Microstructure And Properties Of 7A04 Joint By Pulse TIG Welding Process

7A04 high strength aluminum alloy,as an important light-weight substitute material,has broad prospects in aerospace,national defense construction and other fields because of its high specific strength.In this paper,pulse TIG welding of 7A04 aluminum alloy was studied.The welding arc and mechanical properties and microstructure of joint under three current waveforms(rectangular wave(RW),sinusoidal wave(SW)and triangular wave(TW))were analyzed by optical microscope,industrial X-ray defect detector,scanning electron microscope,universal tensile testing machine and microhardness analyzer.The effect of ER5356,ER5183 and homogeneous welding wire on microstructure and properties of 7A04 aluminum alloy pulsed TIG joint were studied.Periodic changes of different current waveforms lead to changes in the effective value of the welding alternating power.Compared with rectangular wave and sinusoidal wave,when the output current was pulse TW,its effective value was the largest,measured by KEYSIGHT oscilloscope.The change of the effective value of the welding alternating power affected the interaction between the positive polarity and the reverse polarity of the welding.High-speed photography observed that the TIG welding arc presented a "bell jar shape",in which the arc shape of the TW changed more frequently.Moreover,the high frequency arc shape of periodic expansion and contraction promoted the stirring of the molten pool and the refinement of the grain structure.Different current waveforms have different stirring effects on the molten pool of TIG welding.The second phase particles in the welding center were fine and dispersed using pulsed TW current welding under the same process parameters.It can increase the hindering effect on the pinning of dislocations and grain boundaries.Therefore,its yield ratio of the joint is 95%.ER5356,ER5183 and homogeneous welding wire were used to pulse TIG on 7A04 aluminum alloy using TW welding current.The results showed that the hardness values of the weld and heat-affected zone obtained by the 7A04 homogenous welding wire were the highest,followed by those employing ER5183 welding wire.At the same time,the tensile strength of the joint filled with 7A04 homogenous welding wire was up to 245MPa.The change of the 7A04 aluminum alloy welding fusion ratio was achieved by changing the distribution of the welding arc heat input to control the melting rate of the base metal and the welding wire using pulsed TW welding current,which can reduce the hot cracking tendency of the welded joint.Analysis of the morphology and composition of the joint fracture of the 7A04 homogenous welding wire showed that the joint fractured at the Mg-Al phase,and the Zn element was dispersed in the weld.