Experimental Investigations On Deformation Behavior Of Rolling As-welded Magnesium Alloy Thin Sheets Joined By Friction Stir Welding

Magnesium alloys have many advantages,such as low density,high specific strength,high specific stiffness and electromagnetic shielding.They are widely used in electronic industry,automobile industry,aerospace industry and military.The preparation of large rolling coils,high performance and wide width magnesium alloy rolls is one of the important development goals of light alloy materials.The head-to-tail welding of magnesium alloy sheet is a method of continuous coil,which can not only increase the length of magnesium alloy strip,but also provide continuous thin sheet rolling blank to realize heavy coil rolling of magnesium alloy strip.The performance of the joint of magnesium alloy strip is lower than that of base metal after welding.The welded joint is not suitable to bear excessive load,as well as plastic deformation.For the rolling problem of magnesium alloy welded strips,it is necessary to systematically study the deformation behavior of welded joints with different rolling reduction,realizing the engineering applications and the significance of thesis research.In this paper,the deformation behavior of welded joint of AZ31 magnesium alloy sheet during warm rolling was studied.The microstructural evolution and property changes of plastic deformation of welded joint were investigated by using friction stir welding and rolling process.Firstly,the initial Friction Stir Welding(FSW)joint strip of AZ31 magnesium alloy was obtained,and then the welded strip was processed by multi-pass warm rolling at 220-240?.By metallographic microstructure,mechanical properties and texture of as-rolled-welded plates with different reduction,the deformation behavior of friction stir welded joints during rolling was analyzed,and the feasibility of increasing coil weight by connecting magnesium alloy coil strips was discussed.The main results are as follows:(1)Welding parameters: welding rotation 1 400 rpm,welding speed 15mm/min,axis force 2-4kN,inclination angle 2 degrees;The welded joints have regular shape,smooth surface and no internal defects.Friction stir welding(FSW)is a suitable way for joining magnesium alloy sheets.(2)No strip breakage occurs during tension rolling of AZ31 welded sheet without reducing rolling speed and rolling force,and plastic deformation occurs simultaneously between welded joint and base metal.The coarse grains in full of welded joints break up and grow up again.The uniform structure and stable mechanical properties of weld zone and base metal can be obtained again after rolling.(3)The uniaxial tensile fracture of the welded joint is located in the heat engine affected zone of the front side.The front side of the welded joint has stronger texture than the back side.It is easier to deform under stress.After rolling,the grain anisotropy of the welding position is weakened,and the homogeneity of the structure in the welding zone is improved.The mechanical properties of the deformed welded joints are up to 80% of the base metal.(4)Friction stir welding can be reasonably applied in continuous rolling process of magnesium alloys to get the heavy coil rolling of magnesium alloy strips and then improve production efficiency.