Microstructure Of Stir Zone Research Articles

Forming control and the relationship between microstructure and mechanical property in TIG-assisted friction stir welded joint of Ti-6Al-3Nb-2Zr-1Mo titanium alloy

In this paper, T-joints of Ti-6Al-3Nb-2Zr-1Mo titanium alloy were joined with friction stir welding, and microstructure evolution and forming mechanism were studied. The effect of using tungsten inert gas welding to heat additionally the FSW was investigated. Results show a strong effection microstructure of stir zone (SZ) due to the temperature gradient and fast cooling rate. The top and middle sections of SZ have a basketweave microstructure, while there is duplex microstructure at the bottom. When welding at 750 rpm-50 mm/min, the maximum tensile strength of the joint is similar to that of the base metal (BM). As the heat input increases, grain coarsening occurs, which reduces the joint tensile strength and the ability to plastically deform. The fracture mode changes from mixed fracture to ductile one. When TIG-assisted heat source is 20 mm in front of the tool and the power input is in 600 W, the temperature field produced is relatively uniform, which has a positive effect on the weld.

Influence of friction stir processing (FSP) on arc directed energy deposited 316L stainless steel: a corrosion science study

Friction stir processing (FSP) was employed as a post-printing surface modification technique to enhance surface properties of arc-directed energy deposited 316L austenitic stainless-steel parts. Corrosion properties and passivity of stir zone and base metal were investigated in 3.5 wt.% NaCl solution. Results reveal a gradual improvement in corrosion protection ability of formed passive film on the alloy's surface over time. Specifically, FSPed region exhibited superior passive behavior and uniform corrosion resistance compared to base metal. This improvement was attributed to a more homogeneous microstructure of stir zone, which hindered micro-galvanic coupling effect. However, it was observed that FSP-treatment did not effectively impede the propagation of pitting corrosion.

Effect of process parameters on weld geometry and mechanical properties in friction stir welding of AA2024 and AA7075 alloys

FSW joints are promising because they have a minimal heat input in welding and can limit the amount of intermetallic compound formation in dissimilar metals. Solid-state welding processes, particularly friction stir welding (FSW), are preferred for welding aluminium alloys due to their low heat input and ability to minimize intermetallic compound formation. This study conducted FSW trials on AA7075 and AA2024 alloys, each 4 mm thick. Parameters such as axial force, rotational speed, and traverse feed were adjusted while keeping other factors constant. The study analyzed weld geometry characteristics, including bead width and penetration depth. Angle distortions during FSW of thin plates in a butt joint were investigated. Additionally, the study examined the effects of FSW parameters on mechanical properties such as tensile strength and hardness immediately after welding. Microstructures of the welds were observed using optical microscopy (OM). The optimal mechanical properties are achieved at a rotational speed of 1000 rpm, a traverse feed of 30 mm/min, and an axial force of 10 kN. This optimal condition facilitates material flow around the pin at an ideal speed, ensuring adequate material filling and preventing tunnel formation. The stir zone's microstructure under these parameters exhibits a finely recrystallized structure with a significantly smaller grain size than the base material. Consequently, this enhances the joint's microhardness and tensile strength.

An experimental method for choosing the tool pin profile and shoulder size to join dissimilar aluminum alloys AA7075-T651 and AA6061-T6 joints

Many military and light weight aircraft designs call for joints between two different grades of aluminium alloy. This present study looked at the effect of tool shoulder diameter and tool pin profile on the tensile strength properties of dissimilar aluminium alloy AA6061-T6 and AA7075-T651 joints created by friction stir welding. The joints were fabricated utilizing three distinct tool shoulder diameters 15 mm, 20 mm and 25 mm along with two distinct tool pin profiles namely taper and square. The microstructure and microhardness of weld stir zone (WSZ) were examined and linked with the strength parameters of the joints. Adequate frictional heat generation from 20 mm shoulder diameter and pulsating stirring action of square pin revealed the formation of very fine grains in the weld nugget zone (WNZ). Due to enhanced material flow and the production of a defect-free stir zone, the joint created using a tool with a 20 mm shoulder diameter and square pin profile had the maximum hardness of 117 HV and the highest tensile strength of 284 MPa. The ductile mechanism of fracture is revealed by the presence of fine dimples accumulating in the tensile fractured surface of the joint fabricated by 20 mm tool shoulder diameter and square pin.

