Abstract
Friction stir welding (FSW) is a solid-state metal joining process. There is no melting and recasting of metal while welding is used. Some of the defects commonly encountered in FSW are tunnel defect, bond, cracks, pin holes, and pipping defects. The defects occur because of improper metal mixing and less heat input in the weld nugget zone. In the fusion welding process, a filler rod is employed to form a quality weld with superior mechanical properties. In this work magnesium and chromium powders are used as filler materials. The purpose of this study is to ascertain whether filler materials and manufacturing processes have an impact on the weld nugget zone spot weld joint formation as well as the mechanical and abrasive properties of welded joints. This study's FSW filler materials mixing ratio and process parameters were improved by using the Central Composite Design (CCD) idea, which is discussed in more detail below Response Surface Methodology (RSM). The best empirical relationship between the parameters was provided by the CCD. The mathematical relationships were established to forecast the maximum tensile strength, maximum weld nugget hardness, and minimum corrosion rate by incorporating filler materials with process parameters. The optimal processing factors combination is predicted by conducting the validation test. The optimum parameters were the tool rotatory speed 600–1000 revolution per minute, welding speed 60 to 180 mm/min, plunge depth of 0.05 to 0.25 mm, center distance between the sample is 0–4 mm, as well as powder mixing ratio of 90 : 10, 92.5 : 7.5, 95 : 5, 97.5 : 2.5, and 100 : 0, the tensile test, microhardness, and corrosion rate analysis were conducted on the weld specimen. The welded test specimen provides better joint strength, weld nugget hardness, and enhanced corrosion resistance properties. The microstructure analysis shows the fine grain structure and homogeneous distribution of filler material with the base metal in the welded area.
1. Introduction
Welding is a critical step in the production process in which metals are fused together. Metal joining inventions have been bolstered by advances in metals and metal joining technology. Many industrial applications have seen a constant progress as a result of this. Bonding takes place at the original boundaries of the components during welding. It is heated to molten condition, and then allowed to cool down. There are two fundamental types of these processes: fusion welding and solid-state welding. Heat is utilised to melt the base metal during the fusion welding process. If you want a stronger joint, it is essential that the molten pool be enriched with additional filler metals. Arc welding, gas welding, resistance welding, laser beam welding, and electron beam welding are just a few of the common fusion welding methods. By applying pressure to the sites of contact, solid-state welding unites two metals at a temperature below their melting point.
The advancement of aluminum's pulsed GTAW technology and the primary properties of welds made of the AA 5154 alloy. The authors were identified that the use of current pulsing reduced the size of dendrite cells though improved mechanical properties were achieved [1]. Also, the use of helium gas as a shielding gas during pulsed GTAW of aluminium reduced the number of porosities, solidification cracking susceptibility, and weld distortion. In the postweld ageing of an AA6063 aluminium friction stir weld, the precipitation sequence is identified [2]. FSW has been shown to create a softened weld area. A minimum hardness zone is seen in the dissolved region. It has been discovered that hardness increases with postweld ageing. He conducted postweld ageing at 443 K.
After 12 hours, it was discovered that the welded area had a higher hardness level. The mechanical characteristics of Al-Si-Cu-Mg alloys were compared [3]. It was found that when the concentration of Cu and Mg is raised, the material’s ductility decreases while its strength and ductility improve. The joint qualities of different cast A356 and wrought AA6063 were investigated by Cavaliere et al. [4], who changed the fixed location of the materials to alter the joint properties. For AA6063, the stir zone strength is larger than that of A356 when put on the retreating side during longitudinal tensile tests. When solution hardening, grain boundary migration happens because of an imbalance among thermodynamic driving forces and pinning forces, which causes grain expansion. Through solution heat treatment, the pinning forces are said to diminish as the solution temperature rises. The precipitate stages break down and the grains become coarser as the pinning forces decrease. As the temperature of the solution rises, so does the precipitate’s dissolvability and coarsening.
AA 5154 aluminium alloy was utilised by Feng et al. [5] for FSW under various conditions, which include tool design and rotational and translational speed. According to microstructural, mechanical, and residual stress tests of four Al alloys AA 5154, thermal input rather than tool deformation affects welding parameters. To better understand the impacts of postweld heat treatment on 2219-O aluminium alloy microstructure and mechanical characteristics, Mindivan et al. [6] conducted a series of tests, tensile tests of heat-treated regions increase as solution temperature rises, up to 260% greater than the base metal’s (BM) maximum allowable tensile strength.
