Underwater dissimilar friction stir welding of aluminum alloys: Elucidating the grain size and hardness of the joints

Abstract

Underwater dissimilar friction stir welding of the AA6061 and AA7075 aluminum alloys was performed in this study. The effect of friction stir welding parameters on the grain size and hardness of the joints was studied using empirical models. The microstructure of the joints was characterized by means of light and transmission electron microscopes. The Vickers hardness test was conducted to measure the hardness of the joints. In addition, the process parameters including traverse and rotational speeds, grain size and hardness of the joints were correlated. The results revealed that the developed models predicted the hardness and grain size of the joints, precisely. Higher traverse speed and lower rotational speeds resulted in finer grain size and larger hardness. The grain boundaries and dislocations were identified as responsible for the higher hardness of the joints welded at lower heat input conditions. Moreover, the Hall–Petch relationship showed a deviation from its linear classical equation, which was due to the formation of substructures such as dislocations inside the grains.

Optimization of microstructural and mechanical properties of brass wire produced by friction stir extrusion using Taguchi method

“…Additionally, the sample periphery, as discussed before, experiences a higher cooling rate; therefore, it will contain a higher amount of dislocation density which can increase the microhardness value. 23–25…”

Friction stir butt-lap welding of A7N01P-T4 aluminum alloy: Efforts to mitigate defects and the resultant mechanical properties

“…Therefore, it is considered to be a convenient welding technology for preparation of aluminum alloy vehicle body, which has been proved to be appropriate for the butt welding of aluminum alloys. [15][16][17][18] However, in the friction stir lap welding (FSLW), the original lap surface will be influenced under the action of the welding tool, resulting in both a hookshaped defect (extending to the thermo-mechanical affected zone of the joint) at the advancing side (AS hook), and at the retreating side (RS hook, extending to nugget zone (NZ) of the joint). [19][20][21] Compared with the RS hook, AS hook has a more adverse effect on the performance of the joint because of a relatively severer interface migration.…”

“…Therefore, it is considered to be a convenient welding technology for preparation of aluminum alloy vehicle body, which has been proved to be appropriate for the butt welding of aluminum alloys. 15–18…”

A simulation-based study on the effect of underwater friction stir welding process parameters using different evolutionary optimization algorithms

“…In the past, researchers have optimized different FSW/UFSW process parameters using different modeling and optimization techniques for improving the mechanical properties of the joints. 12–17 Zhang et al. 13 optimized different UFSW parameters using response surface methodology (RSM) and analyzed that both extremely high and low rotational speed is harmful to the joints causing extreme thermal cycles and inadequate mixing of the material, respectively, leading to defects in AA 2219.…”

“…15 They further verified the results with experimental data published in the literature. The optimization of various process parameters using fractional design space was carried out by Bijanrostami and Vatankhah Barenji 16 during UFSW of AA 6061 and AA 7075. The developed empirical models precisely predicted the grain size and hardness of the welds.…”