The impact of welding heat input on microstructure, micro-texture, and mechanical properties of stir zone in friction stir welded DP600 steel

In this research, the impact of the heat input (HI) used during friction stir welding (FSW) on the microstructure, micro-texture and mechanical properties of DP600 steel was examined. Two different sets of rotational and transverse speeds were utilized to produce robust welds, one with low HI and the other with high. The outcomes demonstrated that various products such as polygonal ferrite (PF), Widmanstatten ferrite (WF), ferrite-carbide aggregate (FCA), and bainite were created in the stir zone (SZ) during the FSW of DP600 steel. After microscopic analysis, it was found that the high HI weld exhibited a greater amount of WF and bainite, resulting in higher hardness and ultimate tensile strength values than the low HI weld. The low HI weld displayed texture components including D1, D2, and E, with a slight cube component. These components were thought to result from the transformation of a strong B texture component and a weaker R texture component of prior austenite, indicating continious dynamic recrystallization during the FSW process. On the other hand, the high HI sample had a strong cube texture component and a weaker D shear component, a result of the transformation of a strong R shear texture component of prior austenite, suggesting discountinious dynamic recrystallization during FSW. The study determined that the welding HI greatly influences the proportion of microconstituents, the development of micro-texture, and the mechanical characteristics of the SZ during the FSW of DP600 steel.

Microstructure, mechanical characteristics, and electrochemical behavior of the wide-area stir zone fabricated in Al5083 by friction stir processing with overlapping technique

In the current study, a wide-area stir region was created in Al5083 aluminum alloy using multi-pass friction stir processing (FSP) with 50% pin overlapping. Microstructural investigations such as grain structure analysis and intermetallic particle (IMPs) distribution were carried out on processed alloys using optical and scanning electron microscopy (SEM). Recrystallized fine grains were developed after FSP due to the intense plastic straining and dynamic recrystallization. It was also identified that the grain refinement was uniform in the stir region of all overlapping passes, resulting in uniform hardness over the wide-area stir region. Three different types of IMPs, such as needle shape iron-based IMPs, round shape magnesium-based IMPs, and the very fine magnesium-based IMPs along the grain boundaries, were identified from the SEM analysis. The tensile test findings showed that the elongation improved drastically after overlapping FSP, while the hardness and tensile strength were found to be decreased due to high temperature thermal cycles. Electrochemical investigations revealed that the corrosion rate decreased after FSP due to the formation of uniform grain structure and dissolution of iron-based IMPs.

In-Situ Al-Mg Alloy Base Composite Reinforced by Oxides and Intermetallic Compounds Resulted from Decomposition of ZrW2O8 during Multipass Friction Stir Processing.

In the presented work, the effect of friction stir processing admixing the zirconium tungstate ZrW2O8 powder on the microstructure, mechanical and tribological properties of the AA5056 Al-Mg alloy stir zone has been studied. The FSP resulted in obtaining dense composite stir zones where α-ZrW2O8 underwent the following changes: (i) high-temperature transformation into metastable β'-ZrW2O8 and (ii) decomposition into WO3 and ZrO2 oxides followed by the formation of intermetallic compounds WAl12 and ZrAl3. These precipitates served as reinforcing phases to improve mechanical and tribological characteristics of the obtained fine-grained composites. The reduced values of wear rate and friction coefficient are due to the combined action the Hall-Petch mechanism and reinforcement by the decomposition products, including Al2O3, ZrO2, β'-ZrW2O8 and intermetallic compounds such as WAl12 and ZrAl3. Potential applications of the above-discussed composites maybe related to their improved tribological characteristics, for example in aerospace and vehicle-building industries.

