Docsity
Docsity

Prepare for your exams
Prepare for your exams

Study with the several resources on Docsity


Earn points to download
Earn points to download

Earn points by helping other students or get them with a premium plan


Guidelines and tips
Guidelines and tips

Heat treatment of duralumin, Study notes of Thermal Analysis

Conclusions relative to the manufacture and heat treatment of duralumin ... L. M. Cohn, Changes in the physical properties of aliuninimi and its alloys, ...

Typology: Study notes

2021/2022

Uploaded on 09/27/2022

queenmary
queenmary 🇬🇧

4.6

(15)

218 documents

1 / 50

Toggle sidebar

This page cannot be seen from the preview

Don't miss anything!

bg1
HEAT TREATMENT OF DURALUMIN
By P. D. Merica, R. G. Waltenberg, and H. Scott
CONTENTS Page
I. Introduction 271
II. GDmposition and preparation of alloys 273
III. Heat treatment and aging 273
1. Effect of quenching temperature 278
2. Effect of aging temperature 281
3. Effect of temperature of quenching bath 285
4. Effect of prior heating at quenching temperature 293
5. Effect of preheating to 515° Cbefore quenching from lower tem-
peratures 293
IV. Miscellaneous tests 293
1. Density and dilatation 296
2. Electrical resistivity 297
V. Mechanism of hardening during aging after rapid cooling 299
1. Structure of duralumin 306
2. Analogy between the hardening of duralumin and that of steel ... 310
3. Eutectic structure and influence of magnesium 311
VI. Conclusions relative to the manufacture and heat treatment of duralumin
.
314
VII. Summary and conclusions 315
I. INTRODUCTION
The remarkable phenomena exhibited by the aluminum alloy
known as duralumin were discovered during the years 1903-1 911
by A. Wilm^' ^and have been described by him and others. ^' ^' ^' ^
The unusual feature of this alloy is the fact, as was shown by
Wilm, that it can be hardened quite appreciably by quenching
from temperattu-es below its melting point followed by aging at
ordinary temperatures, which consists merely of allowing the
material to stand at these temperatures. The hardness is not
produced by the quenching alone, but increases during the period
*A. Wilm, Physical-Metallurgical investigations of aluminum alloys containing magnesium, Metallurgie
8, p. 225; 1911.
*A. Wilm, The hardening of light alimiinum alloys, Metallurgie, 8, p. 650.
»I,. M. Cohn, Duralumin, Verh. Z. Befordering des Gewerbefleisses, 89, p. 643; 1910.
*L. M. Cohn, Changes in the physical properties of aliuninimi and its alloys, with special reference to
duralumin, Elektrotechnik u. Maschinenbau, 31, p. 430; 1913.
6L. M. Cohn, Duralumin, Elektrotechnik u. Maschinenbau, 30, pp. 809, 829; 1912.
*P. D. Merica, Aluminum and its light alloys. Circular 76 of the Bureau of Standards, 1918, also Chem.
and Met. Eng., 19, pp. 135, 200, 329, 587, 635, 729, 780; 1918.
271
pf3
pf4
pf5
pf8
pf9
pfa
pfd
pfe
pff
pf12
pf13
pf14
pf15
pf16
pf17
pf18
pf19
pf1a
pf1b
pf1c
pf1d
pf1e
pf1f
pf20
pf21
pf22
pf23
pf24
pf25
pf26
pf27
pf28
pf29
pf2a
pf2b
pf2c
pf2d
pf2e
pf2f
pf30
pf31
pf32

Partial preview of the text

Download Heat treatment of duralumin and more Study notes Thermal Analysis in PDF only on Docsity!

