ANOMALOUSLY AMPLITUDE-DEPENDENT INTERNAL-FRICTION PEAKS IN ALUMINIUM CONTAINING 0.12 wt % OF MAGNESIUM

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ANOMALOUSLY AMPLITUDE-DEPENDENT INTERNAL-FRICTION PEAKS IN ALUMINIUM

CONTAINING 0.12 wt % OF MAGNESIUM

Q. Fang, T. Kê

To cite this version:

Q. Fang, T. Kê. ANOMALOUSLY AMPLITUDE-DEPENDENT INTERNAL-FRICTION PEAKS IN ALUMINIUM CONTAINING 0.12 wt % OF MAGNESIUM. Journal de Physique Colloques, 1985, 46 (C10), pp.C10-227-C10-230. �10.1051/jphyscol:19851051�. �jpa-00225435�

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JOURNAL DE PHYSIQUE

Colloque C10, suppl6ment au 11'12, Tome 46, dbcembre 1985 page C10-227

ANOMALOUSLY AMPLITUDE-DEPENDENT INTERNAL-FRICTION PEAKS IN ALUMINIUM CONTAINING 0.12 wt I OF MAGNESIUM

Q.F. FANG AND T.S. KI?

Institute of Solid State Physics,Acadernia Sinica, Hefei, China

Abstract

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Anomalously amplitude-dependent internal-friction.

peaks were observed[ in Al-0.12'wt % Kg after the specimen was subjected to an ingenious procedure of mechanical and thermal treatment. The height of the peak can reach 0.1 which is one order of magnitude higher than those observed previously. !ho types of amplitude-dependent internal-friction peaks were observed. Salient features of the co-existing strain-aging internal friction peak, the temperature internal-friction peak, and the amplitude internal-friction peak were systematically studied.

I. Introduction

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Since the anomalously amplitude-dependent internal- friction peaks (i.e. the internal friction decreases with an increase of strain amplitude) were observed in cold-worked aluminium containing 0.5 wt % of copper /I/, or 0.03, 0.1 , ^0.4^wt% of magnesium /2, 3/, the reproducibility of the experimental results was not yet very sa- tisfactory. The previous deformation and annealing treatments upon the specimen adopted so far can be classified into two main categories:

( 1 ) to anneal a heavily cold-worked specimen so that it is only par- tially recrystallized. (2) To anneal a cold-worked specimen to comple- te recrystallization and then deform it (stretch or twist) slightly

just beyond the yield pint. In this report, these two types of treatments were combined, i. e. to anneal the cold-worked specimen to par- tial recrystallization, deform it slightly and then anneal it at a proper intermediate temperature. Ttro ty es of amplitude-dependent internal-friction peaks were observed: (a7 The high-amplitude side of the peak decreases slowly and stays at an almost constant high value.

(b) The high-amplitude side of the peak decreases rapidly and contf- nuously to reach a very small value. The second type of peak is what we called anomalously amplitude-dependent internal-friction peak.

II. Amplitude-dependent Internal-friction Peaks during Strain Aging:

at Room Tbm~erature

An A1-0.12 $ Mg specimen (cold worked to 84 % RA) was annealed succes- sively at 250, 275, 300, 325 and 350% for 1 h and was then twisted in-situ of an inverted torsion pendulum apparatus to r0.3 % ^X 2 (i. e.

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19851051

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C10-228 JOURNAL DE PHYSIQUE

twist the wire in one sense of rotation to 0.3 % and then twist it back to the original position) at 21°C. Internal friction measurements

(f = 2.3 HZ) were taken at 2IeC immediately after the twisting treatment. The variation of internal friction as a function of aging time is shown by Fig. la. The strain amplitude corresponding to the internal-friction value shown by the curve is 1.8 X 10'~. An aging internal- friction peak appeared around 102 min. The variation of internal friction as a function of strain amplitude at the aging time marked by A, B and C on the curve in Fig. la is shown in Fig. Ib. It is seen that the internal friction increases monotonical with incr&sfirg strain

amplitude (normal amplitude-dependence) along curves C and B and a peak appeared on curve A. This peak belongsto the first type of amplitude peak as classified in I.

Fig. la. Variation of internal friction Fig. Ib. Variation of in- as a function of aging time at 2I0C. ternal friction as function Specimen annealed at 250 to 350°C and of strain amplitude: Curves twisted to *0.3$~2 at 2I0C. A , B, C: at aging times of

91, 100 and 106 min.

Another 81-0.12 % Mg specimen (cold-worked to 91 % RA and left at room temperature for 2 months) was annealed at 350°C for 1 h and then twis-ted at 10aC to rt0.25 5 X 2. Internal friction measurements were taken at 10°C with f = 1.4 Hz. The aging internal-friction curve shown in Fig. 2a corresponds to a strain amplitude of 0.84 X PO-^

.

^{The va-}

riation of internal friction as a function of strain amplitude at the aging time marked by 1 , 2, 3, 4, 5 on the curve in Fig. 2a is shown in Fig. 2b. It is seen that the internal friction reaches a high value of 0.08. The amplitude internal friction curves shown in Fig. 2b are of the first type.

Fig. 2a. Variation of internal Pig. 2b. Tariation of internal frlction as a function of aging friction as a function of strain time at 10%. Specimen annealed amplitude: Curves 1 , ^{2, 3, 4,}⁵^:

at 350°C and twisted toY0.25 % at aging times of 23, 43, 59, 94

X 2 at 10°C. and 221 min.

