Study On The Microstructure And Properties Of Friction Stir Welding Joints Of AZ61A Magnesium Alloy

Magnesium and magnesium alloys have low density,high specific strength and rigid damping,excellent shock absorption and thermal conductivity,dimensional stability,low cost,electromagnetic shielding and strong radiation resistance,recyclable recycling,etc.,as an important engineering materials used in the automotive,electronics,shipbuilding,rail transportation,aerospace and other fields have a wide range of applications and development prospects.Due to its low melting point and boiling point,high linear expansion coefficient and thermal conductivity,chemically lively,magnesium alloys are prone to problems such as coarse grain,oxidant combustion,large welding deformation and thermal stress,stoma,cracks,excessive heat affected zone,softening of joints and so on when welding,difficult to obtain excellent weld joints.Therefore,magnesium alloy welding problems has become one of the important technologies that restrict the application and development of magnesium alloys.TIG welding is currently the most commonly used welding method for welding magnesium alloys.It is under the protection of an inert gas atmosphere,utilizing the arc heat generated between the tungsten electrode and the workpiece to melt the base metal and the filler metal.The size and deformation of the heat-affected zone of the TIG welding are relatively small,and the mechanical properties of the weld are relatively high.The friction stir welding(FSW)is a purely mechanical solid-phase connection method and compared with the fusion welding,good mechanical properties of welding workpiece,no need to protect gas and solder,less preparatory work before welding,small deformation after welding,all-position welding,etc.,especially suitable for welding magnesium alloys.In this paper,the microstructure and properties of TIG welding and FSW welding joints of AZ61A magnesium alloys with two thicknesses were studied by means of tensile,bending,metallographic analysis and hardness tests.Through pulsating tensile fatigue tests,The fatigue properties of welded joints of AZ61A magnesium alloys were tested and studied.The median fatigue strengths of TIG welding and friction stir welding joints were compared and analyzed.The results show that the joints of TIG welding and FSW of AZ61A magnesium alloy have good tensile properties and bending properties,meeting the requirements of the standard,4mm thick AZ61A magnesium alloy TIG welding joints' tensile strength and FSW joints' tensile strength is not much difference,the tensile strength of 6mm thick FSW joints is 21 MPa higher than the TIG welding joints;The microstructures of the weld joints are composed of a(Mg)phase and P(Mg17Al12)phase,but their morphology and distribution are different;The hardness of the joint weld zone and the base metal zone are not much different,and they are all produced different degrees of softening in the heat affected zone;The median ultimate fatigue strength ?0.1 of AZ61A magnesium alloy welded joints:the fatigue strength of the butt joints of 4mm and 6mm AZ61A magnesium alloy TIG welding were 77.5MPa,and the fatigue strength of butt joints of FSW were 115MPa.