Dissimilar friction stirs welded aluminium alloys enhanced with nano additions were studied [7]. Electrochemical methods were used to test the corrosion resistance of samples with and without nanoparticles. It is thought that the addition of MBT to CeMo containers during FSW increases the final material’s corrosion resistance because it forms stable complexes with the alloying metals that prevent chloride from penetrating the AA surface.
Three different aluminum alloys, Al1050-H24, Al 6061-T6, and AlAA 5154-O, have the FSW. From the mechanical and metallurgical analysis, Al1050 consists of low deformation resistance and due to which the FSW joint made by a cylindrical pin tool exhibits high mechanical properties than the other types. But the shape of the tool pin does not affect the weldment microstructure and mechanical characteristics of 6061-T6 alloy weld joints [8, 9]. Deformation resistance in the FSW temperature range is relatively low for high melting temperature metals, hence cylindrical tools are better suited for these materials. But, also it is suitable for high deformation-resistant material with low rotational speed.
FSW properties and microstructural changes in aluminum alloy 6063-T6. A correlation between the tensile properties of the joints and a process parameter was examined according to their intended use and methodology. They used optical microscopy and microhardness measures to analyse the microstructures of several zones of FSW. Test welds mechanical resistance was observed to rise as welding speed was amplified at the same rotating speed [10]. They detected the source of tunnel (wormhole) faults in the weld nugget and the HAZ of an entity lower than that of fusion welds. In their tests, they used a variety of process parameters, but they could not regulate the downward force on the weld. Various parameter combinations were tested to see how far they could be taken. When welding speed is raised, the improvement in mechanical resistance provides an immediate economic benefit [11].
The characteristics of an FSW joint made of Al alloy with less porosity, fine microstructures, limited phase transition, and low oxidation to those of traditional welding techniques. They created FSWs of Al alloys AA 5154-H18 and 6111-T4 using certain FSW settings, and they measured the physical weld flaws [12]. Tensile tests and hardness dimensions were utilised to determine the microstructure of the weld and the BM, and these results were then correlated. They discovered that the AA 5154 specimens’ stir zones are significantly softer than the strain-hardened foundation materials. Compared to the basic material, the SZs in 6111 are in terms of hardness. They discovered that some of the heat impacted zones of 6111 friction stir welding specimens exhibited natural ageing and hardening for up to 12 weeks following welding [13]. Welds made under specific welding conditions and in specific areas of the weld zone showed aberrant grain growth (AGG) after annealing AA 5154 FSW specimens. AGG is more severe in low-heat conditions, they discovered.
Aluminium alloy 6063-T6 friction stir welds were studied by their characteristics and microstructure. It was determined that the connection between tensile strength test results and a processing factor was high. Microstructures of several zones of FSW were shown and analysed using optical microscopy and microhardness extents [14, 15]. Test welds mechanical resistance was observed to rise as welding speed was increased at a constant rotational rate. Tunnel (worm hole) faults were discovered to be the result of a softening of the material in the weld nugget and the HAZ of an entity lower than that of fusion welding. In their tests, they used a variety of process parameters, but they could not regulate the downward force on the weld. They looked at the possibility of combining and extending the set of applicable parameters.
Friction stir welding of 6111 and AA 5154 aluminium alloys yielded minimal porosity, fine microstructures, and negligible phase transition as well as low levels of oxidation when the welding speed was increased [16]. They employed particular FSW parameters to build FSWs for aluminium alloys AA 5154-H18 and 6111-T4 and then measured the physical weld flaws that resulted. The results of the tensile and hardness tests were related to the weld and base material microstructures. A significant difference was found between the AA 5154 specimens and the strain-hardened foundation materials in the softness of the stir zones. The SZs in the 6111 material have a hardness that is nearly identical to that of the base. According to their assessment of the heat-affected zone of 6111 friction stir welding specimens, this hardening remained for up to 12 weeks after the weld. Erroneous grain growth (EGG)was observed after annealing AA 5154 FSW specimens welded under particular circumstances. EGG is more severe in cooler climates, researchers found [17].
