Study On Microstructure And Properties Of 5356 Aluminum Alloy By Tig Welding Under Pulse And Swing Conditions

The low cost,high efficiency and rapid net forming of large and complex components are the important development direction of manufacturing technology,which plays an irreplaceable role in the aviation,aerospace,automotive,and energy industries.Additive manufacturing is a new technology without molds that can directly manufacture complex components at low cost.Its superior configuration capability makes it easy to solve the problems which are difficult to achieve by using existing manufacturing technologies of structural and functional integrated manufacturing.Thesis focuses on the arc additive manufacturing of 5356 aluminum alloy structural parts,studies the solidification mechanism of the bonding layer and deposition layer and the effect of heat input on the microstructure and properties of the specimen,which has important theoretical significance and application value.5356 aluminum alloy wire was used as material and arc addition experiments were carried out.According to the result of analyzing macroscopically morphology,microstructure and mechanical properties of the different surfacing structural parts,we obtain better welding process parameters.The microstructure and mechanical properties of the formed parts in different regions and sampling directions were analyzed on this basis.The experimental results show:the deposition layer and the bonding layer of the surfacing are formed alternately,the grain sizes of the top,middle and bottom are the same,there are a large number of defects such as pores and shrinkage holes in the bonding layer and no significant welding defects are observed in the deposition layer.The mechanical properties are approximately equal at different sampling positions horizontally,the average tensile strength and elongation are 274.0 MPa and 32.3%respectively.There is no obvious change of strength and plasticity between vertical direction and horizontal direction.The fracture analysis shows that uniform plastic fractures occur in different directions and sampling positions,the vertical tensile fracture is observed at the interlayer,which is the weakest part in the entire structure.Thesis compares the changes in microstructure and properties of surfacing structures welding by AC heat input with and without pulse.The results show that the grains of the ac-formed samples are coarser,the pulse current reduces the heat input during the forming process and the grains are refined,which improves the strength and plasticity of structural component.The grain size of the formed part welding with pulse is between 50～100μm,which is about half of that without pulse;at the same time,the pulse current makes the β-Al3Mg2 phase more evenly dispersed and the size is smaller.Compared with welding without pulse,its strength and elongation increase by 10.9 MPa and 5.8%.The difference of hardness between two heat input methods is small,and the hardness value of the deposition layer is kept at a stable variation range.The hardness of the bonding layer is greatly fluctuating due to defects such as pores and shrinkage holes and the value is lower.The influence of forming quality with swing forming path was studied.The results show that the weaving forming organization not only has the striped topography between the deposition layer and the bonding layer,but also the swinging joint layer can be formed by the reciprocating swing.The microstructures of different forming positions are different.The upper layer is mainly composed of columnar crystals,the central region is mainly equiaxed,and the lower region consists of columnar crystals and equiaxed crystals.Comparing the mechanical properties of the structural parts welding with and without pulse and swing forming method,the results show that the performance of the parts with pulsed AC welding is the best,the second is performance of swing forming,the worst is the pulseless AC forming,the average tensile strength of the welding parts with pulsed AC forming is 277.5 MPa while the elongation rate is 31.0%.The completion of the paper provides theoretical basis and technical support for micro structure design and performance control of aluminum alloy by wire arc additive manufacture.