Abstract
Six-millimeter-thick 2A14 Al alloy plates were friction stir processed (FSP) with different initial precipitation states of as-cast, homogenization, rolling, and T6. The results indicated that FSP can dramatically reduce the grain and particle size and promote the formation of fine recrystallized grains with random orientation in the stirred zone (SZ). No significant influences of the initial precipitation states of base metal (BM) on the grain size, grain boundary characteristic, texture component, and texture intensity of SZ were perceived. Rather, the initial precipitation states can evidently affect the morphology and distribution of precipitates and dislocations. The dominant C and A1* texture components developed in the SZ are correlated with the shear deformation and dynamic recrystallization. And the weakened texture intensity created in the SZ after FSP also signifies that discontinuous dynamic recrystallization might be involved. Compared with the corresponding BM, the SZ fabricated by the BM under as-cast and homogenized states was strengthened arising from the obvious refined grains, uniform dispersed particles, and elimination of casting defects caused by FSP, while the softening of SZ was observed for the BM under rolled and T6 states, which are mainly dependent on the reduction of dislocation density and dissolution/coarsening of fine precipitates during FSP.
Highlights
The 2A14 aluminum alloy has potential for various high performance applications in the aerospace structural components, transport systems and defense equipment because of its high strength to weight ratio, excellent fracture toughness and corrosion resistance [1, 2]
Khaled J. et al [10] documented the evolution of microstructures and mechanical properties produced with multi-pass Friction stir processing (FSP) and concluded that all FSPed samples show a reduction in the tensile strength in comparison with the base metal (BM) sample due to the dissolution of fine precipitates and reduction of dislocation density
The main conclusions derived from the experimental results were as follows: (1) Performing FSP with air cooling were found to be beneficial for achieving fine equiaxed grain structures with a higher fraction of HAGBs in the range of 78.3% ~ 89.5% for the BM under as-cast, homogenized, rolled and T6 states
Summary
The 2A14 aluminum alloy has potential for various high performance applications in the aerospace structural components, transport systems and defense equipment because of its high strength to weight ratio, excellent fracture toughness and corrosion resistance [1, 2]. As a large plastic forming process, FSP provides an extensive prospect for refining the grain of aluminum alloys, which can in turn contribute to the enhancement of mechanical properties and other properties [4, 5] It has been proposed as a potential solid-state processing technique to modify microstructures, achieve superplasticity, and synthesize in-situ composites and intermetallic compounds [6, 7]. Vivek V. et al [8] studied the effect of polygonal pin profiles on the superplasticity of FSPed AA7075 alloy They suggested that evenly distributed hardness was found in the SZ on account of less pulsating actions and adequate material flow generated around the square pin. The results demonstrated that FSP with rapid cooling method can efficiently refine the grain structures and achieve enhanced mechanical properties
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