The fatigue fracture propagation behaviour of friction stir welded AA 5154-H32 and 6061-T651 aluminium alloys was investigated [18]. For dynamically recrystallized zone specimens, the stress intensity factor at residual stress (Kres) was used to calculate the residual stress-corrected K, or Kcorr, for FS welded plates that were subjected to residual stress measurements either perpendicular to or parallel to the welding direction. This was done to quantify the compressive residual stress’ contribution to fatigue crack propagation rates. FS welded AA 5154-H32 and 6061-T651 specimens in the dynamically recrystallized zone showed fatigue crack propagation behaviour due to favourable compressive residual stress reduction effective K and detrimental grain refinement inducing intergranular fatigue failure, according to the authors.
The AA 5154 (Al-Mg) is mostly employed in marine environments, building construction, and food processing because of its corrosion resistance performed FSW on the AA 5154 aluminium alloy to discover the ideal process parameter to produce maximum corrosion resistance and mechanical qualities. It was decided to utilise the potentiodynamic polarisation test to see how well the material held up against corrosion [19]. The fine grain structure strengthens the anodic reactivity of the weld nugget. Optimal weld speed and feed resulted in the grain reinforcement and precipitate dissolution in the nugget zone which promotes passive film formation on the nugget portion during corrosion. Hence, high corrosion resistance was obtained.
Underwater FS welded Al AA 5154 alloy microstructure and mechanical behaviour were studied [20]. In this experiment, water-cooled specimens were found to have a much higher hardness of the stir zone than specimens cooled in air. Nan Zhou et al. (2018) studied the mechanical properties and fracture behaviour of AA 5154-H112 friction stir welds in relation to the kissing bond. An extensive welding matrix was used to weld the AA 5154-H112 at speeds ranging from 100 to 300 millimeters per second, with tool rotation rates between 800 and 1200 revolutions per minute. The duration of the kissing bond was influenced significantly by the welding parameters, particularly rotation and feed speeds, and the length of the kissing bond reduced as the welding heat input increased [21]. Tensile and fatigue fracture patterns were also discovered to be affected by kissing bond length and form. These cracks occurred in the welds with long fatigue life and strong tensile capabilities. Those with low fatigue life were found to have fractures in the kissing bond.
Several joint types can be fabricated by friction stir welding (FSW), namely butt-, lap- (overlap-), and T-lap joints (Figure 1) along with the lap joint in the form of spot welding by friction stir spot welding (FSSW).1
Then, to enhance the FSW variables, multiobjective optimization techniques including central composite design and response Surface optimization were applied. This friction stir weld connection of aluminium alloy 6063 and aluminium alloy AA 5154 has been studied only in the context of metallurgical, mechanical, and corrosion behaviour. But, no visible investigation has been completed on FSW connections with filler metal addition to dissimilar material joining of AA6063 and AA 5154 aluminium.
Hence, it is more interesting to investigate the effect of addition of filler to dissimilar material joining of AA6063 and AA 5154 aluminium alloy with regard to its metallurgical, mechanical, and corrosion behaviours. The focus of the current study is therefore on the connection of aluminium alloys such as AA6063 and AA 5154 that have different compositions, as well as the inclusion of filler material. Mg increase in the weld zone improved the weld connections TS.
2. Materials and Methodology
The Al alloy 6063 and AA 5154 were selected as base materials. The fillers magnesium and chromium were selected to introduce between the joints during the welding in powder form. The fillers were stuffed into the holes on butting of the plate to be welded. The tungsten carbide was selected as a tool material. The hexagonal pin profile was preferred for this work due to its good stirring characteristics. The optimum parameters were the tool rotatory speed 1000 revolution per minute, welding speed 120 mm/min, plunge depth of 0.15 mm, mid distance among the holes of 2 mm, as well as powder mixing ratio of 95 : 5 (%). The tensile test, microhardness, and micro- and macrostructure analyses were conducted on the weld specimen.
