Study On Microstructure And Properties Of 2A12 Aluminum Alloy By Ultrasonic Assisted TIG Welding

TIG welding is widely used in the welding process of aluminum alloy because of its beautiful weld,simple operation and so on.However,there are some disadvantages,such as hot crack and serious tendency of porosity.The ultrasonic method is introduced into the base metal directly through the base material,which overcomes the disadvantages of low utilization rate of ultrasonic energy and unstable arc in the arc ultrasonic method.At the same time,it has many advantages,such as inhibiting hot crack,refining grain and removing bubbles,etc.,which can produce more effect on Microstructure and mechanical properties of weld.In this paper,the effect of ultrasonic power on weld formation,microstructure and mechanical properties of TIG aluminum alloy by ultrasonic assisted welding was studied.Firstly,the regularity of weld formation and microstructure in ultrasonic assisted TIG surfacing test was studied,and the thermal cycling curve of the bath before and after applying ultrasound testing was tested.The results show that the ultrasonic intervention accelerated the heat transfer,shorten the duration of the molten pool,and increased the cooling rate,and changed the weld formation of 2A12 aluminum alloy,the formation of hot cracks is restrained,the nucleation rate increases,the grain morphology changes from cellular crystal to equiaxed crystal,the grain is refined,the eutectic structure tends to be uniform,and the hardness and tensile properties of welded joint are improved.Study on the ultrasonic after welding on the vibration amplitude distribution and rules using ANSYS software.The results show that the amplitude of the weld formation,grain refinement and mechanical properties significantly affected.Secondly,the influence of ultrasonic assisted TIG welding on the macro morphology and microstructure of ER2319 and ER5356 joints was investigated.The flow velocity and flow direction of molten pool were studied by FLUENT fluid analysis.The results show that the ultrasonic treatment changes the morphology of the?-Al grains in the weld formation process,and makes the grains of each zone of the weld be refined effectively and the pores are removed.With the increase of ultrasonic power,the cross section of a joint fusion zone gradually narrowed,?-Al grain from coarse columnar to equiaxed transition,transition weld center?-Al grain from dendrite,columnar to equiaxed and spherulite;After the solidification of the weld longitudinal section,the?-Al grains change from coarse columnar crystals to equiaxed grains,and the central region changes from cellular crystals to spherulites.The structure,morphology and distribution of the second phase in ER2319 and ER5356 joints were analyzed by ultrasonic assisted TIG welding.The precipitation phases are determined as??Al₂Cu?and S?Al₂CuMg?phases.The difference is that the Mg element precipitation in the second phase of the ER2319 weld increases after the ultrasonic is applied,but the precipitation of Cu element in the second phase of the ER5356 weld increases.And without ultrasonic weld phase along the grain boundary?-Al long strip-shaped precipitation,its size is large.Second?-Al along the grain boundary and grain internal reticular dispersion after the application of ultrasonic,its size decreases.Finally,the mechanical properties of ER2319 and ER5356 joints were tested by ultrasonic assisted TIG welding,and the mechanical properties of the two joints were compared and analyzed.It is found that the hardness of the joint increases with the increase of ultrasonic power,and the hardness of 1000W is the highest,while the tensile strength and elongation reach the optimum at about 800W.By comparison,the hardness and elongation of ER2319 joint are higher than that of ER5356 joint,and the tensile strength is lower than that of ER5356 joint.