Effects of heat treatment on the mechanical properties of 6201 aluminum alloy wire

Vietnam Journal of Science and Technology 57 (3A) (2019) 11-20
doi:10.15625/2525-2518/57/3A/13936

EFFECTS OF HEAT TREATMENT ON THE MECHANICAL
PROPERTIES OF 6201 ALUMINUM ALLOY WIRE
Huynh Cong Khanh
Faculty of Materials Technology, Ho Chi Minh City University of Technology, VNUHCM
268 Ly Thuong Kiet Street, Ward 14, Dist. 10, Ho Chi Minh City
*

Email:

Received: 13 July 2019, Accepted for publication: 18 September 2019
Abstract. Type 6201 aluminum alloy wires are produced by drawing 4.7 mm diameter billet-onbillet extruded redraw rod down to 2.7 mm diameter wires. Before drawing, the first group of
redraw rod coils was annealed at 480 oC for 4 hours to reduce the hardness of the redraw rod.
The second group of redraw rod coils was drawn without annealing. With each group of redraw
rod, after drawing, some wire coils were solution heat treated, then artificially aged or naturally
aged. The other wire coils were artificially aged or naturally aged without solution heat
treatment. Mechanical properties of the wires were assessed by a tensile testing machine (model
UTM-1000).
With suitable aging temperature and aging time, wires produced from each group of redraw
rod coils with or without solution heat treatment attain tensile requirements of ASTM B398, but
wires produced with solution heat treatment attain higher elongation than wires produced
without solution heat treatment.
Keywords: 6201 aluminum alloy, Aluminum alloy wire, Aluminum Alloy Conductor,
Aluminum alloy cable .
Classification numbers: 2.9.1, 2.10.2.
1. INTRODUCTION
Type 6201 aluminum alloy is a heat treatable one with high electrical conductivity and
good mechanical strength. It is widely used for the transmission and distribution of electricity
[1]. Type 6201 wires are used in production of AAAC (All Aluminum Alloy Conductor). A

comparison of the performance of the AAAC and conventional ACSR (Aluminum Conductor
Steel Reinforced) conductors, AAAC has lower power losses, excellent corrosion resistance, and
better resistance to abrasion, all without compromising either electrical conductivity or strength
and sag properties [2].
Type 6201 aluminum alloy wire is drawn from 6201 aluminum alloy redraw rod. The 6201
aluminum alloy redraw rod has been manufactured by various procedures consisting of separate
steps which include: DC casting, continuous casting and rolling rod on a Properzi or Secim mill.
Additional steps may include:


Huynh Cong Khanh

a) Immediate quenching after rolling, but before winding into 2 or 3-tonne coils. The rod
is then cold drawn to form wire, and the wire is artificially aged at a temperature
between 250 F (121.11 oC) and 450 F (232.22 oC) [3].
b) The 3/8 inch (9.65 mm) rod was drawn to 0.210÷0.211 inches (5.33÷5.35 mm) and
solution-treated in molten salt at 965 F (518 oC) for 20 min, quenched in cold water,
and followed by a rinse in tepid water. The T4 wire was drawn to finish gage and
artificially aged for 10 hours at 320 F (160 oC) to the T81 condition [4].
According to G. Davies [5], Chia supposes the continuous quenching and solution treatment
method (method a) saves cost, reduces in handling damage, and attains more uniform
mechanical properties of aluminum alloy redraw rod. Nicoud et al. think that more reliable
product which is easier to process can be achieved with separate solution treatment (method b).
Both methods (a) and (b) produce rod capable of being processed into wire to meet UK
specification BS 3242:1970.
Type 6201 aluminum alloy rod is also manufactured by extrusion press. In practice for
manufacturing of semi-finished products of low-ductile and low-tech alloys that are difficult to
deform in casting and rolling plants, one has to use discrete methods of pressing, making
products of limited length [6]. The reaction of the billet with the container and die results in high
compressive stress that is effective in reducing the cracking of the billet material during primary

