Effects of Heat Dissipation from Friction Stir Welding to Microstructures of Semi-Solid Cast 6063 Al Alloy

In this work, temperature distribution in semi-solid cast 6063 aluminum alloy workpieces during friction stir welding (FSW) was determined by finite element analysis (FEA). The FEA results were validated by comparing them with the measurement results from thermocouples. The maximum temperature of 534.2oC was predicted at the workpiece surface contacted with the tool shoulder. The temperature profiles obtained from FEA were used to explain microstructural changes during FSW. It was observed that relatively high temperature made α-Al grains became elongated and Mg2Si intermatalics turned into a rod-like morphology with round edges.

On the problem of tool destruction when obtaining fixed joints of thick-walled aluminum alloy blanks by friction welding with mixing

Introduction. Among the technologies for manufacturing rocket and aircraft bodies, marine vessels, and vehicles, currently, more and more attention is paid to the technology of friction stir welding (FSW). First of all, the use of this technology is necessary where it is required to produce fixed joints of high-strength aluminum alloys. In this case, special attention should be paid to welding thick-walled blanks, as fixed joints with a thickness of 30.0 mm or more are the target products in the rocket-space and aviation industries. At the same time, it is most prone to the formation of defects due to uneven heat distribution throughout the height of the blank. It can lead to a violation of the adhesive interaction between the weld metal and the tool and can even lead to a destruction of the welding tool. The purpose of this work is to reveal regularities of welding tool destruction depending on parameters of friction stir welding process of aluminum alloy AA5056 fixed joints with a thickness of 35.0 mm. Following research methods were used in the work: the obtaining of fixed joints was carried out by friction welding with mixing, the production of samples for research was carried out by electric erosion cutting, the study of samples was carried out using optical metallography methods. Results and discussion. As a result of performed studies, it is revealed that samples of aluminum alloy with a thickness of 35.0 mm have a heterogeneous structure through the height of weld. There are the tool shoulder effect zone and the pin effect zone, in which certain whirling of weld material caused by the presence of grooves on tool surface is distinctly distinguished. It is shown that the zone of shoulders effect is the most exposed to the formation of tunnel-type defects because of low loading force and high welding speeds. It is revealed that tool destruction occurs tangentially to the surface of the tool grooves due to the high tool load and high welding speeds.

Al Alloy Tailor welded Blanks Fabrication via Friction Stir Welding: Effect of Shoulder Size

Material flow and heat generation by tool shoulder during Friction Stir Welding (FSW) significantly alters the microstructural and thermomechanical behaviour of joints. The effect of shoulder size on mechanical properties of joints has not yet been reported in the FSW of Tailor Welded Blanks (TWBs). This article reports the effect of shoulder size on joint quality in FSW of TWBs between 6.35 mm thick plates of AA2024-T3 and 2.5 mm thick plates of AA7475-T7 alloys in butt joint configuration fabricated under shoulder sizes: 18 mm, 20 mm, and 22 mm. Microstructural evaluation of FSWed joints reveals a significant increase in grain size with shoulder diameter sizes. The X-ray EDS elemental maps reveal the presence of fine second phase particles stir zone. The progressive elimination of void defect with the increase in shoulder size was observed. The tensile testing reveals the highest strength of joints fabricated under shoulder size of 18 mm. Fractographic analyses of broken tensile specimens showed the mixed mode of failure in all the weld specimens.

Parameters Optimization of Dissimilar Friction Stir Welding for AA7079 and AA8050 through RSM

Aluminium alloy is widely used in engineering application, and it can be classified based on the constituent elements or alloying elements. Aluminium alloy is preferred for the nature of its tensile strength, ductility, and corrosion resistance in this research to make a dissimilar friction stir welding joint of aluminium alloys 7079 and 8050 materials. The tensile strength of the weld joint is estimated by the influence of the response surface methodology approach. The welding is carried out by preferred process parameters with a tool speed of 1000–2500 rpm, tool pin diameter of 2–6 mm, welding speed of 50–300 mm/min, and tool shoulder diameter of 10–20 mm. The ANOVA analysis and the prediction of tensile strength were conducted efficiently. From the RSM analysis, the tool pin diameter mostly modified the output of the result.

Enhancement of the Al/Mg Dissimilar Friction Stir Welding Joint Strength with the Assistance of Ultrasonic Vibration

The assistance of ultrasonic vibration during the friction stir welding (FSW) process has been verified as an effective approach for the improvement of joint strength. In the present study, experimentation on Al/Mg dissimilar alloys in butt joint configuration is implemented by employing FSW with and without the assistance of ultrasonic vibration. An optimized tool shoulder diameter of 12 mm is utilized, and the ultrasonic vibration is applied perpendicularly onto the tool along the welding direction, which is named UVaFSW. The results of joint appearance and macrostructure, characteristics of the intermetallic compounds (IMCs), as well as joint strength and fracture appearance are compared between Al/Mg FSW joints with and without ultrasonic vibration. It is demonstrated that the material intermixing between Al and Mg alloys is substantially strengthened in the UVaFSW joint compared with that in the FSW joint. Additionally, the ultrasonic vibration can be beneficial for the reduction of IMC thickness, as well as the formation of intermittently distributed IMC phases at the Al–Mg bonding interface. Consequently, the mechanical properties of Al/Mg FSW joints are significantly improved with the assistance of ultrasonic vibration. The maximum ultimate tensile strength is 206 MPa at tool rotation speed of 800 rpm and welding speed of 50 mm/min for the Al/Mg UVaFSW joint.

