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

Abstract

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.

The effect of Ti addition on the kinetics and enthalpy of the supersaturated ZnAl alloy phase transformation

“…For the nucleation stage the n values show a greater difference from the theoretical value n = 4. O n the other hand, values of the n coefficient obtained for the growth stage from (15) are in good agreement with those obtained by Pawlowski [8], Pawlowski and Truszkowski [22], and Russew et al [2]. The above-mentioned analysis points out that the value of the start time zo significantly influences the values of the coefficient n in the first stage of phase transformation, while this influence is of smaller importance in the following stages of the examined process.…”

“…6, were obtained. For the growth stage the n values calculated from (15) are very close to the value n = 1 from the Cahn and Turnbull theory. For the nucleation stage the n values show a greater difference from the theoretical value n = 4.…”

“…They observed that impurities of Fe and Si retarded or even stopped the precipitation process. The effect of Mg on the precipitation process of supersaturated AlZn alloys was the subject of investigations carried out by Ciach et al [lo,111,Loeffler et al [12,131,Simerska et al [14], and Major et al [15]. They reported that Mg additions suppress fully or partially the cellular reaction and lead to the retardation of the decomposition of ternary AlZnMg alloys.…”

Phase transformations in Al-Zn alloys solidifying at various rates

“…However, numerous transformations occurring during solidification, heat lreatment or ageing yield in consequence some instability of dimensions or changes of properties thus requiring their further examination [1,2,5].…”