On the mode of decomposition of AlZn alloys

The various phases and the respective ranges of their existence were determined during continuous cooling from temperatures close below the solidus line to R.T. with a rate of 2 K min-l as well as during the subsequent heating in few Al-Zn(40 wt.%)-Mg(X) alloys (X = 0 ; 0.5; 1.0; and 3.0 wt.yo) by means of X-ray phase-analysis, small angle X-ray scattering, differential thermo-analysis, optical microscopy, and X-ray micro-analysis.The most striking features are that even addition of only 0.5 wt.% Mg cause the formation of precursors of the MgZn, equilibrium phase few degrees below the solidus line.Wahrend der kontinuierlichen Abkiihlung von Temperaturen nahe unterhalb der Soliduskurve auf Raumtemperatur und wahreiid der nachfolgenden Aufheizung init 2 K min-l wurden in Al-Zn(40 Gew.yo)-Mg(X)-Legierungen (X = 0 ; 0,5; 1,O; 3,O Gew.yo) mit Hilfe der Rontgen-Phasenanalyse, der Rontgenkleinwinkelstreuung, der Differentialthermoanalyse, lichtmikroskopischer Aufnahmen und der Rontgenmikroanalyse die vcrschiedenen Phasen und deren Existenzbereiche bestimmt.Als iiberraschendes Ergebnis zeigte es sich, da13 schon ein Zusatz von nur 0,5 Gew.% Mg die Bildung von Vorlaufern der MgZn,-Gleichgewichtsphase wenige Grade unter der Soliduskurve bewirkt.

Determination of the phase ranges during cooling and heating of Al‐40wt.%—(0—3) wt.% Mg alloys

Major¹,

Ciach²,

Wendrock³

et al. 1983

Structure of the grain boundary region in an Al–15 at.% Zn and Al–2.0 at.% Zn–1.3 at.% Mg alloy aged at elevated temperatures

Syneček

Simmerska

Bartuška

et al. 1983

Self Cite

The resultsof TEM investigations are presented of the effects of various solution and ageing treatments, cooling and quenching rates as well as of tensile stress a t elevated temperatures on the microstructure of the grain boundary (GB) region of the examined Al-Zn and AlZn-Mg alloys.A pronounced influence was found of partial coherency of GB stable ,8(Zn) precipitates with the a matrix in the Al-Zn alloy on the asymmetry of Zn depleted GB region and on the shape of GB precipitates. The role of GB's as sources and sinks of vacancies and the effect of stress gradients in GB regions were emphasized in the establishment of differences in the nucleation and decomposition characteristics within the GB region as compared to those within the grain interior. The existence of a negative stress gradient towards the GB has been suggested to lead to the observed gradual retardation of transformation kinetics within the GB region in Al-Zn alloys. A rapid quench from annealing to ageing temperature introduced large local stresses close to GB giving rise to a "band of precipitates" on subsequent ageing within the former precipitate free region (PFZ) in Al-Zn-Mg alloy. Similar enhancement of local stresses accompanied by acceleration of decomposition kinetics was also observed in the aged Al-Zn sample subjected to a prior tensile creep exposure within the one-phase region.

Re‐determination of the temperature of the coherent spinodal curve in an‐Al‐15 at.% Zn alloy by transmission electron microscopic and hardness investigations

Kroggel¹

1983

The character of the coarsening of the concentration modulations is studied in an AI-15 at. yo Zn alloy applying TEM investigations (TEM micrographs and diffraction patterns) and hardness measurements in the temperature range from 40 "C to 130 "C. From the TEM investigations the temperature of the coherent spinodal curve is estimated to be (93 f 7)OC. This value agrees fairly well with the result obtained by means of hardness measurements (kink in the TTT-curve occurring at about (84 f 3) "C). The TEM observations of structure revealed in the T,-range below the coherent spinodal a periodic structure relevant to spinodal decomposition. The periodicity of modulations is confirmed by electron diffraction patterns where a clear effect of sidebands near the matrix spots is observed. iiberein, der aus Hllrtemessungen (,,Knick" in der C-Kurve des TTT-Diagramms) erhalten wurde. Die TEM-Untersuchungen zeigen im untersuchten T,-Bereich ebenfalls periodische Strukturen, die auf spinodale Entmischung hinweisen. Die Periodizitiit der modulierten Struktur wird durch Beugungsaufnahmen bestatigt, die deutlich Seitenbander an den Matrixreflexen zeigen. Die Vergroberung der Konzentrationsmodulationen wird in einer AlZn