Friction Stir Welding Of Aluminum Alloy Thin Sheets Assisted By Rotational And Stationary Shoulders

As the main weight-reducing material,aluminum alloy has been increasingly used in modern industries.Joining aluminum alloys was always a problem.Voids,cracks,and hot distortion always appear in fusion welding joints,reducing joint mechanical properties.Friction stir welding(FSW)is a solid state joining technology.The peak temperature is lower than the melting points of the base materials during FSW.Therefore,FSW is suitable to join aluminum alloys.Friction stir lap welding was used to join 2024-T4 thin sheets.The effect of welding parameters on the microstructure and mechanical properties were mainly studied.Firstly,conventional friction stir lap welding 2024 thin sheets was studied.Sound joint was obtained under this condition.Defects such as shoulder marks and flashes were observed.There existed a continuous bonding ligament in the joint center.No crack was observed inside the bonding ligament.Hook and cold lap presented slight upward bending morphologies.The hardness curve presented a typical W shape.The maximum value located at the base metal and the minimum value located at the heat affected zone.With increasing the rotating speed,the maximum failure loads were obtained at 600 rpm,which were 2330 N(AS)and 6419 N(RS).Rather complicated trend was obtained by changing the welding speed.The maximum load of 3723 N was obtained at 100 mm/min when the AS bore the main load.The maximum load of 6932 N was obtained at 200 mm/min when the RS bore the main load.Secondly,the stationary shoulder friction stir lap welding thin aluminum alloys sheets were studied.Stationary shoulder successfully eliminated the flash and shoulder marks.There smooth joint surface was obtained.The stationary improved the material flow behavior.The bonding ligament was broken and onion ring was observed in the joint.The heat affected zone and thermal-mechanically affected zone were narrower.The lap shear properties of the joint using the stationary shoulder were higher.The failure loads of the joints firstly increased and then decreased no matter which side of the joint bear the load.The maximum loads were 5593 N(AS)and 6702 N(RS).Similarly,the maximum loads were obtained at 200 mm/min,which were 6475 N(AS)and 7440 N(RS).At last,aluminum alloys sheets were lap welded assisted by rotational and stationary shoulders.Sound joint surfaces were obtained under this condition.The stir zone was narrower than that using the conventional lap method,and wider than that using the stationary shoulder.Failure loads of the joints firstly increased and then decreased by changing the rotating speed.The maximum loads of 5364 N and 5291 N were both obtained at 600 rpm.The maximum failure loads were obtained at 150 mm/min and 100 mm/min by changing the welding speed,which were 4263 N(AS)and 6701 N(RS).