Fabrication of Aluminum 5083/SiC Surface Composite on Tungsten Inert Gas Weld Joint by Novel Direct Friction Stir Processing Technique

For the creation of surface reinforcement particles in the metal matrix, friction stir processing is frequently utilized. Formation of aluminum/SiC surface composite on Tungsten Inert Gas (TIG) butt weld of Al5083 by a novel technique of direct friction stir processing (DFSP) using a hollow tool is successfully demonstrated in this present work. Deposition of SiC in the stir zone of DFSP was confirmed by X-Ray diffraction (XRD) method. Micro analysis of weld joint was achieved using metallographic microscope and scanning electron microscope (SEM). Microstructure of stir zone of DFSP shows finely distributed SiC reinforcement particles in aluminum matrix. Absence of detrimental intermetallics was confirmed by energy dispersive spectroscopy (EDS) analysis. Tensile strength of DFSPed specimen was found to be 227.3 MPa which is 19.5% lower than UTS of autogenous TIG weld specimen. Microhardness of SZ of DFSP was found to be increased from TIG weld microhardness of 86 Hv to 107 Hv due to presence of SiC particles.

Mechanisms of abnormal grain growth in friction-stir-welded aluminum alloy 6061-T6

The relationship between the temperature conditions during friction-stir welding (FSW), the stir-zone microstructure, and the thermal stability of welded aluminum-alloy 6061 joints was established. To facilitate interpretation of the microstructural data, temperature distributions generated during FSW were quantified using a finite-element-modeling (FEM) approach. In all cases, the stir-zone microstructure was found to be unstable against abnormal grain growth (AGG) during post-weld solution annealing. Moreover, it was found that AGG always developed very rapidly, being nearly complete during heating of the welded material from ambient condition to the solution temperature. In all welded conditions, annealing behavior followed Humphrey's cellular-growth model. In particular, for low-heat-input conditions, a combination of a fine-grain structure and a low content of secondary particles gave rise to a competition between normal grain growth and AGG. As a result, the final grain size was relatively small. By contrast, high-heat-input conditions gave rise to a combination of relatively-coarse grains and a high fraction of particles in the weld nugget, which provided microstructural stability. However, a fine-grain surface layer associated with the tool shoulder triggered catastrophic grain coarsening that eventually consumed the entire weld zone and resulted in millimeter-scale grains. Remarkably, AGG led to a 40 o 〈111〉 rotation of the crystallographic texture in the stir zone. It was thus concluded that the AGG was governed by at least two mechanisms, viz., the pinning effect exerted by second-phase particles and the enhanced mobility of 40 o < 111 > boundaries. • Annealing behavior of FSW joints is critically influenced by the weld heat input. • Abnormal grain growth develops at the early stage of the post-weld heat treatment. • Abnormal grain growth is governed by two different mechanisms.

Realizing ultrafine grain structure of Cu-Cr-Zr alloy via friction stir welding / processing

40 mm thick coarse-grained (up to 10 – 20 mm) CuCrZr mold wall to 2 mm thick pure copper plate lap joint was performed using friction stir welding (FSW) operating a H13 die steel tool. The obtained defect-free joint indicates the potential of FSW to restore worn-out copper molds wall. FSW resulted in ultrafine microstructure (0.5 –1.0 µm) of stir zone strengthened by chromium and Cu5Zr nanoparticles. Grain boundary and dispersion hardening increase the hardness of the stir zone up to 150 –190 HV1 compared to 110 –130 HV1 of the initial coarse-grained structure. Based on the results, friction stir welding and related friction stir processing technologies are proposed as a severe plastic deformation method to obtain an ultrafine-grained state of CuCrZr alloys.

