and adjacent colder material.Thermal cycles of the4mm thick2024-T3aluminum butt joint were analyzedwhen the welding speed was80mm/min and the rotation speed was600rpm. It canbe seen that at the beginning of the welding, the workpiece around the stir tool isheated rapidly and the peak temperature is450℃high. As the welding period continues, the temperature rises more slowly and the peak temperature is a little lower.An elliptic isothermal region is also observed, with a wide temperature interval behindthe stir tool and a narrow interval in front of the tool. By using the software MORFEO,verified simulation results of flowing and thermal cycles are obtained. The modularparameter setting and flexible material document makes the simulation procedureindependent from experimental measurement, which brings guidelines to FSWprocess.