2.1. Evaluation of Base Metal Composition and Properties
Aluminium alloys AA6063 and AA 5154 were employed as the base metals in this study. The chemical composition of base metals was attained from vacuum spectrometer (ARL-Model3460). A spectroscopic analysis was performed to determine the alloying elements by igniting sparks at various locations on the base metal samples. Table 1 shows the percentage of chemical characteristics of each element in AA515 and AA6063. The physical and mechanical characteristics of AA 5154 and AA6063 are shown in Table 2.
ASTM E8M-04 criteria were used to prepare tensile test samples for base metals. Figure 2 depicts the base metals’ microstructure. Strengthening precipitates are distributed uniformly across the microstructure, which primarily comprises of elongated grains.
2.2. Levels of Process Parameters
The settings for the test runs were derived from references to the literature for AA 5154, AA6063, and a different combination of the two alloys. Trials were completed in order to stabilize procedure parameter and eliminate any visible faults in the joints. Based on these tests, the freezing process parameters were as follows: tool rotating speed of 1000 rpm, welding speed of 120 milli meter/s, and a plunge depth of 0.15 millimeter. The frozen parameter was confirmed by welding three samples together. The strength of the welded junction was put to the test. A total of 147 MPa tensile strength was achieved by this combination. Table 3 shows the tensile strength for the freezing parameters as determined by the trial experiments.
There were a number of variables that were taken into consideration during the experiment. Welding speeds ranged since 600 rpm up to 1400 rpm as well as 60 millimeter/min up to 180 milli meter/min after a series of testing. From 0.05 mm to 0.25 mm, the depth of the plunge was steadily raised in five 0.05 mm steps. It was decided that the center distance would be spaced at intervals ranging from 0 millimeters to 4 millimeters apart along the plate’s butting surface, 2 millimeters and 3 millimeters. In the welding stir zone, the mean wt. percentages of chromium and magnesium are measured. The average wt. percentage of Mg and Cr alloy elements in the weld stir zone was utilised to calculate wt. % proportion. The entire filler wt. was used to compute the Mg/Cr filler % proportion. A 90 : 10, 92.5 : 7.5, 95 : 5, 97.5 : 2.5, and 100 : 0 mixture of Mg and Cr powders was employed. The hexagonal pin profile has a 20 mm shoulder diameter, an 8 mm pin diameter, and an overall 7.6 mm length. Table 4 shows the FSW process parameters, as well as their range and level.
3. Results and Discussion
3.1. Tensile Strength
This test was carried out on 32 FSW samples, and the results are tabulated in Table 5 below.
3.2. ANOVA for Tensile Strength
ANOVA was utilised to assess in developing an actual connection. The ANOVA tests for TS are displayed in the image and are included in Table 6. We can conclude that the model’s F-value of 382.31 is statistically significant. It is impossible for noise to produce an F-value this enormous with a 0.01 percent chance. Modelling terms are considered significant when their p values fall below 0.05. It is important to note that R2, W2, P2, C2, and M2 are all relations of reference in this example. Statistically significant model terms are those with a value greater than 0.1. Weld joint tensile strength is evaluated using the following empirical relationships:
As can be seen from the F-statistic, a failure to fit is not substantial when compared to the total error. Noise has a 13.69 percent probability of causing such a significant inadequacy in the F-value. Less than 0.2 of a difference exists between the expected R2 of 0.9699 and the adjusted R2 of 0.9960. The SN ratio is determined by adequate precision. There should be a ratio of at least 4 is to 1. In this model, a signal strength of 63.916 is considered acceptable. The design space can be guided by this paradigm. Figure 3 shows the FRW process. Figure 4 depicts the tensile sample prior to and following its testing procedure.
3.3. Microhardness
Thirty-two FSW samples were tested for microhardness, and the findings are shown in Table 7. AA6063 and AA 5154 dissimilar alloys are presented for the influence of process factors on the microhardness of each alloy.