HEAT TREATMENT OF DURALUMIN

By P. D. Merica, R. G. Waltenberg, and H. Scott

CONTENTS (^) Page

I. Introduction 271

II. GDmposition and preparation of alloys (^273) III. Heat treatment and aging (^273)

  1. Effect^ of^ quenching^ temperature^278
  2. Effect of aging temperature 281
  3. Effect^ of^ temperature^ of^ quenching^ bath^285
  4. Effect^ of^ prior^ heating^ at^ quenching^ temperature^293
  5. Effect^ of^ preheating^ to^ 515°^ C^ before^ quenching^ from^ lower^ tem-

peratures 293

IV. Miscellaneous^ tests^293

  1. Density^ and^ dilatation^296

2. Electrical resistivity 297

V. Mechanism^ of^ hardening^ during^ aging^ after^ rapid^ cooling^299

  1. Structure of duralumin (^306)
  2. Analogy between the hardening of duralumin and that of steel ... (^310)
  3. Eutectic^ structure^ and^ influence^ of^ magnesium^311 VI. Conclusions relative to the manufacture and heat treatment of duralumin (^3 ) VII. Summary and conclusions (^315)

I. INTRODUCTION

The remarkable phenomena exhibited by the aluminum alloy

known as duralumin were discovered during the years 1 903-1 911

by A. Wilm^' ^^ and have been described by him and others. ^'^ ^'^ ^'^ ^

The unusual feature of this alloy is the fact, as was shown by

Wilm, that it can be hardened quite appreciably by quenching

from temperattu-es below its melting^ point followed by aging at

ordinary temperatures, which consists merely of allowing the

material (^) to stand at these temperatures. The hardness (^) is not produced by the quenching alone, but increases during the (^) period

* A. Wilm, Physical-Metallurgical investigations of aluminum alloys containing magnesium, Metallurgie

8, p. 225; 1911.

* A. Wilm, The hardening of light alimiinum alloys, Metallurgie, 8, p. 650.

» I,. M. Cohn, Duralumin, Verh. Z. Befordering des Gewerbefleisses, 89, p. 643; 1910.

* L. M. Cohn, Changes in the physical properties of aliuninimi and its alloys, with special reference to

duralumin, Elektrotechnik u. Maschinenbau, 31, p. 430; 1913.

6 L. M. Cohn, Duralumin, Elektrotechnik u. Maschinenbau, 30, pp. 809, 829; 1912.

  • (^) P. D. Merica, Aluminum and its light alloys. Circular 76 of the Bureau of Standards, (^) 1918, also Chem.

and Met. Eng., 19, pp. 135, 200, 329, 587, 635, 729, 780; 1918.

272 Scientific Papers^ of the Bureau (^) of Standards [Voi.

of aging, which (^) may be (^) from one to three days. Cohn (see notes

3 and^ 5, p.^ 271) gives^ data^ showing^ the^ increase^ of^ hardness^ of

dm-alumin dm-ing aging, after quenching in water from about

450° C. Upon annealing the alloy so hardened by aging, (^) it is

softened exactly as is hardened steel.

The composition of this alloy usually varies within the following limits:

Per cent

Copper (^) 3-4-

Magnesium o. 4— i. o

Manganese (^) o — o. (^7) Aluminum (^) Balance

Iron (as impurities) o. 4— i

Silicon (as impurities)^ o. 3 — o. 6

Its density is about 2.8. It is used only in the forged or rolled

condition.

This alloy has been produced for some years commercially and

is in demand for the fabrication of parts for which both lightness

and (^) strength are required, such as for aircraft. (^) Its tensile strength

will average 50 000 to 60 000 pounds per square inch after appro-

priate heat treatment, such as that described by Wilm.

With the pmpose of ascertaining whether the heat treatment

described by him actually developed the best mechanical proper-

ties possible for dm-alumin, the authors undertook a study of the

effect of variation in heat-treatment conditions, that is, quenching

temperatin-e, aging^ temperatiu-e,^ etc.,^ upon^ these^ properties^ and,

in connection with another investigation,^ a study of the effect of

chemical composition upon them.

E. Blough^ had^ already^ called^ the^ attention^ of^ one^ of^ the^ authors

to the fact that the amount of hardening produced by heat treat-

ment was influenced quite markedly by the temperature from

which the material was quenched, a most interesting fact which

was not brought out by Wilm's published investigations, which

mentioned merely the effect of aging after quenching from one

temperature, in the neighborhood of 450° C.

An explanation was sought also for the mechanism of hardening

during aging of this alloy, and additional data were obtained

bearing upon this phase of the matter.

