Research On FSLW Process Of Thermoplastic Polymer And Aluminum Alloy By Ultrasonic

In the field of aviation,the use of polymer and aluminum alloy hybrid structure can significantly reduce the weight of the structure and greatly improve the maneuverability of the aircraft.Friction stir welding(FSW)has the characteristics of low thermal input,which can increase the mechanical mixing of joints.Therefore,FSW has the advantages for the bonding of metals and thermoplastic polymers.However,there are usually some problems in the joining between metal and polymer,such as poor surface forming and low tensile properties.In this paper,ultrasonic and stationary shoulder composite assisted process is proposed to join metal and polymer.The forming and properties of the joint in welding are controlled,and the forming,tensile properties and fracture path of the joint are analyzed,and the bonding mechanism between metal and polymer is revealed.In this paper,the polymer and metal were joined by friction stir lap welding(FSLW),and the polymer is employed as upper sheet.During the FSLW process,more polymer spilled on the surface of the weld,resulting in insufficient material of the weld.Cavity defects are easily appeared in the stirred zone,which seriously reduces the effective bearing area of the joint,and thus the joint tensile shear strength under the conventional process is low.The stationary shoulder has the characteristic of rolling,which can provide a downer force for the joint during welding,and resulting in the joint with a smooth surface,which can effectively reduce the internal defects of the weld.In addition,the stationary shoulder can increase the size of the aluminum anchor structure and promote the bending of the aluminum anchor structure to the outside of the SZ.Thereby the mechanical interlocking capability of the joint can be increased.The mechanical interlocking is the main mechanism of the metal to polymer joining.Under the ultrasonic-stationary shoulder assist process,the thermal action,strong vibration effect and acoustic cavitation effect of ultrasonic can effectively increase the size of aluminum anchor structure,the effective lap thickness of the joint,and the mixing degree of the internal materials of the joint,and the strength of the joint can be improved obviously at lower speed and higher welding speed.Therefore,ultrasound is beneficial to broaden the welding process window.