Friction Stir Welded Al Alloy Research Articles

Microstructure and Corrosion Behavior of Friction Stir Welded Al Alloy Coated by In Situ Shot-Peening-Assisted Cold Spray

To improve the corrosion resistance of friction stir welded (FSW) joints, in situ shot-peening-assisted cold spray coating was applied to the surface of FSW joints. The microstructure and corrosion behavior of the coatings were investigated. The results showed that a dense coating was obtained by cold spraying technology. Moreover, the use of in situ shot-peening-assisted technology significantly reduced the porosity of the coating, which has a positive impact on the microstructure and the mechanical performance. Exfoliation corrosion tests showed that the coating affected positively on the corrosion resistance. On the coated surface, the craters caused by shot-peening particles were corroded in the form of exfoliation corrosion, while the exposed particles were corroded in the form of intercrystalline corrosion. This work provides a new approach to the corrosion protection of FSW joints.

Metallurgical Characterization and Hardness Evaluation of Dissimilar Friction Stir Welded Al Alloy Flat Plates

Friction Stir Welding (FSW) is commonly developed for welding of metals of the same kind like aluminium copper, steel and titanium. However, FSW also has the potential to produce high-quality joints between dissimilar metals which are differ in physical and mechanical properties. In this work dissimilar aluminium alloys plates of AA 6101-T6 and AA 6351-T6 with 6 mm thick were friction stir butt welded under the influence of different process parameters. The influence of various parameters, particularly the rotational speed on microstructures and hardness properties of the joints has been addressed. The microstructure of weld joints has been studied using an optical microscope and distinct zones are also identified. Fine-equiaxed and refined grains are observed at nugget zone of dissimilar joints due to effective stirring action of cylindrical profile tool pin at higher tool rotational speeds. The intermetallic compounds that form in the joints has been examined by the X-ray diffraction (XRD) and the presence of intermetallic compound Mg2Si in base metals and FSW joints was detected. Therefore, it can be understood that the intermetallic compound affects the hardness of butt joints. The highest and lowest SZ hardness are obtained with the welds fabricated with 1300rpm, 60 m/min, 4kN and with 900 rpm, 60 mm/min and 8kN respectively.

On material flow in Friction Stir Welded Al alloys

AA6082-T6 joints were produced using a trigonal shape pin. The influence of Friction Stir Welding (FSW) process parameters on the formation of banded structures was predicted using numerical modeling and then experimentally validated by optical and electron microscopy. Special attention was paid to the formation and evolution of banded structures observed in the plane of the welded sheets. A finite element (FE) analysis based on the Coupled Eulerian–Lagrangian formulation was developed to predict and quantify the influence of FSW process parameters on the formation and extent of the banded structures. The combination of the experimental and numerical analyses showed that the formation of the banded structures is mainly related to the geometry of the pin whereas the friction conditions have a much smaller effect.

Banded structures in friction stir welded Al alloys

In the friction stir welding (FSW) process, onion rings are the result of the periodical deposition of layers of material which have a determining effect on the mechanical properties of FSW joints. The extent and characteristics of the onion rings are quantified in the present study and related to FSW processing parameters. A comprehensive analysis of the steady state model proposed by Jacquin et al. is carried out and an approach is proposed to extend the model for the prediction of onion rings during welding of 6082-T6 aluminum alloy. The model's setting and computation method, based on the SU/PG method, are described and compared to the results of experimental microstructural investigations. The outputs are flow patterns, strain rate and temperature contours, depending on the tool kinematics, the constitutive equation of the material and the friction coefficient at the interface tool/material. The microstructure evolution in the weld is related to the model results, and especially the evolution of banded structure and void defects.

Effects of tool rotational and welding speed on microstructure and mechanical properties of bobbin-tool friction-stir welded Mg AZ31

The effects of rotational and welding speeds on the microstructure and mechanical properties of bobbin-tool friction stir welded (BT-FSW) Mg AZ31 were investigated. The results indicated that the thermo-mechanically affected zone (TMAZ) consisted of equiaxed grains, which were inconsistent with the deformed, rotated and elongated grains found in the TMAZs of bobbin-tool friction stir welded Al alloys and friction stir welded Al and Mg alloys. The average grain size increased as the ratio of the rotational speed to welding speed increased. Excellent welds with no degradation in hardness were produced using a low heat input. Mechanical tests revealed that the ultimate tensile strengths gradually increased with increasing welding speed while keeping the rotational speed constant. The rotational and welding speeds had only slight influences on the yield stress and fracture elongation.

Formability and microstructural stability of friction stir welded Al alloy tube during subsequent spinning and post weld heat treatment

Subsequent spinning combined with post weld heat treatment (PWHT) was imposed to the friction-stir welding tube, and the effects of PWHT on the formability and microstructural stability of the FSW tubes were investigated in detail. The formability of tubes, evaluated by the hydraulic bulge test, is significantly improved after spinning and PWHT due to the grain refinement, removal of the thickness reduction and heterogeneous microstructure of the weld. Even abnormal grain growth occurs, the tubes still show a relatively high formability compared to the extruded tubes. The PWHT process plays key roles in controlling the size of precipitates and subgrains, and consequently dominates the microstructure stability that is correlated to the strain hardenability and formability of the tubes.

