A comparison of crystallographic texture and grain structure development in aluminum generated by friction stir welding and high strain torsion

The weight reduction concept is most effective to reduce the emissions of greenhouse gases from vehicles, which also improves fuel efficiency. Amongst lightweight materials, magnesium alloys are attractive to the automotive sector as a structural material. Welding feasibility of magnesium alloys acts as an influential role in its usage for lightweight prospects. Friction stir welding (FSW) is an appropriate technique as compared to other welding techniques to join magnesium alloys. Field of friction stir welding is emerging in the current scenario. The friction stir welding technique has been selected to weld AZ91 magnesium alloys in the current research work. The microstructure and mechanical characteristics of the produced FSW butt joints have been investigated. Further, the influence of post welding heat treatment (at 260 °C for 1 h) on these properties has also been examined. Post welding heat treatment (PWHT) resulted in the improvement of the grain structure of weld zones which affected the mechanical performance of the joints. After heat treatment, the tensile strength and elongation of the joint increased by 12.6 % and 31.9 % respectively. It is proven that after PWHT, the microhardness of the stir zone reduced and a comparatively smoothened microhardness profile of the FSW joint obtained. No considerable variation in the location of the tensile fracture was witnessed after PWHT. The results show that the impact toughness of the weld joints further decreases after post welding heat treatment.

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Microstructural Evolutions of 2N Grade Pure Al and 4N Grade High-Purity Al during Friction Stir Welding

Materials ◽

10.3390/ma14133606 ◽

2021 ◽

Vol 14 (13) ◽

pp. 3606

Author(s):

Tomoya Nagira ◽

Xiaochao Liu ◽

Kohasaku Ushioda ◽

Hidetoshi Fujii

Keyword(s):

Friction Stir Welding ◽

Dynamic Recrystallization ◽

Grain Refinement ◽

High Purity ◽

Cube Texture ◽

Grain Structure ◽

Welding Temperature ◽

Friction Stir ◽

Continuous Dynamic Recrystallization ◽

Dislocation Annihilation

The grain refinement mechanisms along the material flow path in pure and high-purity Al were examined, using the marker insert and tool stop action methods, during the rapid cooling friction stir welding using liquid CO2. In pure Al subjected to a low welding temperature of 0.56Tm (Tm: melting point), the resultant microstructure consisted of a mixture of equiaxed and elongated grains, including the subgrains. Discontinuous dynamic recrystallization (DDRX), continuous dynamic recrystallization (CDRX), and geometric dynamic recrystallization are the potential mechanisms of grain refinement. Increasing the welding temperature and Al purity encouraged dynamic recovery, including dislocation annihilation and rearrangement into subgrains, leading to the acceleration of CDRX and inhibition of DDRX. Both C- and B/-type shear textures were developed in microstructures consisting of equiaxed and elongated grains. In addition, DDRX via high-angle boundary bulging resulted in the development of the 45° rotated cube texture. The B/ shear texture was strengthened for the fine microstructure, where equiaxed recrystallized grains were fully developed through CDRX. In these cases, the texture is closely related to grain structure development.

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Grain Structure Formation Ahead of Tool during Friction Stir Welding of AZ31 Magnesium Alloy

Solid State Phenomena ◽

10.4028/www.scientific.net/ssp.160.313 ◽

2010 ◽

Vol 160 ◽

pp. 313-318 ◽

Cited By ~ 4

Author(s):

Uceu Suhuddin ◽

Sergey Mironov ◽

H. Takahashi ◽

Yutaka S. Sato ◽

Hiroyuki Kokawa ◽

...

Keyword(s):

Friction Stir Welding ◽

Magnesium Alloy ◽

Structure Formation ◽

Material Flow ◽

Boundary Migration ◽

Deformation Mode ◽

Grain Structure ◽

Az31 Magnesium Alloy ◽

Structure Evolution ◽

Friction Stir

The “stop-action” technique was employed to study grain structure evolution during friction-stir welding of AZ31 magnesium alloy. The grain structure formation was found to be mainly governed by the combination of the continuous and discontinuous recrystallization but also involved geometric effect of strain and local grain boundary migration. Orientation measurements showed that the deformation mode was very close to the simple shear associated with the rotating pin and material flow arose mainly from basal slip.

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