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The specimen aged at 1 8 O C (Fig. 3 9 ) was annealed at 27!jaC for 1 h, twisted at 18°C to *O.3 $ x 2 , annealed again at 2 5 0 ~ ~ for 1 h (annealed twice), and internal friction measurements (f = 1 . 8 Hz) were taken during the aging at 1 8 O C . The internal-friction curve shown by Fig. 3a corresponds to a strain amplitude of 1 X lom5. The amplitude curves corresponding to the aging times marked by A, B, C , D , E on the curve of Fig. 3a are shown in Fig. 3b. It is seen that the internal friction is extremely high and the amplitude peaks belong to the second type.

Fig. 3a. Variation of internal Fig. 3b. Variation of internal friction as a function of aging friction as a function of time at 18OC. Specimen annealed strain amplitude: Curves A, B, at 275'C, twisted to 2 0 . 3 $ x 2 C , D , E: at aging times of 1 8 ,

at 7 8 O C , and annealed again at 80, 1 0 0 , 142, 166 min.

2'50 OC

.

111. Amplitude-dependent Internal-friction Peaks Appeared Around the Tem~erature Region of the Temperature Internal-friction Peak The specimen aged at 2I0C (Fig. l a ) was annealed at 350°C for 1 h and internal friction measurements (f = 2.2 HZ) taken with descending temperatures with a strain amplitude of 2' x l o 5 . A broad temperature- internal-friction peak appeared around the temperature region of 50 to tOO°C as shown by Fig. 4a. m e amplitude cumes corresponding to the temperatures A , B, C , D , E , F marked on the curve of Fig. 4a are shown in Fig. 4b. The internal friction is extremely high and the amplitude peaks belong to the second type. Lt is to be noticed that the peak of the amplitude curve shifts considerably toward lower amplitudes with

Fig. 4a. Variatian of internal fric- tio,n as a function of temperature of measurement. Specimen aged at 21 O C

(Fig. la), and then at 750°C.

Fig. 4b. Variation of internal friction as a function of strain amplitude. Curves A, B, C , D , E , F: at 7 4 , 6 0 , 51, 41 , ^{29, 20°C.}

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C10-230 JOURNAL DE PHYSIQUE

an increase of the temperature of measurement.

An 81-0.12 % Mg specimen (cold-worked to 84 '$ RA and left at room temparature for 6 months) was annealed at 275°C for 1 h and twisted at 1 8 @ ~ to 4 0.3 % x 2. It was then annealed at 250°C for d h after an aging at 18"C. Internal friction measurements (f = 1.2 Hz) were taken with ascending temperatures up to 240'C and then with descending temperatures. Internal friction curves corresponding to a strain amplitude of 1 x 10-5 are shown in Fig. 5a. It is seen that the internal friction increases rapidly after the temperature was lowered to about 100.C and a peak appeared at about 608C. The amplitude curves corresponding to the temperatures range from 94 to 32*C shown in Fig. 5b belong to the second type of amplitude peak. However, the peak shifts toward higher amplitudes with an increase of the temperature of measurement, which is quite different from that shown in Fig. 4b. In this temperature range, the modulus curve (fe vs temperature) also behaves t?tbnormally fn. tha% it decreases with a decrease of temperature.

Fig. 5a. Tariation of internal fric- Fig. 5b. Variation of internal tion and elastic modulus as a func- friction as a function of tion of temperature of measurements. strain amplitude. Curves A, B, Specimen annealed at 275"C, twisted C, D, E, F: at 32, 52, 56, 72, at 118C to 20.3 % x 2, and annealed 81, 94OC.

again at 250eC.

IV. Discussions

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Ekperimental results shown above indicate that the position and height of the aging p~esk, amplitude peak, and temperature peak are very sensitive to the previous treatments subjected to the specimen before the measurements. It is considered that: ( 1 ) The amplitude dependent internal-friction peaks during the aging at room temperature peaks of the 1st type are originated from the thermally assisted unpinning of dislocatio,ns, as formulated by Blair, Hutchison and Rogers based an the model of Teutonico, Granato and ~ucke./4/ (2) The anomalously amplitude-dependent internal-friction peaks (peaks of 2hd type) appeared around the region of the temperature internal-friction peak are originated from the movement of the solute atoms ( ~ g )

within the dislocation core resulted from the "dragging" exerted by the inhomogenous stress field of the moving kinks on the dislocations.

/1/ This movement can be resolved into a longitudinal and a transverse component. Each component will give rise to an anomalously amplitude- dependent internal-friction peak of different characteristics.

~ e f erence

1 T. S. KG, Phys. Rev. 78, 420 (1950).

2 T. 5 . KG, C. 9. Changyand Z. S. Chang, Acta Physica Sinica 2,

270 (1966).

/3/ Z. S. Pan, 2 . G. Wang, Q. H. Kong, and T. S. KG, Acta Physica Sini-

a,

¹¹⁸⁰⁽1980) ; Materials Science and Engineering f 01( 1981 )

.

/ 4 / D. G. Blair, T. S. Hutchison, and D. H. Rogers, Can. J. Phys. 49,

633 (1971); L. J. Teutonico, A. V. Granato, and K. Lucke, J.app1.

Phya. 2, 220 (1964).