Experimental Estimation of Strain Rate during FSW of Al-Alloy Using Plane-Strain Compression

Friction stir welding (FSW) makes the stir zone with fine recrystallized grain structure. The recrystallized grains would be formed through dynamic recrystallization at high temperatures and high strain-rate. The present study experimentally simulated the dynamically recrystallized microstructure of a friction stir welded Al alloy 1050 produced at 600 rpm rotation and 100 mm/min travel speed, using combination of the plane-strain compression at various strain rates and the subsequent cooling along the cooling cycle of FSW. The equiaxed grain structures similar to the microstructure of the stir zone were produced at strain rates between 0.1 and 32 s-1; the grain size decreased with increasing strain rate. Strain rate during the FSW could be estimated to be about 1.8 s-1. The present study suggests that plane-strain compression test can simulate the recrystallized grain structure of the friction stir welds.

Mechanical properties of friction stir welded Al alloys with different hardening mechanisms

The mechanical properties of precipitation hardened Al 6061-T651 and Al 7075-T6 and strain hardened Al 5083-H32, friction stir welded with various welding parameters, were examined in the present study. 4 mm thick Al 6061-T651, Al 7075-T6, and Al 5083-H32 alloy plates were used for friction stir welding (FSW) with rotating speed varied from 1000 to 2500 rpm (rotation per minute) and welding speed ranging from 0.1 to 0.4 mpm (m/min). Each alloy displayed slightly different trends with respect to the effect of different welding parameters on the tensile properties of the FSWed Al alloys. The tensile elongation of FSWed Al 6061-T651 and Al 7075-T6 tended to increase greatly, while the tensile strength decreased marginally, with increasing welding speed and/or decreasing rotating speed. The tensile strength and the tensile elongation of Al 6061-T651 decreased from 135 to 154 MPa and 10.6 to 17.0%, respectively, with increasing welding speed from 0.1 to 0.4 mpm at a rotating speed of 1,600 rpm. Unlike the age-hardened Al 6061-T651 and Al 7075-T6, the strain-hardened Al 5083-H32 showed no notable change in tensile property with varying welding parameters. The change in the strength level with different welding parameters for each alloy was not as significant as the variation in tensile elongation. It was believed that the tensile elongation of FSWed Al alloys with varying welding parameters was mainly determined by the coarse particle clustering. With respect to the change in tensile strength during friction stir welding, it is hypothesized that two competing mechanisms, recovery by friction and heat and strain hardening by plastic flow in the weld zone offset the effects of different welding parameters on the tensile strength level of FSWed Al alloys.

Post-weld formability of friction stir welded Al alloy 5052

Friction stir (FS) welds in Al alloys could be used as tailor welded blanks in automotive industry. Tailor welded blanks must exhibit adequate formability similar to that of the base material sheet. To evaluate the formability of FS welds in Al alloys for car body applications, a relationship between the fracture limit strain of plane strain deformation and the microstructure was examined in a FS welded thin Al alloy 5052 sheet. The fracture limit strain of plane strain deformation increased with increasing subgrain size in the stir zone. The present study suggests that the excellent fracture limit strain is attributed to the microstructure having both large grain size and a low density of dislocations and sub-boundaries in the stir zone of Al alloy 5052.

FIB-assisted TEM study of an oxide array in the root of a friction stir welded aluminium alloy

A local region in the preferentially etched line at the root part of a friction stir welded Al alloy was directly observed by TEM. TEM clarified that the preferentially etched line consisted of zigzag region having a high density of amorphous Al 2O 3 particles which originated from the initial butt surface oxide layer.

Relationship between mechanical properties and microstructure in friction stir welded Al alloys

Relationship between mechanical properties and microstructure in friction stir welded Al alloys

Relationship between mechanical properties and microstructure in friction stir welded Al alloys

Relationship between mechanical properties and microstructure in friction stir welded Al alloys

Ａｌ合金ＦＳＷ部の機械的特性とミクロ組織

Ａｌ合金ＦＳＷ部の機械的特性とミクロ組織

Microstructural and Mechanical Characterization of a Friction Stir Welded Al-Alloy

The microstructure and mechanical properties of a friction stir welded 6013 aluminum alloy have been investigated. A combination of optical and transmission electron microscopy was used to characterize the microstructure of the weld, the heat affected zone and the base material. Friction stir welding causes dynamic recrystallization in the weld resulting in smaller and equiaxed grains as compared to the larger elongated grains of the base material. The grain size of the heat-affected zone is retained. The strengthening precipitates in the weld are dissolved while those in the heat affected zone coarsened considerably. Mechanical properties were characterized using microhardness measurements and tensile tests. Microhardness profiles show that the heat-affected zone is the softest region. Tensile tests transverse to the weld revealed that the strength of the weld is reduced and that fracture takes place in the heat affected zone.