On the decomposition behaviour of supersaturated Al‐Zn‐Mg alloys in dependence on heat treatment

Self Cite

The structure of an A1-1.9 at.% Zn-1.3-at.yo Mg mother alloy with additions of Mn and Fe, respectively, were investigated by TEM and microprobe analysis for t w o different heat treatments, namely direct quench from 490 "C t o 160 "C and a two-step ageing treatment (preageing at RT for 7d before storing at 160 "C), to explain the differences in the course of the hardness obtained during the ageing at 160 "C. The differences of the structure observed are explained in terms of the tendency of the additives to form intermetallic phases, particularly in the grain boundaries.Die Struktur einer AlZn (1.9 At.-%) Mg(1.3 At.-%)-Basislegierung niit Beigaben voii Mn bzw. F e wurde mittels TEM und Mikroanalysator fur zwei verschiedene Wiirniebehandlungen, niimlich direktes Abschrecken von 490 "C auf 160 "C und eine Zweistufenalterung (7d Vorlegerung bei RT vor dem Altern bei 160 "C), untersucht, um die Differen-Zen in den geniessenen Verliiufen der Hiirtekurven bei 160 "C zu erkliiren. Die beobachteten Unterschiede in den Strukturen werden auf die Tendenz der Beigaben, intermetallische Verbindungen vor allein in den Korngrenzen zu bilden, zuriickgefuhrt.

Section: Precipitates In the Grain Boundariesmentioning

confidence: 53%

The Effect of Additions of Mn and Fe on the Structure of an Al‐2 at.% Zn‐1 at.% Mg Alloy

Löffler

Korngiebel

Salawa

1986

Self Cite

On the influence of impurity additions and quenching temperature on the course of the microhardness (HV) during a two‐step ageing treatment of an Al‐2.0 at.%Zn‐1.3 at.%Mg Alloy

Gerlach

Löffler

1983

A pure as well as the analogous technical alloy were directly quenched from T , = 400 "C or 490 "C to T,, preaged at T , (ranging between 50 "C and 160 "C) various times (t,), and subsequently postaged a t R.T. up to tpost = 42 d.-Ageing the samples below the upper limit temperature of the homogeneous formation of G.P. zones (Thn) no essential difference in the course of the HV-number attained after ono-as well as two-step ageing in dependence on the addition of impurity atoms and T , could be found.-Contrary to this behaviour after pre-ageing a t T , > Tiln and postageing a t R.T. a variation of both T, and the content of impurity atoms shows a considerable effect. The reason is the difference in the density of nucleation sites for heterogeneous formation of precipitates of the 7'-and/or 7-phase in depcndence of T q and impurity content.Eine reine und die analoge technische Lcgierung wnrden direkt von T, = 400 "C bzw.490 "C auf T , zwischen 50 "C und 160 "C abgeschreckt und bei diesen Temperaturen verschiedene Zeiten (t,) vorgelagert und nachfolgend bis zu tpo8t = 42 d bei RT nachgealtert.-Altert man die Proben bei T, < T h n (obere Grenzo der GP-Zonen-Bildung), so werden sowohl nach Ein-als auch nach Zweistufenalternng keine wesontlichen Unterschiede im Gang der Mikroharte (HV) in Abhiingigkeit von T , und dem Gehalt an Verunreinigungselement en gefunden.-Im Gegensatz dazu ergeben sich nach Voralterung bei T, > T h n und RT-Nachlagerung starke Differenzen zwischen beiden T, und Legierungen. Der Grund sind die Unterschiede in den Dichten der Keimlagen fur die heterogene Bildung von Ausscheidungen der q'-und/oder 7-Phase in Abhangigkeit von T, und dem Gehalt an Verunreinigungen.

The effect of vacancy‐rich clusters on the decomposition processes in Al‐Zn‐Mg alloys

Lendvai

1984

1ntroduct)ionSince the early works of HARDY and POLMEAR the existence of vacancy-solute atom clusters (VRC) often turned up in the literature, in inost cases to explain the differences of the precipitate structures after different quenching treatments. The aim of this paper is to review the results concernirtg the forrnation of the VHC and their effect on the decortipsition processes. VRC as nucleation sites for metastable and stable precipitatesThe existence of VRC has been assumed to explain the differences in the precipitate structure of Al-Zn-Mg alloys after direct quench, UQ, and indirect quench, 1&, to the ageing temperature, T,. I n case of 1Q the alloy is generally water quenched to 0 or 20 "C, kept at this temperature for a short time (order of one minute) and thereafter aged at T,. 1982) we can conclude that VRC play an important role in the precipitation of the metastable (7') and even of the stable ( q ) phase when G P zones are not formed prior to or a t the beginning of the ageing at T,. I A o~~~,~;~ 1982.) investigations. The observations were interpreted in most cases by the formation of V l t C during the quench and/or during short ageing times (order of 10 sec) a t room temperature. The VltC then act as nucleation sites for the precipitation of the metastable or stable precipitates when the alloy is up-quenched to T, > TI,. I t is generally agreed (L~FELER et al. 1983) that the number of VRC depends sensitively on the quench procedure, i.e. on the temperature of solution treatment and of the quenching bath, on the quenching rate (e.g. air cooling, oil quench, water quench etc.) or on conditions of step quenching. Above a certain critical temperature, which depends on the alloy composition and on the quenching procedure, VRC are not formed and consequently the precipitation of the metastable or stable precipitates l)