breakdown from the billet. Extrusion is the best method for breaking down the casting structure
of the billet, since the billet is subjected only to compression [7]. In addition, when producing
rods by shape-rolling methods including production-on-casting and rolling mills the degrees of
reduction at one stage are so low in comparison to pressing that the number of mill stand and
passes during rolling (even on a continuous mill) is 15-20 or more [6].
For the production of coiled semifinished products for further processing, such as rod
drawing production, billet-on-billet is also a viable process. Billet-on-billet extrusion is a special
method for aluminum alloys that are easily welded together, at the extrusion temperature and
pressure, as 6000-series alloys. Using this process, the continuous length of semifinished
products can be produced by different methods [7].
Correct heat treatment of soft and medium grade aluminum alloy is important to obtain the
required mechanical properties. For all heat treatable aluminum alloys, heat treatment is a twostage process: solution heat treatment followed by precipitation hardening (aging). For 6000series alloys, the extrusion may be quenched directly from the extrusion temperature. Usually, a
forced-fan cooling system is sufficient, but water quenching is sometimes needed [7]. Therefore,
billet-on-billet extrusion permits producing press-quenched redraw rod. From that redraw rod,
6201 alloy wire is drawn and then subjected to artificial aging to meet required properties
without a separate solution quenching operation.
The aim of this work is to study the process of manufacturing 6201 aluminum alloy wire
from billet-on-billet extruded redraw rod of about 4.7 mm in diameter.
2. EXPERIMENTAL METHOD
Type 6201 aluminum alloy wire was manufactured from 4.7 mm diameter 6201 aluminum
alloy redraw rod coils. Redraw rod coils were manufactured by billet-on-billet extrusion on a
300 ton Cincinnati Milacron hydraulic extrusion press. The working parameter of billet
extrusion for production of redraw rod was as follows: pressing capacity: 300 tons; type of die:
feeder plate die with 14 exit holes of 4.8 mm each; extrusion speed: 15 m/min; billet
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Effects of heat treatment on the mechanical properties of 6201 aluminum alloy wire

temperature: 470 oC. The chemical composition of used 6201 alloy was analyzed by optical

emission spectrometer SPECTROLAB M12 and the result shown in Table 1. For metallographic
examination of as-cast used 6201 alloy, samples were prepared by using standard grinding
papers and were polished. Samples were then etched with 20% H3PO4 solution to study
microstructure using the optical microscope (OLYMPUS MPE3). As shown in Fig.1, the
microstructure of used 6201 alloy in the as-cast state consists of α-Al matrix and intermetallic
phases, as Mg2Si, Si, -Al8Fe2Si, -Al5FeSi in grain boundaries.
Table 1. Chemical composition (in wt%) of 6201 aluminum alloy.

Composition, %
Alloy
6201

Cu

Fe

Si

Mn

Mg

Zn

Cr

B

Ti

Al

0.048 0.314 0.832 0.010 0.601 0.005 0.002 0.0025 0.0183 Balance

Figure 1. The microstructure of used 6201 alloy in as-cast state (×100).

The redraw rod coils were divided into two groups:
1) Group A: The redraw rod coils were annealed at 480 oC for 4 hours in a chamber-type
electric resistance furnace, then redraw rod coils were taken out and air-cooled. After
annealing, the redraw rod coils were drawn from 4.7 mm to 2.7 mm in diameter. Some
samples of 2.7 mm wire were artificially aged at 170 oC with aging duration of 5, 6 or 7
hours or naturally aged (not artificially aged) for 5 days without solution heat
treatment. Other samples of 2.7 mm wire were solution heat treated at a temperature of
520 oC, followed by water quenching. The soaking time for solution heat treatment was
1 hour. Then the wire samples were artificially aged at 150, 160, and 170 oC for 5, 6,
and 7 hours, respectively.
2) Group B: The redraw rod coils were drawn from 4.7 mm to 2.7 mm in diameter
without annealing before drawing. Some samples of 2.7 mm wire were artificially aged
at 170 oC with aging times of 5, 6, 7, 8 hours and naturally aged for 5 days without

