Abstract
The present work examined the effect of artificial aging on the microstructure, texture, and hardness homogeneity in aluminum alloy AA6082 subjected to friction stir processing (FSP). Aging was applied to FSP samples at three different temperatures (150 °C, 175 °C, and 200 °C) for a period of 1 h, 6 h, and 12 h. Microstructure analysis using optical Microscopy (OM) and Electron Back-Scattered Diffraction (EBSD) indicated that FSP produced fine equiaxed grains, with an average grain size of 6.5 μm, in the stir zone (SZ) due to dynamic recrystallization. Aging was shown to result in additional grain refinement in the SZ due to the occurrence of recovery and recrystallization with either increasing aging temperature and/or aging time. An optimum average grain size of 3–4 μm was obtained in the SZ by applying aging at 175 °C. This was accompanied by an increase in the fraction of high-angle grain boundaries. FSP provided a simple shear texture with a major component of B fiber. Increasing aging temperature and/or time resulted in the formation of recrystallization texture of a Cube orientation. In addition, Vickers microhardness was evaluated for the FSP sample, indicating a softening in the SZ due to the dissolution of the hardening precipitates. Compared to other aging temperatures, aging at 175 °C resulted in maximum hardness recovery (90 Hv) to the initial value of base metal (92.5 Hv). The hardness recovery is most likely attributed to the uniform distribution of fine hardening precipitates in the SZ when increasing the aging time to 12 h.
Highlights
Friction stir processing (FSP) has been used in the last two decades as an effective surface modification method for grain refinement in metals, for aluminum alloys [1,2]
The aforementioned studies indicated that post artificial aging is essential to acquiring a sufficient strength and hardness in the weld/stir zone of 6000 series aluminum alloys subjected to friction stir welding (FSW)/FSP, whenever a high loading condition is imposed
B fiber isis moderately partially preserved in the stir zone (SZ), while the precipitates during aging was effective in hindering lattice rotation and limiting the grain growth formation of hardening precipitates during aging was effective in hindering lattice rotation and recrystallization texture of the Cube orientation is moderately formed
Summary
Friction stir processing (FSP) has been used in the last two decades as an effective surface modification method for grain refinement in metals, for aluminum alloys [1,2]. Examined the effect of post-weld heat treatment (PWHT) on FSW of AA6056 and reported a considerable increase in strength of the weld zone due to the formation of a high density of fine Mg2 Si precipitates. The aforementioned studies indicated that post artificial aging is essential to acquiring a sufficient strength and hardness in the weld/stir zone of 6000 series aluminum alloys subjected to FSW/FSP, whenever a high loading condition is imposed. For such heat-treatable aluminum alloys, the temperature and period of the artificial aging play a significant role in the re-formation of β”. The hardness in the SZ was evaluated using Vickers microhardness tests
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