The Metallurgy of High Fracture Toughness Aluminum-Based Plate Products for Aircraft Internal Structure

Tuning homogenization of high-strength aluminum alloys through thermodynamic alloying approach

“…However, completely eliminating the coarse phases (i.e., S phase) after high-temperature treatment for the alloys with narrow (such as alloy 2-2) or no a-Al single phase field (such as alloys 1-2 and 3-3) is still difficult. And the high solvus of the S phase will increase the quenching sensitivity and subsequently affect the strength, toughness, and SCC performance [4,5]. Therefore, a reasonable composition design should follow the basic principle [4] of low S phase solvus and wide a-Al single phase field, and those with narrow or no a-Al single phase field and high S phase solvus should be avoided [6,13,74].…”

“…And the high solvus of the S phase will increase the quenching sensitivity and subsequently affect the strength, toughness, and SCC performance [4,5]. Therefore, a reasonable composition design should follow the basic principle [4] of low S phase solvus and wide a-Al single phase field, and those with narrow or no a-Al single phase field and high S phase solvus should be avoided [6,13,74].…”

“…For the (Cu + Mg) content higher than this critical value or the alloys in (a-Al + S) phase field (i.e., the alloys 2-2, 1-2 and 3-3), there are still some residual coarse phases after hightemperature treatment (i.e., 475 °C) when the alloys lie outside the solubility limit at 490 °C (i.e., the alloys 1-2 and 3-3). However, these coarse phases can be completely dissolved after specific treatments (i.e., the two-step high-temperature treatment) when the alloys lie between the solubility limits at 475 °C and 490 °C (i.e., the alloy 2-2), but they may exhibit high quenching sensitivity [4,13,14]. Also, the Zn:Mg ratio can affect the fraction of the S phase, i.e., as the Zn:Mg ratio increases at a constant Cu content, the alloy will move from the two-phase field into a single-phase field [43]; high Zn:Mg ratio may increase the Cu solubility and more S phase can be dissolved [14], i.e., the AA7050 alloy.…”

“…15(c)), which will facilitate the dissolution of coarse phases and decrease the quenching sensitivity (without considering the effects of dispersoids), i.e., AA7056 alloy. Furthermore, the solvus of the coarse phase will increase along with narrowed a-Al single phase field for the (C Mg + C Cu ) > (3.5-3.8 wt%), which means that the fraction of the coarse phase will increase and is difficult to decrease even at high temperatures, and the quenching sensitivity will be intensified [4,5] (i.e., AA7136 alloy).…”

“…The high-strength aluminum alloys, e.g. AA7075, AA7050, AA7055, AA7085, are commonly applied in the transportation industry [1][2][3] with long-term objective of better integrated properties such as high strength and fracture toughness, good corrosion resistance and high fatigue resistance [4][5][6][7][8][9][10][11][12][13][14][15]. These properties are highly impacted by the strengthening precipitates, dispersoids and coarse constituents, i. e., insoluble Cu-/Fe-rich intermetallics and the partially soluble S (Al 2 CuMg) phase [7][8][9], as well as serious macro-/micro-segregation [12][13][14][15][16], all of which highly depend on the composition and processing [17][18][19][20][21][22][23][24][25][26][27][28][29][30].…”