Research On Weldability And Welded Joint Structures Of 7075superhard Aluminum Alloy

Aluminum and its alloys have been widely used in the industrial field,which the output is only to the second largest class of metal materials.At present,the 7075 superhard aluminum alloy occupies a very important position in the development of aerospace,because of its high specific strength,excellent processing performance characteristics.However,due to the weldability of 7075 superhard aluminum alloy is very poor,welded joint often appear hot cracking,porosity,other welding defects and joint softening phenomenon,affecting its extensive application.Therefore,through the use of different welding materials,the adjust of the welding process parameters and process measures,the effect of welding materials,process parameters and technological measures on the weldability and joint microstructure of 7075 superhard aluminum alloy were studied.In this paper,the welding process for 7075 superhard aluminum alloy was conduced by two types of ER4043 and ER5356 welding wires under different welding conditions,performance testing and microstructure analysis of weld joints were obtained,to determine the appropriate welding material and process parameter for 7075 superhard aluminum alloy.The orthogonal experiment with an external longitudinal AC magnetic field was carried out,to study the effect of magnetic field parameters and welding process on the weldability and microstructure properties of the joint.The experimental results show that as follows:(1)The welded joint with ER5356 welding wire(short for ER5356 welded joint)is better than that with ER4043 welding wire(short for ER4043 welded joint)in mechanical properties and microstructure.With the increase of welding current,the mechanical properties of welded joints increase firstly and then decrease.When the welding current is increased to 120 A,the mechanical properties of ER4043 welded joint reach the maximum: ?b=287.4MPa,?=3.85%,the weld hardness is 96.7HV,and the low melting point eutectic Si in the weld can reduce the crack susceptibility.When the welding current is increased to130 A,the mechanical properties of ER5356 welded joint reach the maximum: ?b=310.0MPa,?=4.44%,the weld hardness is106.3HV,and the formation of magnesium element strengthening phase improve the microstructure performance and weldability of the 7075 superhard aluminum alloy.(2)ER5356 wire is used for orthogonal test to determine the optimum welding process and magnetic field parameters.When the welding current I=130A,the magnetic field current Im=3.0A and the magnetic field frequency f=40Hz,the mechanical properties of welding joint reach the optimal: ?b=342.5MPa,?=5.63%,the hardness is 112.2HV.Compared with the welding properties of the same welding process without applied a magnetic field,the microstructure is obviously improved,and the weldability of the 7075 superhard aluminum alloy welded joint is enhanced.(3)External longitudinal AC magnetic field by the electromagnetic force act on the welding arc and molten pool.On the one hand,the movement of charged particles make the arc rotate,producing lectromagnetic stirring effect,which refine the weld grain.On the other hand,the movement of charged particles changes the welding arc shape,balancing the molten pool temperature and reducing segregation.Based on the above reasons,the 7075 superhard aluminum alloy weldability and microstructure properties of welded joint are improved.