Residual Stresses Determination near FSW Joints by Combining the Hole Drilling Method and Reflection Hologram Interferometry

The results of residual stress characterization near friction stir welded (FSW) butt joint of aluminum plates are reported. The experimental analysis employs two-side measurements of local deformation response on small hole drilling by reflection hologram interferometry. The approach developed is based on the unequivocally solution of the properly posed inverse problem thus deriving both membrane and bending residual stress components. Residual stress components of high level are derived inside the tool shoulder borders on both specimen faces.

Effect of tool diameter ratio on the microstructural characteristics of a solid-state processed aluminum based metal matrix composite

Stir cast aluminum based metal matrix composites (MMCs) with silicon carbide (SiC) reinforcement particles consist of cast product dendrites and large agglomerated reinforcements. The agglomeration of SiC particles creates a difference in properties in the composite system. Friction stir processing (FSP) is used to overcome the uneven distribution of SiC particles in the aluminum matrix. The friction stir processed (FSPed) microstructure is significantly influenced by the process parameters used for processing. In FSP, the effect of the tool diameter ratio (tool shoulder diameter to pin diameter) on material flow, material mixing, material consolidation is more predominant than other parameters. Hence, a perfect combination of shoulder diameter to pin diameter is required to produce sufficient material flow. In this investigation, the tool diameter ratio is varied from 2.0 to 4.0 for processing composite material and thus FSPed zones were subjected to micro structural characterization. It was concluded that a tool diameter ratio of 3.0 yielded a defect free stir zone with higher hardness compared to other ratios.

Influence of Tool Runout on Force Measurement During Internal Void Monitoring for Friction Stir Welding of 6061-T6 Aluminum

The goal of this research was to examine how altering the amount of friction stir tool eccentricity while controlling the amount of slant in the tool shoulder (drivers of oscillatory process forces) effects the generation of process force transients during sub-surface void interaction. The knowledge gained will help improve the accuracy of force-based void monitoring methods that have the potential to reduce the need for post-weld inspection. Process force transients during sub-surface void formation were examined for multiple tools with varying magnitudes of kinematic runout. The eccentric motion of the tool produced oscillations in the process forces at the tools rotational frequency that became distorted when features (flats) on the tool probe interacted with voided volumes, generating an amplitude in the force signals at three times the tool rotational frequency (for three flat tools). A larger tool eccentricity generates a larger amplitude in the force signals at the tool’s rotational frequency that holds a larger potential to create a distortion during void interaction. It was determined that once void becomes large enough to produce an interaction that generates an amplitude at the third harmonic larger than 30% of the amplitude at the rotational frequency in a weld with no interaction (amplitude solely at rotational frequency), the trailing edge of the tool shoulder cannot fully consolidate the void, i.e., it will remain in the final weld. Additionally, once the void exceeds a certain size, the amplitudes of the third harmonics saturate at 70% of the amplitude at the rotational frequency during full consolidation. The interaction between the eccentric probe and sub-surface void was isolated by ensuring any geometric imperfection in the shoulder (slant) with respect to the rotational axis was removed. The results suggest that geometric imperfections (eccentricity and slant) with respect to the tool’s rotational axis must be known when developing a void monitoring method from force transients of this nature.

Influence of Tool Runout on Force Measurement during Internal Void Monitoring for Friction Stir Welding of 6061-T6 Aluminum

The goal of this research is to examine how altering the amount of friction stir tool eccentricity while controlling the amount of slant in the tool shoulder (drivers of oscillatory process forces) effects the generation of process force transients during sub-surface void interaction. The knowledge gained will help improve the accuracy of force-based void monitoring methods that have the potential to reduce the need for post-weld inspection. The eccentric motion of the tool produces oscillations in the process forces at the tool's rotational frequency, which becomes distorted when features on the probe interact with voids, generating an amplitude in the force signals at three times the tool rotational frequency (for three flat tools). A larger tool eccentricity generates a larger amplitude in the force signals at the tool's rotational frequency, which has a greater potential to create a distortion during void interaction. Once a void becomes large enough to produce amplitude at the third harmonic larger than 30% of the amplitude at the rotational frequency, the trailing edge of the tool shoulder cannot fully consolidate the void. The interaction between the eccentric probe and sub-surface void is isolated by ensuring any geometric imperfection in the shoulder (slant) is removed. The results suggest that geometric imperfections (eccentricity and slant) with respect to the tool's rotational axis must be known when developing a void monitoring method from force transients of this nature.

Study of the performance parameters of friction stir welded magnesium AZ31B alloy at optimized process parameters

The present study is aimed to analyze the effect of process parameters on the qualities of the Friction Stir Welded AZ31B Mg Alloy. Response Surface Methodology based Grey Relation Analysis technique was used to multi-optimization of the response parameters such as tensile strength (TS), percentage elongation (El), microhardness (MH), and impact strength (IMP). The mathematical models for response parameters were developed by considering tool rotational speed (RS), tool shoulder diameter (SD), and welding speed (WS) as process parameters. ANOVA (Analysis of Variance) was performed to check the adequacy of the formulated mathematical model and figure out the significant parameters. The results revealed that RS of 950 rpm, WS of 150 mm/min, and SD of 11 mm are the optimal process parameters for optimum response parameters (TS of 157.8700 MPa, IMP of 4.3001 Joule, MH of 84.1335 Hv, and El of 10.0071%). WS is the most significant factor, followed by RS and SD. The grain growth was observed in thermo-mechanically affected zone (TMAZ). The fracture analysis indicated that crack had initiated from the bottom of the centerline in the welded zone and propagated towards the advancing side.