Strategized friction stir welded AA6061-T6/SiC composite lap joint suitable for sheet metal applications

Friction Stir Welding (FSW) is one of the best choices of joining light weight metal structures involving lap joints as conventional welding methods find difficult in getting sound weld joints. Aluminium alloys are lightweight materials relatively used in space frame structures, ship buildings and panels of automotive vehicles. Main objective of this research is to investigate Al–SiC FSW lap joints and to examine the suitable pre-fill nanoparticles in the configured grooves to augment the weld strength. Three different volume additions of SiC nanoparticles and tool rotational speed were considered to fabricate lap joints for the investigations. Tool rotational speed and volume of SiC reinforcement have a significant impact on the dissemination of SiC in the weldment and weld quality. The spread of SiC nanoparticles in the weld area strongly affects the weld microstructure and mechanical characteristics. Nano SiC filled lap joint has shown a significant improvement in mechanical properties as compared to a joint without nanoparticles. The best lap joint is achieved with 20 vol% of SiC and 1500 rpm of rotational speed. The investigations imply that the tensile strength is decreased for joints with 26 vol% of SiC, due to clustering of reinforcement particles. The supplement of SiC nanoparticles restricts the growth of grains and refines the stir zone (SZ) microstructure and hence this method of weld process is recommended for lap weld joints in metal structures.

A specific analytical study of friction stir welded Ti-6Al-4V grade 5 alloy: Stir zone microstructure and mechanical properties

The light metal titanium alloys find extensive usage is in industries where weight is a significant factor. Research in friction stir welding (FSW) aimed at producing strong joints without adding extra weight since machines like aircraft and automobiles must have as little weight as possible to improve their fly-to-buy ratio. This study reports 10 mm thick titanium alloy plates that are FSWed by varying rotational speed and tool traverse speed using the W-La2O3 tool. Due to the heat produced during the welding process, each material region experiences a different thermal cycle, which significantly affects microstructural changes. The peak temperature during FSW exceeded the β-transition temperature, causing phase transformations in the stir zone (SZ). A lamellar structure was observed in the SZ, and a transition line region (TLR), Bimodal, or duplex microstructure obtained consists of (α + β) phase. The SZ grain size decreases along the thickness direction, tensile strength increases, and reaches 89–102% of the base material. A lower hardness value is found in the SZ than in the base material (BM). The tensile fracture surface is observed to have a honeycomb-like structure or dimples, representing ductile fracture.

ВЛИЯНИЕ РЕЖИМА СВАРКИ ТРЕНИЕМ С ПЕРЕМЕШИВАНИЕМ НА ТЕРМИЧЕСКУЮ СТАБИЛЬНОСТЬ СПЛАВА АД33

Friction stir welding (FSW) is an innovative technology for the solid-phase joining of metal materials. It allows producing permanent joints of materials conventionally considered to be nonweldable, in particular aluminum alloys. However, an essential drawback of FSW is the relatively low stability of the stir zone microstructure. In particular, during post-weld heat treatment, seams frequently demonstrate abnormal grain growth. Such an undesirable phenomenon is often interpreted in terms of the so-called Humphrey’s cellular model, according to which the abnormal behavior is attributed to the essential microstructure refinement and the dissolution of the second-phase particles occurring during FSW. Since these two processes significantly depend on the temperature, the authors suggested that the thermal stability of the produced FSW seams should also be associated with the FSW heat conditions. To test this hypothesis, the authors obtained two welded seams at different FSW conditions and then studied their microstructural behavior during T6 mode thermal treatment (involving solution heat treatment followed by artificial aging). The authors used the advanced electron backscatter diffraction technique (EBSD) to investigate microstructure. In full accordance with the initial idea, the investigation showed that microstructural evolution in both studied microstructure states varied wildly. Specifically, the study identified that the reduction in the FSW temperature causes the suppression of abnormal grain growth. The authors suggested that the enhanced thermal stability of the material is associated with the conservation of the second-phase particles during the low-temperature FSW.

