Restirring and Reheating Effects on Microstructural Evolution of Al–Zn–Mg–Cu Alloy during Underwater Friction Stir Additive Manufacturing

Abstract

Friction stir additive manufacturing (FSAM) can be potentially used for fabricating high-performance components owing to its advantages of solid-state processing. However, the inhomogeneous microstructures and mechanical properties of the build attributed to the complex process involving restirring and reheating deserve attention. This study is based on the previous research of the underwater FSAMed 7A04 aluminum alloy and adopts a quasi in situ experimental method, i.e., after each pass of the underwater FSAM, samples were taken from the build for microstructural observation to investigate the restirring and reheating effects on microstructural evolution during the underwater FSAM. Fine-grain microstructures were formed in the stir zone during the single-pass underwater FSAM. After restirring, the grain size at the bottom of the overlapping region decreased from 1.97 to 0.87 μm, the recrystallization degree reduced from 74.0% to 29.8%, and the initial random texture transformed into a strong shear texture composed of the C {110}<11¯0>. After reheating, static recrystallization occurred in the regions close to the new additive zones, increasing the grain size and recrystallization degree. This study not only revealed the microstructural evolution during the underwater FSAM but also provided a guideline for further optimization of the mechanical properties of the Al–Zn–Mg–Cu alloy build.

A Comprehensive Review of Friction Stir Additive Manufacturing (FSAM) of Non-Ferrous Alloys

“…Effect of re-stirring and re-heating (under water) on microstructure evolution for Al-Zn-Mg-Cu alloy (Al-7A04-T6) was well explored in a recent study [ 84 ]. Four plates were laminated, and the samples were subjected to electron backscatter diffraction (EBSD) for grain morphology investigation after each pass (first, second, and third).…”

“… Effect of re-stirring and re-heating on grain characteristics of Al-7A04-T6 build: ( A ) Stir zone and distributions of grain sizes; ( B ) Fraction of grain type (re-crystalized, sub-structured, and deformed). (reprinted from [ 84 ] permission not required). …”

The Influence of the Deposition Speed during Friction Screw Extrusion Additive Manufacturing of AA6060

“…Several solid-state additive manufacturing processes have emerged in recent years, including friction stir additive manufacturing (FSAM) [3], additive friction stir deposition (AFSD) [4], friction surfacing (FS) [5], and friction surface cladding (FSC) [6], among various additional techniques.…”