Experimental Investigation Of Tungsten Inert Gas(TIG) Welding Process On Aluminum Alloy For Improved Mechanical Behavior

The TIG welding of aluminum alloys induces a significant loss in mechanical properties,which is considered a very critical industrial problem that restricts the applications.Therefore,post-welding heat treatment（PWHT）is a compulsory operation to restore properties up to a certain percentage for structural utilizations.The presented study is focused on providing the improved mechanical behavior of the TIG welding process in a single-stage operation.In this regard,the work is directed towards the integration of TIG welding with the nano-materials（NMs）for providing an intelligent way to control mechanical behavior.The investigation started with the novel and the distinctive formation of second-generation fillers.AA6061 tubes have used that section in the symmetrical geometry from the middle through wire electric discharge machining.The inside surfaces of the tubes were coated with multicomponent（two types）functional NMs,which include MWCNTs and TiO₂.The impact of this novel strategy execution on mechanical behavior is summarized in four sections;（1）Aluminum AA6061 rolled sheets（5mm）were used as the base materials（BM）that machined with a V-shaped groove at an angle of 80°to assess the properties.The sequential series of work is designed using the TIG welding operation to find the variation of MWCNTs-TiO₂ and welding current on welding strength.The experiments were carried out at three gradually increasing weight percentages（wt%）of MWCNTs（1wt%,1.5wt%,and 2wt%MWCNTs-TiO₂）that conjugate with fixed 1wt%of TiO₂.The above-stated wt%of MWCNTs-TiO₂ is integrated with three increasing levels of welding current（160A,180A,and 200A）.The tensile test results have depicted a significant improvement within the range of 34.20-46.65%utilizing the second-generation MWCNTs-TiO₂ coated filler in contrast to without NMs.Moreover,the generic U or V shape microhardness hardness profiles have been converted into distinct W-shape profiles representing the uplift of hardness in the welded zones at 1.5wt%and 2wt%contents of MWCNTs.Hence,the primary results have proven the above strategy virtuous in encountering the fusion mechanical property losses in heat-treatable aluminum alloys（AA6061）.（2）In the next stage,a comprehensive microstructure evaluation,%elongation,and fracture behavior were exemplified under the application of MWCNTs-TiO₂ inducement.A pictorial model has been outlined to describe the change in microstructural behavior resulting in MWCNTs-TiO₂ in the weldments.Three types of behaviors are evident,which include pure epitaxial or axial growth,forestry type morphology,and inter-dendritic particles filled in the grains sequentially for without NMs,low wt%of MWCNTs at low heat input,and high wt%of MWCNTs with high welding current levels.Apart from the increasing trend in（ultimate tensile strength）UTS,the welded joints have demonstrated an upsurge trend for%elongation for NMs inducement in contrast to without NMs.The obtained results have illustrated an increment of 71 to 76%and 67 to 75%of elongation at UTS and fracture point for 1wt%and1.5%addition of MWCNTs-TiO₂（at 180A）in comparison to BM.Moreover,the resultant fracture features on the surfaces portrayed large elliptical-shape dimples that have formed at the center position in resemblance with cup and cone type ductile fracture behavior representing an isotropic flow of fractured surfaces.This caused the material flow and deformed plastically,which stimulated extreme convergence on the longitudinal sides of specimens towards the transverse direction.（3）The effect of input effectual variables;MWCNTs-TiO₂ and welding current,involving three levels for each parameter were under-investigated to obtain the response on tensile strength（TS）and grain size（GS）.The full factorial design model has been selected to investigate these 2-factors each at 3-levels（1wt%,1.5wt%,2wt%MWCNTs-TiO₂;160A,180A,200A welding current）by forming 3²（3^k）factorial design.From the analysis,it is quite vibrant that both the TS and GS are significantly influenced by the variation in welding current and inducement of MWCNTs as heterogeneous nucleation.Generally,a gradual reduction in GS is concluded with the increase in wt%of MWCNTs.However,from the analysis of variance（ANOVA）,it is confirmed that the individual and the interacted effect of both the selected parameters had created a significant effective response in the reduction of GS and increment for TS.The obtained high F-values and P-values（P<0.05）from AVONA Table have declared the above statement correct in selecting the significant factors from the analysis.Moreover,a second-order polynomial equation has been employed to develop a regression model that could fit-in the appropriate relationship of the input variable（MWCNTs-TiO₂ and welding current）with the output responses（TS and GS）.In order to check the adequacy of the developed models,high values of R²（coefficient of determination）,（R² 94.86%for TS,R² 97.54%for GS）,implies that the suggested model could fairly be used for the prediction of outcomes concerning to the input variables.Since two independent output responses（TS and GS）scrutinized,the desirability function approach has been incorporated in the system for obtaining the multiple response optimization（MRO）that yields a combined optimized set of process parameters for both.（4）The generation of heat from welding torch that reduces the mechanical properties also generated distortion,which is considered one of the sizable concerns from the quality assurance point of view of the weld.Moreover,this uneven temperature field causes rapid heating and cooling created a geometrical distortion in the system,which leads to fitting problems in the final assemblies.From the analysis,the addition of multicomponent（MWCNTs-TiO₂）NMs has led to an immense reduction in the magnitude of geometrical distortion.The scrutinized behavior has reported a decrement in distortion value with every step increasing wt%of MWCNTs-TiO₂.Since the coefficient of thermal expansion（CTE）is the magnitude of expansion when welded the materials from TIG welding torch,and would raise the susceptibility under the increasing set-in welding current.The mechanism involves the utilization of MWCNTs that limits the distortion attributed to the enormous mismatch in-between the CTE of MWCNTs and AA6061.In values,up to 33.094%reduction was reported from 2wt%MWCNTs at 180A of welding current.The second component（TiO₂）from multicomponent NMs is extremely beneficial on weld depths,the results revealed the radiating radii of profiles with increasing weld depth penetrations.Apart from different theories,Centripetal Marangoni Convection and the constriction of the welding arc column are the responsible mechanisms for overall improvement in geometrical behavior.However,the extended drive phenomenon also includes the electrical resistance effect due to TiO₂ addition,which provokes the constricted melting of fillers.