Numerical modeling and experimental investigation on the effect of rotation speed on microstructural evaluation and mechanical properties of copper during friction stir processing

In the present work, the effect of different parameters of friction stir processing (FSP) on microstructure and mechanical properties of pure copper were investigated numerically and experimentally. Three different tool rotation speed (900, 1200 and 1500 rpm) and a constant traverse speed (60 mm/min) were used as FSP parameters. To model the microstructure of stir zone (SZ) which undergos the dynamic recrystallization (DRX) and grain growth, Zener-Hollomom parameter were used to predict the grain size. In the first step the temperature distribution was formulated and solved by a commercial software COMSOL Multiphysics. An analytical model were then utilized to calculate the strain rate distribution in SZ using MATLAB. Finally, strain rate and temperature were imposed to Zener-Hollomon equation to predict the grain size. The results of modeling indicated that by increasing the rotation speed, the Z parameters decreased and subsequently the grain size increased. The predicted grain size were in a good agreement with the experimental results. The mechanical properties also improved by grain refinement.

Microstructural and Mechanical Behaviors of Friction Stir Welded Dissimilar AA6082‐AA7075 Joints

In this research, microstructural events and mechanical behaviors in dissimilar friction stir welding (FSW) of aluminium (Al) alloy AA6082‐AA7075 joints have been evaluated to apply aerospace, defense, and military sectors. FSW parametric effects have a more significant impact on the mechanical performances and microstructure of produced joints. FSW tool rotational speed, welding speed, and tool plunge speed were chosen to make the weld joints. The rotational tool speeds of 1600 rpm and 2300 rpm, welding speeds of 40 mm/min and 60 mm/min, and tool plunge speeds of 20 mm/min and 30 mm/min were set as the upper and lower limits. A constant axial force of 5 kN was maintained throughout the joint fabrication process. A taper pin‐profiled tool was utilized to produce the butt welded joints. Mechanical properties of microhardness, tensile strength, yield strength, elongation, and bending strength of the joints were analyzed. The response of the stir zone microstructure to processing parameters was evaluated using optical microscopy (OM) and fractographic analysis of a tensile specimen shown by scanning electron microscope (SEM). The weld joints produced at 2300 rpm, tool traveling rate of 40 mm/min, and tool plunge speed of 30 mm/min showed the greatest tensile strength of the 191 MPa hardness of 145 Hv at the weld center and also the maximum bending strength of 114.23 N/mm2 was achieved. The lowest bending strength of 25.38 N/mm2 was obtained at 1600 rpm with 60 mm/min due to inappropriate mixing of the base metals and poor joint quality. Furthermore, this study revealed that a higher tool plunge speed facilitates the formation of equiaxed grains in the thermomechanically affected zone (TMAZ) on the advancing side (AS). Additionally, the increment in tool rotational speed significantly improved the tensile strength, weld joint quality, and joint efficiency.

Corrosion Behavior and Microstructure of Stir Zone in Fe-30Mn-3Al-3Si Twinning-Induced Plasticity Steel after Friction Stir Welding

The effect of friction stir welding on microstructure and corrosion property was studied in Fe-30Mn-3Al-3Si (wt.%) twinning-induced plasticity steel using both an electron backscattered diffractometer and electrochemical testing (i.e., polarization test and electrochemical impedance spectroscope). The stir zone has a relatively higher corrosion resistance with uniform dissolution on the surface despite after welding, whereas the base metal shows localized corrosion attack with deep and long degradation along the grain boundaries. This is due to the corrosion-resistant coincidence site lattice boundaries caused by discontinuous dynamic recrystallization via the grain boundary bulging during the friction stir welding.

Strength, failure and microstructure development for friction stir welded AA6061-T6 joints with different tool pin profiles