13


Huynh Cong Khanh

solution heat treatment. Other samples of 2.7 mm wire were solution heat treated at 520
o
C, followed by water quenching. The soaking time for the solution heat treatment was
1 hour, then the wire samples were artificially aged at 150 oC for 5, 6, 7 hours.
Finally, the samples of both groups were assessed for their mechanical properties by the

tensile testing machine (model UTM-1000). Tensile tests were conducted using 250 mm gauge
length samples according to ASTM B398. The number of samples used for tensile tests for each
state of Aluminum alloy wires was 2-3.
3. RESULTS AND DISCUSSION
Table 2 and Figure 2 show the mechanical properties of aluminum alloy wires drawn from
the annealed redraw rod. Wire samples were subjected to artificial aging at 170 oC for 5 hours
without solution heat treatment to achieve tensile strength and elongation according to the
requirements of ASTM B398 (≥ 315 MPa and ≥ 3.0 %). But, when keeping aging temperature at
170 oC and increasing aging time to 6 or 7 hours, the tensile strength of those wire samples
decreases to the lower requirements of ASTM B398.
Used alloy in this work has 0.601 % Mg, 0.832 % Si and 0.314 % Fe, so under equilibrium
solidification, the following equilibrium phases are possible: Mg2Si, Si, -Al8Fe2Si, -Al5FeSi
[8, 9]. Assuming that all Fe and Mg combine with Si and -Al5FeSi is the predominant phase
solution formed, the amounts of Mg2Si and excess Si can be calculated as follows [1]:
Mg (%) = %Mg + 1/1.73(%Mg) = 0.948 %
Excess Si (%) = %Si – [1/2(%Fe) + 1/1.73(%Mg)] = 0.328 %.
Therefore, according to Al-Mg2Si pseudobinary phase diagram [10], most Mg2Si phases
dissolve in the solid solution when redrawing rod coils were annealed at 480 oC for 4 hours.
While redrawing rod coils were cooled in air, some part of Mg2Si precipitated but nearly all
Mg2Si remained in the solid solution because, with a small diameter of redraw rod and a small
amount of magnesium and silicon, the alloy may be quenched in the air. Furthermore, excess Si
promotes an additional response to age hardening by both refining the size of the Mg2Si particles
and precipitating as Si. The addition of a small amount of Cu may lessen the adverse effect of
delay at room temperature by reducing the onset and rate of natural aging and promoting an
increased response to artificial aging. The addition of iron can refine grain structure and increase
the mechanical properties of Al-Mg-Si alloy [11, 12]. Deformation of supersaturated solid
solution causes partial precipitation and considerable effects on the precipitation during
subsequent heating. Cold deformation increases the precipitation process and changes
distribution characteristics of the second phase and its dispersion during aging [12]. As a result,
after annealing, drawing, and artificial aging at 170 oC for 5 hours, 6201 alloy samples (sample

A1) have high tensile strength and suitable elongation.
The age hardenable precipitation formation sequence in 6xxx alloy is as follows: α
supersaturated solid solution (SSS) → GP zones → β’’ → hexagonal β’ (Mg2Si) → fcc
β(Mg2Si). Precipitation of the alloying as coherent GP zones and coherent β’’ and hexagonal
coherent β’ (Mg2Si), during aging treatment, provides strengthening due to the presence of
coherency strain field around the precipitates, which interacts with the moving dislocation. The
equilibrium fcc β(Mg2Si) is incoherent and formation of incoherent equilibrium precipitates
culminates in a slight loss in hardness and strength due to the absence of lattice mismatch strain,
that is, coherency strain around the equilibrium precipitates in 6xxx alloys. Overaging of the fcc
β(Mg2Si) precipitates leads to coarsening of precipitates and results in a further loss in strength
14


Effects of heat treatment on the mechanical properties of 6201 aluminum alloy wire

[13, 14]. Therefore, with an increase of aging time to 6 or 7 hours at 170 oC, more incoherent
equilibrium fcc β(Mg2Si) phase is formed and coarsened due to overaging. Tensile strength is
also decreased.
With solution heat treatment at 520 oC followed by water quenching, Mg2Si phase dissolves
in the supersaturated solid solution. The high content of Mg and Si in supersaturated solid
solution results in a large number of precipitates during aging. A large amount of small and
uniformly distributed precipitates will appear, thus the mechanical properties of the materials
can be improved [15]. Siddiqui et al. showed that as the aging temperature and time increase, the
density of GP zone also increases [16].
Table 2. Mechanical properties of 2.7 mm diameter 6201 aluminum alloy wires drawn from annealed
redraw rod (The group A).
Sample
designation

