










































Study with the several resources on Docsity
Earn points by helping other students or get them with a premium plan
Prepare for your exams
Study with the several resources on Docsity
Earn points to download
Earn points by helping other students or get them with a premium plan
Community
Ask the community for help and clear up your study doubts
Discover the best universities in your country according to Docsity users
Free resources
Download our free guides on studying techniques, anxiety management strategies, and thesis advice from Docsity tutors
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
1 / 50
This page cannot be seen from the preview
Don't miss anything!
CONTENTS (^) Page
II. GDmposition and preparation of alloys (^273) III. Heat treatment and aging (^273)
IV. Miscellaneous^ tests^293
V. Mechanism^ of^ hardening^ during^ aging^ after^ rapid^ cooling^299
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
material (^) to stand at these temperatures. The hardness (^) is not produced by the quenching alone, but increases during the (^) period
8, p. 225; 1911.
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
450° C. Upon annealing the alloy so hardened by aging, (^) it is
The composition of this alloy usually varies within the following limits:
Copper (^) 3-4-
Manganese (^) o — o. (^7) Aluminum (^) Balance
Silicon (as impurities)^ o. 3 — o. 6
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-
temperatin-e, aging^ temperatiu-e,^ etc.,^ upon^ these^ properties^ and,
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
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
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
and of Heat-treated Aluminum-Copper-Magnesium Alloys
Number
As rolled
Sclero-
fying er
Tensile strength
tion in 2 inches
After annealing at 422" C
Sclero- scope
fying hammer
Tensile strength
tion in 2 inches
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
Lbs./in. 33 000 33 100 32 700
Merica, WcdtenbergA (^) Heat Treatment (^) of Duralumin (^275)
and of Heat-treated^ Aluminum-^ Copper-Magnesium^ Alloys—Continued
Hmnber
CI
01
cs
C
C
C
C
Quenched from 478° C
at 110°
at 20°
11 11 11
Scleroscope
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
at 110°
at 20°
1
Scleroscope
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
C4, and^ C9)^ show^ an^ increase^ of^ hardness^ of^ the^ hest-treated^ speci-
mens over that of the annealed samples. The increase of hardness
shown in the following table
Number of alloy
Increase of ten- sile strength of heat-treated
alloy
C9 —^4
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
20° C 110° C
Sclero- scope
Ultimate tensile strength
tion in 2 inches
20° (^) C 110° (^) C
Sclero- scope
Ultimate tensile strength
tion in 2 inches
37r (^) C...
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
11
12
}"
22
....
Lbs./in. 27 260 1 26 220 J^29 1 29 130 J^39 1 40 160 J
f 44 130 1 44 910
J
7 7 13 13 7 7 13 13 7 7 11 11 11 11 8 8
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
478° C
500° (^) C
1 520° C .
525° (^) 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.
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
of Duralumin^281
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
a temperatiu'e of about 520° C is reached. Beyond that temper-
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.
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.
Fig. 3. Effect of aging at different temperatures on the^ scleroscope^ hardness^ of samples
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
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
increase in the strength of the alloy produced by aging at 20°^ C
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
n .S
. o
i
)
1
^ ^ KJ {Q 1 S (^) eg : ^ ^
Per
cent 23.5 26.0 21.5 26.0 22.5 (^) 22. 53 • 53 S
•St
3 ^^ ^^ ^^ *^ *^ *
^CO st^ •<1- CO
il
2
I
Is
II
C3\ t«. CO CO CO (^) t^ CO CO CO
CS? to ^ .0 to
OtotOOOiOOO ;o;HvgvgvocMvo^
42
950 43
600 49
300 50
450 49
750 48
(^550) §1111 |S|
(^1) 6"
g
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
Stott ]^ Heat^ Treatment^ of^ Duralumin^289
5S 55 S ^
irt a> o^ 06
47
600
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