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Interplay of L1 2-(Al,Zn) 3Zr Dispersoids and η′ Precipitation in a Model Al-Zn-Mg-Cu-Zr Alloy

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Document pages: 31 pages

Abstract: Al3Zr dispersoids and their interaction with precipitates and base alloying elements have been investigated in an Al-Zn-Mg-Cu-Zr alloy. By combining atom probe tomography with aberration-corrected scanning transmission electron microscopy, we show that Zn can effectively stabilize dispersoids of L12 structure with (Al,Zn)3Zr type composition. These Zn-containing Al3Zr dispersoids accelerate the formation of η precipitates during aging. More specific, composite particles with a structure comprising a spherical (Al,Zn)3Zr core with ~25 nm in diameter, enveloped by plate-shaped η precipitates are uniformly distributed in the grain interior. At grain boundaries, irregular-shaped η precipitates with Mg(Zn,Al,Cu)2 type composition in coexistence with coarser 60 nm-sized (Al,Zn)3Zr dispersoids are observed, along with 10-nm wide precipitate-free zones adjacent to the dispersoid and perpendicular to the grain boundaries they are placed on. Our findings provide insights for devising inexpensive, Zn containing L12 dispersoids to strengthen Al-alloys for high-temperature applications, and explicitly provide a fundamental understanding on the formation mechanism of L12 structured composite dispersoids that coexist with η precipitates.

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