The experiments^ here^ described^ were^ carried^ out^ partly^ in^ the

laboratories of^ the^ Bureau^ of^ Standards^ and^ partly^ in^ cooperation

7 p. D. Merica, R. G. Waltenberg, and A. N. Finn, The tensile properties and resistance to corrosion of

rolled light alloys of aluminum and magnesitim with copper, with nickel, and with^ manganese,^ Techno-

logic Paper No. 132 of the Bureau of Standards, 1919.

274 Scientific^ Papers^ of the^ Bureau^ of Standards^ [Vol.^ IS

electric furnace,^ quenching^ in^ water,^ and^ aging^ at room or other

temperatures for^ different^ periods.^ The^ results of these tests are

given in Table 2.

TABLE 2,—^The Tensile Properties and Scleroscope Hardness of Rolled, of Annealed,

and of Heat-treated Aluminum-Copper-Magnesium Alloys

Number

As rolled

Sclero-

hardness

magni-

fying er

Tensile strength

Elonga-

tion in 2 inches

After annealing at 422" C

Sclero- scope

hardness

magni-

fying hammer

Tensile strength

Elonga-

tion in 2 inches

CI

C2.

C3.

C

CS.

C6.

C

C8,

C

CIO.

Cll.

C12.

Lbs./in. 49 000 48 400 48 600 49 600 25 800 23 600 23 600 34 900 35 700 34 000 38 400 38 600 (^37 ) 35 900 37 500 37 700 35 300 38 500 38 100 44 200 45 500 45 300 38 100 38 100 41 200 43 200 41 200 44 800 44 600 47 500 56 700 52 900 58 400 38 900 38 600

Per cent

Lbs./in. 33 000 33 100 32 700

Per cent

Merica, WcdtenbergA (^) Heat Treatment (^) of Duralumin (^275)

TABLE 2.—The Tensile^ Properties^ and^ Scleroscope^ Hardness^ of^ Rolled,^ of^ Annealed,

and of Heat-treated^ Aluminum-^ Copper-Magnesium^ Alloys—Continued

Hmnber

CI

01

cs

C

C

C

C

CIO

cu

C

After heat treatment consisting of quenching in water and aging

Quenched from 478° C

Aging

Aged

at 110°

Days

Aged

at 20°

Days

11 11 11

Scleroscope

hardness

magnifying hammer

Tensile strength

Lbs./in.a 36 870 37 080 36 260

16 830 16 510 16 510

28 020 25 810 25 440

29 300 28 910 30 280

33 220 32 580 31 930

31 050 33 790 31 640

42 350 42 530 42 350

46 400 47 030 48 900 47 650 31 790 30 450 30 070

38 030 37 630 38 430

50 450 48 950 51 740 50 880 38 330 38 730 35 910

Elonga- tion in 2 inches

P.ct.

Quenched from 510° C

Aging

Aged

at 110°

Days

Aged

at 20°

Days

1

Scleroscope

hardness Tensile

magnifying

hammer

strength

Lbs./in. 17 38 030 37 220 27 48 120 47 210 16 670

8

Elonga- tion in 2 inches

P.ct.

T5.

Merica, Wallenberg,! Scott (^) J Heat^ Treatment^ of^ Duralumin^277

All of the^ alloys^ except^ those^ containing^ no^ copper (Nos. C

C4, and^ C9)^ show^ an^ increase^ of^ hardness^ of^ the^ hest-treated^ speci-

mens over that of the annealed samples. The increase of hardness

in those alloys containing copper, but no magnesitmi, is smaller

than that in those containing both, but is quite definite. This is

shown in the following table

Number of alloy

Increase of ten- sile strength of heat-treated

alloy (510° C)

ovei annealed

alloy

Alloys containing no copper:

C ...

Per cent

  • 2

C4 -f 3

C9 —^4

Alloys containing copper but no magnesium:

C3 +

C5.- +

Alloya containing both copper and magnesium:

CI 45

Cll 56

C12. 110

It is noticed that the best mechanical^ properties are produced

by quenching from the higher^ temperatures^ (500 to 525° C). This is shown in^ Table^ 3, giving^ further^ data^ on^ two^ alloys,^ C8 and Cii, and^ will^ be shown^ more^ clearly^ below. 121040°— 19 2

278 Scientific^ Papers^ of the^ Bureau^ of Standards^ [Voi. 15

TABLE 3.—Effect of Quenching Temperature on Tensile Properties

Alloy C8 Alloy Cll

Quenching

Aging Mechanical properties Aging Mechanical properties

temperature

20° C 110° C

Sclero- scope

hard-

ness

Ultimate tensile strength

Elonga-

tion in 2 inches

20° (^) C 110° (^) C

Sclero- scope

hard-

ness

Ultimate tensile strength

Elonga-

tion in 2 inches

37r (^) C...