Figure 5 shows the weld cross section of the AA 5154-AA6063 dissimilar joint at the AS and RS side showing that the FSZ, the weld’s butting surface was tested for microhardness. As opposed to the moving side, the friction stir zone (FSZ) weld hardness was discovered to be higher, as associated to both advancing and retreating sides. The stir zone weld’s hardness is determined by the welding process’ parameters. The weld’s microhardness was raised, thanks to the stir zone’s grain refining and grain particle size reduction. The manufactured junction with a rotating speed of 600 rpm had the lowest weld hardness measured. As shown in Figure 5, the friction stir zone had the highest microhardness value of 93 HV at the AS side and fine grain structure with 34 HV at the RS side, when the tool was rotated at 1000 rpm. With these parameters are in place, we achieved the highest weld hardness in comparison to any other process parameter levels: welding speed of 120 m/s, plunge depth of 0.15 mm, center distance along 2 mm as well as a 95 percent Mg, 5 percent Cr, powder mix proportion (Figure 6(a)), R-tool rotational speed (rpm) (Figure 6(b)), W-welding speed (mm/min) (Figure 6(c)), P-plunge depth (mm) (Figure 6(d)), C-center distance (mm) (Figure 6(e)), and M-powder mixing ratio (Mg : Cr) (%).
(a)
(b)
(c)
(d)
(e)
3.4. ANOVA for Microhardness
Table 8 displays the results of an ANOVA test to determine the microhardness of a sample. The model’s F-value of 84.15 indicates its significance. A noise-induced F-value this big has a vanishingly small probability of occurrence. Model terms that have a p value below 0.05 are considered significant. Equation (2) represents the final empirical relationship to estimate the microhardness of the weld area.
F-value of 0.767 indicates that the lack of fit is statistically insignificant when compared to the pure error. Noise has a 62.67% risk of causing a substantial lack of fit F-value. The predicted R2 of 0.9124 is regarded fair because the difference between the predicted R2 and the adjusted R2 is lesser than 0.2. The signal-to-noise ratio was assessed using adequate precision. There should be a ratio of at least 4 is to 1.28.7479 as a suitable signal in this model.
Thirty-two FSW samples were tested for corrosion rate, and the findings are shown in Table 9. AA6063 and AA 5154 dissimilar alloys are presented for the influence of process factors on the corrosion rate of each alloy.
3.5. ANOVA for Corrosion Rate
The analysis of variance test results for the rate of deterioration are tabulated in Table 10. Noise has a 0.01 percentage probability of producing an F-value of this size. P values of lesser than 0.05 are considered significant in the model’s terms. As shown in equation (3), the empirical relationships used to determine the weld surface corrosion rate are represented as follows.
Negative values indicate that the terms of reference are insignificant. According to the F-value of 1.04, the lack of fitting is insignificant when compared to the total error. An F-value this enormous could be the result of noise, according to the 49.26 percent probability. The expected R2 of 0.8684 is regarded fair because the difference between the expected R2 and the adjusted R2 is lesser than 0.2. The signal-to-noise ratio is determined by adequate precision. There should be a ratio of at least 4 is to 1. In this model, 23.5417 indicates a sufficient signal.
4. Conclusions
The following are significant findings gained from scientific research of incorporation of Mg and Cr filler in FSW uncoordinated connections of AA6063 and AA 5154:(i)For highest TS, weld nugget hardness, and lowest corrosion rate, a multiobjective optimization of the RSM technique was applied and optimized the friction stir welding parameters.(ii)An ideal input parameter for producing a sound joined aluminium alloy 6063 and aluminium alloy AA 5154 uncoordinated junction is a tool rotational speed of 1,000 rpm.(iii)In terms of tensile strength, microhardness, and corrosion rate, tool rotating speed and powder mixing ratio are the two most important factors.(iv)Weld nugget hardness of 93 HV and corrosion rate of 0.814 mm/y were achieved with the optimal parameter combination of R of 1000 rpm, W (120 mm/min), P (0.15 mm), C (2 mm), and M (95 percent Mg and 5 percent Cr) that was achieved.(v)The joint strength of 147 MPa without filler was obtained by the above parameter combination.(vi)The highest connection strength of 173 MPa was improved by mixing 95 percent magnesium and 5 percent chromium filler. This indicates that the use of filler in friction stir welding results in an 18 percent increase in joint strength.(vii)Joint strength and weld hardness are originally increased by increasing the weight percentage of magnesium and reducing it by decreasing the chromium content in the alloy. A progressive drop in joint strengthening and weld hardness is observed following threshold value of 95 percent Mg and 5 percent Cr is crossed.
Data Availability
There is no data availability statement.
Conflicts of Interest
The authors declare that they have no conflicts of interest.