[delta] precipitation in an Al-Li-Cu-Mg-Zr alloy

Journal Article · Sun May 15 04:00:00 EDT 1994 · Scripta Metallurgica et Materialia; (United States)

DOI:https://doi.org/10.1016/0956-716X(94)90262-3· OSTI ID:7236606

Prasad, K S; Mukhopadhyay, A K; Gokhale, A A; Banerjee, D ^[1]; Goel, D B ^[2]

---

1. Defense Metallurgical Research Lab., Hyderabad (India)
2. Defense Metallurgical Research Lab., Hyderabad (India) Univ. of Roorkee (India). Dept. of Metallurgical Engineering

AlLi based [delta] phase has an NaTl structure (i.e., a diamond cubic) with a = 0.637nm and is an equilibrium phase in the binary Al-Li system. In heat treated binary Al-Li alloys of appropriate compositions, [delta] phase can format grain boundaries as well as within the grains. In commercially heat treated Al-Li-Cu alloys of 2090 specification, the grain boundary precipitate [delta] of the binary Al-Li system is replaced by a combination of T[sub 2](Al[sub 6]CuLi[sub 3]), R(Al[sub 5]CuLi[sub 3]) and T[sub 1](Al[sub 2]CuLi) phases. In similarly treated Al-Li-Cu-Mg alloys of 8090 specification, the copper rich T[sub 2] phase, present in the form of Al[sub 6]CuLi[sub 3[minus]x]Mg[sub x], is known to be the major coarse g.b. precipitate. The presence of an Al-Li-Cu-Mg based C phase at the grain boundaries of the commercially heat treated 8090 alloys has also been documented. No detailed study has yet been carried out to verify whether the [delta] phase can be present at the grain boundaries of the commercially heat treated 8090 alloys. Given the correlations between the g.b. phase morphology, g.b. phase chemistry, and the stress corrosion cracking resistance of these alloys, it is important that the g.b. precipitates be examined and identified. In this paper results using TEM are presented to show that the [delta] phase can be present in varying amounts at the grain boundaries in an 8090 alloy when heat treated in the temperature range of 170--350 C. An examination is also made of the [delta] precipitation within the grain to establish that the T[sub 2]/[alpha]-Al interface is the dominant nucleation site for the noncoherent [delta] phase.

• OSTI ID: 7236606
• Journal Information: Scripta Metallurgica et Materialia; (United States), Journal Name: Scripta Metallurgica et Materialia; (United States) Vol. 30:10; ISSN SCRMEX; ISSN 0956-716X
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
360102* -- Metals & Alloys-- Structure & Phase Studies
ALLOYS
ALUMINIUM ALLOYS
ALUMINIUM BASE ALLOYS
COPPER ALLOYS
DATA
ELECTRON MICROSCOPY
EXPERIMENTAL DATA
INFORMATION
LITHIUM ALLOYS
MAGNESIUM ADDITIONS
MAGNESIUM ALLOYS
MICROSCOPY
MICROSTRUCTURE
NUMERICAL DATA
TRANSMISSION ELECTRON MICROSCOPY
ZIRCONIUM ADDITIONS
ZIRCONIUM ALLOYS