The influence of seven different tool pin profiles was investigated to appraise the tensile, flexural strength, fracture behavior, and microstructure evolution in friction stir welded similar AA6061-T6 joints. Results indicate that each tool pin profile affects the material flow/intermixing in different ways; consequently, the weld nugget feature and grain size in the stir zone (SZ) were also observed to be different. Relatively finer grains with homogenous microstructure in SZ were observed for joints prepared using cylindrical grooved with straight flutes (CGF) and cylindrical grooved (CG) tool pins. The highest tensile strength and flexural load were observed for joints obtained with CGF tool pin followed by CG tool pin. A relationship between average yield strength of the joint and inverse square root of average SZ grain size was established for these joints. EBSD analysis revealed that the SZ is the mixture of low angle grain boundaries and high angle grain boundaries (HAGBs) and the fraction is controlled by different pin profiles. The HAGBs and high shear texture components B/B¯ and C were found predominant in welds prepared with CGF and CG tool pins. Fractographic analyses showed the presence of numerous dimples in sound bonded regions indicating the ductile fracture; however, tearing/rupture and shear failure were witnessed near the vicinity of the tunnel region.

Similar and dissimilar welds of ultrafine grained aluminium obtained by friction stir welding

Samples from commercially pure aluminium were subjected to various number of passes of Incremental Equal Channel Angular Pressing (I-ECAP) and subsequently welded using Friction Stir Welding (FSW). Similar and dissimilar welds were obtained and investigated in terms of their microstructure and mechanical properties. In the case of similar weld from coarse grained aluminium in the stir zone a decreased average grain size was obtained, which resulted in enhanced microhardness. In the case of samples after I-ECAP, the ultrafine grained regime has not been preserved, which caused a drop in microhardness in the stir zone. Nevertheless, obtained results were still higher than those for coarse grained sample. In all welds the average grain size of 2.1–3.7 μm was obtained. No correlation between the microstructure of base material and stir zone has been found. Tensile tests revealed, that the localization of deformation was obtained in each weld in the area of the biggest average grain size. For dissimilar welds from deformed and undeformed samples a gradient change in microstructure and microhardness was obtained on the cross-section of the welds.

The Effects of Pin Offset for FSW of Dissimilar Materials: A Study for AA 7075 – AA 6013

The trend in welding of dissimilar aluminum alloys oriented to new application techniques to increase the functionality and perform the welding procedure without any problem in the welded joints. The pin profile and process parameters determined for the friction stir welding greatly affect the weldability and strength of the welded joints. In addition, it is also considered that the pin offset is also an effective factor on the strength and microstructure of welded joints. In the present study, aluminum alloys AA 6013–T6 and AA 7075–T651 were welded with the FSW process applying pin offset technique. The changes in the mechanical and microstructural properties were investigated. The onion ring structure was observed in all of microstructure of weld stir zone. Except the welded joint fabricated with the tool rotational speed of 400 rpm for both without pin offset and with offset to retreating side, all the welded joints were fractured at the base metal region and heat affected zone in AA 6013 alloy. The welded joints fabricated with the tool rotational speed of 400 rpm consisted of small and large cavity-type defects. Although defects were found to occur in the welded joints, none of the welded joints were fractured at the SZ during the tensile and bending tests. The ultimate tensile strength and elongation at rupture of the dissimilar FS welded joints were ranged between 164 MPa and 179 MPa, 6.5 and 7.6%, respectively. These defects were found to affect the ductility feature of the welded joints. The pin offset direction was found to affect the volume of parent materials in the stir zone. Hence, the material volume in the onion rings changes and, the hardness distribution is also affected by the changes in the material volume. Keywords: aluminum alloys, friction stir welding parameters, fracture analysis

Effect of Tool Rotation Speed on Microstructure and Hardness of Friction-Stir-Welded 9Cr-1Mo Steel

In this study, friction stir welding (FSW) of 9Cr-1Mo steel was carried out with tungsten lanthanum oxide (W-La2O3) tool to study the influence of tool rotation speeds (200 rpm and 500 rpm) on microstructure and hardness. A smooth defect-free weld joint with complete penetration was accomplished by both rotational speeds. In stir zone (SZ), a fine and lath martensitic microstructure was explored for the 200 rpm and the 500 rpm welds, respectively. The tangible increment in the average hardness of both SZ and thermomechanical affected zone (TMAZ) compared to the base metal (stir zone/TMAZ: ~ 420 VHN, base metal: ~ 212 VHN) was observed due to the effect of phase transformation.