Sample state

Average tensile
strength ± SD, 
(MPa)

Average
elongation in
250 mm ± SD,

(%)

A1

Annealed – Drawn - Artificially aged at
170 oC for 5 hours

340.46 ± 38.97

3.6 ± 0

A2

Annealed – Drawn - Artificially aged at
170 oC for 6 hours

250.57 ± 19.69

2.59 ± 0.20

A3

Annealed – Drawn - Artificially aged at
170 oC for 7 hours

263.53 ± 2.25

3.27 ± 0.31

A4

Annealed – Drawn - Naturally aged for
5 days

302.73 ± 10.10

3.39 ± 0.93

A5

Annealed – Drawn - Solution heat treated Artificially aged at 150 oC for 5 hours

282.13 ± 19.07

11.53 ± 3.06

A6

Annealed – Drawn - Solution heat treated Artificially aged at 150 oC for 6 hours

297.70 ± 17.15

9.47 ± 2.81

A7

Annealed – Drawn - Solution heat treated Artificially aged at 150 oC for 7 hours

298.17 ± 9.76

15.00 ± 2.25

A8

Annealed – Drawn - Solution heat treated Artificially aged at 160 oC for 5 hours

304.47 ± 16.95

12.80 ± 2.43

A9

Annealed – Drawn - Solution heat treated Artificially aged at 160 oC for 6 hours

326.8 ± 6.05

9.47 ± 1.40

A10

Annealed – Drawn - Solution heat treated Artificially aged at 160 oC for 7 hours

360.55 ± 22.70

8.80 ± 0.57

A11

Annealed – Drawn - Solution heat treated Artificially aged at 170 oC for 6 hours

243.15 ± 6.29

11.4 ± 1.41

A12

Annealed – Drawn - Solution heat treated Artificially aged at 170 oC for 15 hours

213.55 ± 12.09

11.00 ± 1.41

15


Tensile strength, MPa

Huynh Cong Khanh

400
350

300
250
200
4

6

8

10

12

14

16

Ageing times, h
Artificial ageing at 170oC (without solution heat treatment)
Artificial ageing at 150oC (with solution heat treatment)
Artificial ageing at 160oC (With solution heat treatment)
Artificial ageing at 170oC (With solution heat treatment)

Figure 2. Effect of aging temperature and aging time on the tensile strength of 6201 aluminum alloy wires
drawn from annealed redraw rod.

Figure 3. The force-displacement curves from tensile tests of samples A10.

Hence, the degree of irregularity in the lattices causes an increase in the mechanical
properties of Al-Mg-Si alloy [17]. As seen in Fig. 2, the tensile strength of wire samples

subjected to artificial aging at 160 oC is higher than the tensile strength of wire samples
subjected to artificial aging at 150 oC. Also, the tensile strength of samples subjected at 150 and
160 oC increases as aging time increases. However, the strength of samples subjected artificial
aging at 170 oC is lower than the strength of samples subjected to artificial aging at 150 and
160 oC due to overaging, thus precipitates agglomerate and coarsen into larger particles and
bigger grain size, causing fewer obstacles to the movement of dislocation [17]. Figure 3 shows
the force-displacement curves from tensile tests of samples A10 which attain the highest tensile
strength in group A. After artificial aging at 170 oC and natural aging for 5 days, wire samples
drawn from a second redraw rod coil group, without annealing before drawing and without
solution heat treatment, had high tensile strength. With an extruded billet temperature of 470 oC,
nearly all Mg2Si phase alloy dissolved in the solid solution, as seen in the Al-Mg2Si
pseudobinary phase diagram [10]. Type 6000-series alloys may be quenched at the extrusion
press when the product emerges hot from the die, thereby eliminating the need to solution treat

