Effect of cold compression on precipitation and conductivityof an Al–Li–Cu alloy

Abstract

SummaryTransmission electron microscopy has been used to investigate the effect of increasing the degree of deformation applied by cold compression on the ageing kinetics and electrical conductivity response of an Al-Li-Cu alloy containing Mg and Ag. When cold compressed greater than 3%, the increased dislocation density accelerates the widespread precipitation of the T 1 phase resulting in an enhanced age hardening response. The lengthening rate of T 1 precipitates is also reduced in this cold compressed condition owing to the reduced local solute supersaturation, a result of the widespread precipitation of T 1 plates. Cold compression by less than 3% does not increase the age hardening response, and the precipitation of GP zones/θ appears to be suppressed. Precipitation of the T 1 phase is also not significantly enhanced compared with that of the more than 3% cold compressed conditions. The anomalous decrease in electrical conductivity is associated with the nucleation and growth of the T 1 phase. Strain fields around T 1 precipitates combined with the increased volume fraction of T 1 are thought to be the cause of the anomalous conductivity behaviour.

Influence of Industrial Heat Treatments on the Precipitation Kinetics of an Al-Cu-Mg-Ag-Zr Alloy

“…The observed microstructure and good mechanical properties at this temper confirm that applying plastic deformation accelerates the precipitation kinetics by approximately one order of magnitude [33]. Quantitative evaluations of the T 1 platelets precipitates presentedin Figure 7b show that the average chemical composition, as estimated from the concentration composition profile based on the isoconcentration surface that contains more than 6 at.% Li (calculated over 20 precipitates containing in different reconstructed volumes), is (13±1) at.% Li, (11±1) at.% Cu, (3±1) at.% Mg and (1.5±0.4) at.% Ag.…”

Influence of Natural Ageing and Deformation on Precipitation in an Al–Cu–Li Alloy

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Precipitation hardening alloys based on the Al-Cu-Li system are experiencing currently a strong research effort in the framework of the development of new alloys, [1,2] particularly for aerospace components. [3][4][5][6][7] The main strengthening precipitate in this system is the T 1 phase of nominal composition Al 2 CuLi that forms very thin platelets of high aspect ratio on the {111} planes of the Al matrix. [3][4][5][6][7] The main strengthening precipitate in this system is the T 1 phase of nominal composition Al 2 CuLi that forms very thin platelets of high aspect ratio on the {111} planes of the Al matrix.

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“…[3,8,9] Decreus et al [10] have studied in detail the influence of alloy chemistry on the precipitation sequence of two recently developed alloys. [3,6,7,14,15] Seemingly it was shown to be relatively independent on natural ageing [7] contrarily to most other precipitates in Al alloys (such as in 6000 or 7000 series), however the data concerning this point is scarce. Numerous studies on earlier generations of alloys have shown that nucleation of the T 1 phase depends strongly on the presence of minor solute species [7,[11][12][13] and on the presence of dislocations.…”

“…These alloys, where the main solute elements Cu and Li are often supplemented with additions of Mg and Ag, show a complex precipitation sequence. [3][4][5][6][7] The main strengthening precipitate in this system is the T 1 phase of nominal composition Al 2 CuLi that forms very thin platelets of high aspect ratio on the {111} planes of the Al matrix. [3,8,9] Decreus et al [10] have studied in detail the influence of alloy chemistry on the precipitation sequence of two recently developed alloys.…”

“…Numerous studies on earlier generations of alloys have shown that nucleation of the T 1 phase depends strongly on the presence of minor solute species [7,[11][12][13] and on the presence of dislocations. [3,6,7,14,15] Seemingly it was shown to be relatively independent on natural ageing [7] contrarily to most other precipitates in Al alloys (such as in 6000 or 7000 series), however the data concerning this point is scarce. The aim of the present paper is to clarify, on the AA2198 alloy, the effect of the processing conditions preceding artificial ageing at 155°C on the precipitation processes and related strengthening.…”