Days

7 7 13 13 7 7 13 13 7 7 11 11 [ ^^ 11 8 [ 8 [ 11 11 { 11 I 11

( 1 '' 11 8 [ 8

I ^^ 1 13

Days

11

12

}"

22

....

Lbs./in. 27 260 1 26 220 J^29 1 29 130 J^39 1 40 160 J

J^46
J^48
J 47 230

f 44 130 1 44 910

J

I 44
J^46
J^53
I 53 000
J^34

Per ct.

Days

7 7 13 13 7 7 13 13 7 7 11 11 11 11 8 8

Days

I 25
1 ^^
\ 28
1 ^^

Lbs./in. { 35 900 I 36 550 J^35 1 35 020 J

J

j 50 450 1 48 950 J^51 1 50 880 J^52 1 52 590 J^51 1 50 870 J

Per ct.

422° C...

478° C

500° (^) C

510° C...

1 520° C .

525° (^) C

533«»C

r 48 370 t 47 060

Not only does the hardness increase after heat treatment, but so also does the ductility, as evidenced by the elongation in the tensile test. This is shown in Tables 2 and (^) 3.

  1. EFFECT OF QUENCHING TEMPERATURE

In Fig. I are shown the scleroscope hardness values of Cii quenched in water (20° C) from different temperatures and aged

at room^ temperature^ for^ periods^ of^ time^ from a^ few^ hours^ to^30 days. The form of these aging curves is similar to that shown by Cohn (see notes 3 and 5 on (^) p. 271) ; that is, the hardness increases

after quenching,^ at^ first^ rapidly^ and^ then^ more^ slowly.^ It^ is^ fur-

28o Scientific Papers (^) of the Bureau (^) of Standards' [Vol. IS

ther evident that the maximum hardness attained increases with

the temperatm*e up to approximately 520° C.

The effect of quenching temperature is also shown very nicely

in an experiment of which the results are shown in Fig. 2. Two

strips of 0.087-inch sheet of alloy N34 were used. The strip (^) was

placed in the furnace for heating in such a manner that a nearly

linear temperature gradient^ existed^ between^ the^ two ends,^ as

Ift ^ "O ^ Ifj "^ (^) ^

shown by thermocouples placed along the strip. Upon attaining

the desired range of temperattires, the strip was quenched in boiling water and aged 20 hours at 110°^ C. The scleroscope hardness was then determined along the axis of the strip, and is shown in Fig. 2 as a function of the distance from one end of the sample. The distance may be regarded as a rough temperature

M^ka.waitenberg.-j //^^^ Treatment

of Duralumin^281

scale, the outside temperature^ limits^ having^ been^ determined^ and

marked on^ the^ curve.^ One^ strip^ was^ quenched^ when^ the^ two

ends were^ at 520 and^ 280°^ C,^ respectively;^ the^ other,^ when^ the

ends were at 490 and 210°^ C, respectively. Beginning at about

300° C, the effect of increased quenching temperature, other fac-

tors remaining alike, is to increase the hardness after aging until

a temperatiu'e of about 520° C is reached. Beyond that temper-

ature the hardness again decreases; the material becomes covered

with a dark gray oxide coating and generally also with blisters,

marking the temperature of eutectic melting. The effect of heat-

ing to temperatures around 300°^ C is chiefly to anneal the specimen

and to give lower values of the hardness (minimum^ on the curve)

than is given by heating^ at lower^ temperatures.

  1. EFFECT OF AGING TEMPERATURE

In Table 4 are given^ results of tests showing the effect of tem-

perature of quenching^ bath and^ of aging^ carried out in the bath.

The samples used were strips of (^) A1-12 quenched from 520° (^) C.

The increase of strength witli time of aging (^) is evident.