16


Effects of heat treatment on the mechanical properties of 6201 aluminum alloy wire

as a separate operation [7]. With a small diameter redraw rod (4.7 mm), an air quenching in the
press may be sufficient. Therefore, after extrusion, following drawing, and artificial aging at
170 oC or natural aging for 5 days, wire samples attain high tensile strength, as shown in Tab. 3
and Fig. 4. The elongation of those samples is low because, after cold drawing, tensile strength,
yield strength and hardness of redraw rod increase at the expense of ductility and formability
[11]. However, as aging time increases, tensile strength and elongation increase. Mechanical
properties of samples aged at 170 oC for 7 hours meet the requirements of ASTM B398 (tensile
strength  315 MPa, elongation of 250 mm  3.0 %). When artificial aging time increases to 8
hours, the mechanical properties of samples decrease due to overaging.
Table 3. Mechanical properties of 2.7 mm diameter 6201 aluminum alloy wires drawn from 4.7 mm
diameter non-annealed redraw rod (The group B).

Sample
designation

Sample state

Average tensile
strength ± SD, 
(MPa)

Average
elongation in 250
mm ± SD, (%)

B1

Non-annealed –Drawn - Artificially aged
at 170 oC for 5 hours

324.6 ± 45.24

2.67 ± 0.23

B2

Non-annealed - Drawn – Artificially aged
at 170 oC for 6 hours

364.47 ± 9.81

2.8 ± 0

B3

Non-annealed –Drawn - Artificially aged
at 170 oC for 7 hours

383.9 ± 12.68

3.47 ± 1.01

B4

Non-annealed - Drawn - Artificially aged
at 170 oC for 8 hours

316.05 ± 12.09

1.80 ± 0.28

B5

Non-annealed - Drawn – Naturally aged
for 5 days

360.97 ± 10.10

-

B6

Non-annealed - Drawn - Solution heat
treated - Artificially aged at 150 oC for 5
hours

307.00 ± 31.25

10.60 ± 0.28

B7

Non-annealed - Drawn - Solution heat
treated - Artificially aged at 150 oC for 6
hours

305.45 ± 9.69

8.00 ± 0.57

B8

Non-annealed - Drawn - Solution heat
treated - Artificially aged at 150 oC for 7
hours

342.35 ± 10.39

12.00 ± 0.57

Wire samples are drawn from non-annealed redraw rod, then solution heat treated and
artificially aged at 150 oC, have tensile strength lower than the tensile strength of wire samples

aged without solution heat treatment, but elongation of those samples is greater than the
elongation of samples aged without solution heat treatment. The reason for this is that the
recrystallization of deformed aluminum alloy appears at solution heat treatment temperature.
During recrystallization, the dislocation density will be reduced down to an equilibrium value. A
new microstructure with relative equilibrium defect density is formed and the alloy loses the
additional strength acquired in cold drawing at the increased ductility and formability. As
artificial aging time increase to 7 hours, the mechanical properties of those wire samples achieve

17


Huynh Cong Khanh

Tensile strength, MPa

the requirements of ASTM B398. Figure 5 shows the force-displacement curves from tensile
tests of samples B3 which attain the highest tensile strength in group B.
450
400
350
300
250
200
4

5

6

7

8

9

Ageing times, h
Artificial ageing at 170oC (without solution heat
treatment)
Artificial ageing at 150oC (with solution heat
treatment)
Figure 4. Effect of aging temperature and aging time on the tensile strength of 6201 aluminum
alloy wires drawn from non-annealed redraw rod.

Figure 5. The force-displacement curves from tensile tests of samples B3.

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Effects of heat treatment on the mechanical properties of 6201 aluminum alloy wire

4. CONCLUSION
With suitable aging temperature and aging time, wires drawn from annealed and nonannealed redraw rod, then artificially aged without solution heat treatment, can attain the tensile
requirements of ASTM B398 with high tensile strength, such as samples A1, B3. This is also the
advantage of the billet-on-billet extrusion method for production of small (4.7 mm diameter)
quenched redraw rod, and from that redraw rod, quality 6201 aluminum alloy wire can be
produced without a separate quenching solution operation.
With suitable aging temperature and aging time, wires drawn from annealed and nonannealed redraw rod, then solution heat treated with artificial aging, can attain the tensile
requirements of ASTM B398 with high tensile strength and high elongation of the wire, such as
samples A9, A10, B8.
Acknowledgments: The author gratefully acknowledges the financial support of Ho Chi Minh City

Department of Science and Technology.

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