Merica, Waltenberg,! ScoU J Heat^ Treatment^ of^ Duralumin^283

A more complete^ picture^ of^ the^ phenomenon^ of^ hardening^ by

aging at different^ temperatures^ is^ obtained^ from^ Figs.^ 3, 4, and^ 5,

based upon^ data^ obtained^ on^ specimens^ of^ N34.^ The^ sclerocsope

values of^ Fig.^3 were^ obtained^ upon^ samples^ quenched^ in^ boiling

water from^ two^ temperatures,^515 and^ 525°^ C,^ and^ aged^ at^ differ-

ent temperatiu-es.^ The^ same^ figures^ are^ replotted^ in^ Fig.^4 in

different form.

T/fr>f af /Jyin^ //> JJayj.

Fig. 3. Effect of aging at different temperatures on the^ scleroscope^ hardness^ of samples

quenched from 51 5°^ C and 52 5° C. {Alloy N-34)

It is noted (i) that the rate of hardening increases as the tem-

perature of aging (^) increases, (2) that the maximum hardness (^) is obtained by aging at temperattu-es above 100° (^) C, and (^) (3) that at aging temperatures above 140° C the hardness eventually drops after reaching its maximum.

284 Scientific Papers (^) of the Bureau (^) of Standards [Vol. (^) IS

'^ifcuudc?^ Bu/Aj/u^£:?/^ -^ S'^^c/^^i:^//^ »^<?:?s^o^^/:?^

286 Scientific Papers (^) of the Bureau (^) of Standards [Voi.is

effect of the temperature of the quenching bath indicated in these

results. Those samples quenched to 150° C gave practically the

same results as those quenched to 230° C, although there is a

slight improvement in the tensile properties of those quenched to

150° (^) C over those quenched to 100°^ C.

In Table^6 are shown results^ of^ tests^ to^ determine^ the^ effect^ of

aging at room temperature after aging^ at the temperature of the

quenching bath. It will be noted^ that^ there^ is^ only^ a slight

increase in the strength of the alloy produced by aging at 20°^ C

after aging at the temperature of the quenching bath.

Merica, Waltenberg, Scott (^) ] Heat^ Treatment^ of^ Duralumin^287

g Q Pi , « , «iO ^g >ao U <J »o .0^ t>k^ m

1 1 Jr. tS| a

•« a

n .S

. o

i

)

1

^ ^ KJ {Q 1 S (^) eg : ^ ^

II

Per

cent 23.5 26.0 21.5 26.0 22.5 (^) 22. 53 • 53 S

•St

il 52 rt^ CM^ to^ TJ-^ Tf^ to

3 ^^ ^^ ^^ *^ *^ *

^CO st^ •<1- CO

il

2

I

Is

II

C3\ t«. CO CO CO (^) t^ CO CO CO

II

S

§ « to^10 to

CS? to ^ .0 to

OtotOOOiOOO ;o;HvgvgvocMvo^

Ig

Si

42

950 43

600 49

300 50

450 49

750 48

(^550) §1111 |S|

(^1) 6"

g

Ij

J3 53 2 JQ

o J5 (^53) CO CO

«

II

4§§ ^55?^ i^ 1 Z^ s?^ S

.a

1

Is il g^ S^ {Q^ S ^^ S^ S^ s^ ?5^ s^ J?^ ^^ s

II (^) goo to cd 5^ 2 53 53

to to 10 ;5 S 53 5^ 53 5^

1 —^

45

750 45

025 44

900 44

450 44

550 44

700 47

100 45

950 47

000 47

000 48

250

i3«

::i^ 2 ^ ^ ^ CO CO 0^ CJ^ ? 00 s s

Merda, Waltenberg,

Stott ]^ Heat^ Treatment^ of^ Duralumin^289

  • g

5S 55 S ^

irt a> o^ 06

47

600

b

47

100 50

400 50

750

:? ^

CO CO CO CO a a

n 10 Tl^ CM COCM (^) CM-^ CMCM a

51

450 48

500

a

54

600

a

53

850

S ^

^ (^) :

00 c^

CM CM (^) S s

: 5?

^ ^ « a

«MCM COcq

10

a

CM a

CM CM (^) s s

290 Scientific Papers (^) of the^ Bureau^ of Standards^ \V0L

Ir, JS !^ S> iTi Q"