Journal of Minerals and Materials Characterization and Engineering, 2012, 11, 1020-1026
Published Online October 2012 (http://www.SciRP.org/journal/jmmce)
Mechanical Properties and Microstructures of L ocally
Produced Aluminium-Bronze Alloy
Uyime Donatus1, Joseph Ajibade Omotoyinbo1, Itopa Monday Momoh1,2
1Department of Metallurgical and Materials Engineering, Federal University of Technology, Akure, Nigeria
2Engineering Materials Development Institute, Akure, Nigeria
Received June 4, 2012; revised July 12, 2012; accepted July 24, 2012
ABSTRACT
This work studied the feasibility of producing a dual-phase aluminium bronze alloy and the use of selected treatments to
manipulate the mechanical properties of the produced alloy using local techniques, as a potential replacement for con-
ventional structural materials, particularly steels. Sand casting was used and was found to be effective based on its ad-
vantages of low cost, ease of use and flexibility in the production of a dual-phase aluminium bronze alloy with
pre-selected composition of 11% Al content. Cold deformation of 10 and 20% degrees and selected heat treatments
were used on the cast alloy to influence its mechanical properties. The selected heat treatments are solution heat treat-
ment, normalising, and ageing. The results showed that normalising gave the optimum mix of tested mechanical proper-
ties with ultimate tensile strength in the range of 325 MPa, elongation of around 60% and Rockwell hardness values of
46.5 - 63.7 HRc, making this alloy suitable as alternatives to steel in low/medium strength structural applications.
Keywords: Aluminium-Bronze; Solution Heat Treatment; Dual-Phase; Cold Deformation
1. Introduction
Aluminium bronzes are copper based alloys with alu-
minium as the major alloying element usually in the
range 5% - 14% compositionally in the alloy, other alloy-
ing elements sometimes intentionally introduced are iron,
nickel, manganese, silicon and tin depending on the in-
tended application of the aluminium bronze.
Aluminium bronzes give a mix of a chemo-mechani-
cal properties superseding many other alloy series. These
make them to be most preferred particularly for demand-
ing applications [1]. “Aluminium bronzes are most val-
ued for their high strength and corrosion resistance in a
wide range of aggressive media” [2]. “They are most
commonly used in applications where their resistance to
corrosion makes them preferable to other engineering
materials. Another notable property of aluminium bronzes
are their biostatic effects. The basic properties of copper
alloys are largely influenced by copper itself” [3]. The
copper component of the alloy prevents colonization of
marine organisms including algae, lichens, barnacles and
mussels, and therefore can be preferable to stainless steel
or other non-cupric alloys in applications where such co-
lonization would be unwanted.
Besides their strength, toughness, corrosion resistance
in a wide range of aggressive media, wear resistance, low
magnetic permeability, non-sparking characteristics, alu-
minium-bronzes can be readily cast, fabricated, and ma-
chined. They can also be readily welded in either cast or
wrought form [4,5].
In spite of these wonderful attributes posed by alu-
minium bronzes, it is surprising to know that not much
work have been done on aluminium bronzes in Africa
especially in Nigeria. Structural applications are mostly
based on ferrous materials, steels in particular. Findings
have shown that aluminium bronzes are fast replacing
contemporary steel materials for some specific applica-
tions especially in components for marine/sub-sea appli-
cations. The consumption of aluminium bronzes have
increased sharply in the USA. And other countries due to
their property of being non-rusting in marine environ-
ment as well as also their resistance to corrosion in high-
ly aggressive environments. Aluminium bronze alloy
construction for basic oxygen and electric arc furnace
hoods, roofs and side vents was identified as a viable
alternative for carbon steel construction for these equip-
ments. The use of aluminium alloy was found to be as
much as five times the life of comparable carbon steel [6].
Manganese-nickel-aluminium-bronze (Aqualloy), for ex-
ample, was found to be more efficient than stainless steel
in making propellers. Nickel-aluminium bronzes have
greater resistance to cavitation erosion than cast steel,
Monel alloys and the 400 and 300 series of stainless
steels, that is why it is suitable for propellers, pump im-
pellers and casings and turbine runners giving them long

U. DONATUS ET AL. 1021
service lives and operating efficiency [7]. Aluminium
bronze wire is almost as strong as good steel wire and
castings made from it are almost as hard as steely iron
[8].
There are various categorizations of aluminium bronzes,
90% of them by different authors and bodies do not leave
out the duplex phase group of aluminium bronzes which
is the primary focus of this research. The dual (duplex)
phase represents the highest tonnage and most alloyed of
the aluminium bronzes, containing 8% - 11% aluminium
and usually with the additions of iron and nickel for
higher strength [9] and for prevention or delay of β solid
solution decomposition to the (α + γ2) eutectoid, γ2 is un-
desirable and causes brittleness; slow cooling brittleness-
3% iron and 3% nickel were considered most suitable
[10]. This dual phase aluminium bronzes can be worked
or heat treated to obtain optimal strength and ductility
[11]. During equilibrium cooling of aluminium bronze
alloy with 10% aluminium, α-aluminium bronze precipi-
tates from β-aluminium bronze phases below 930˚C [12].
In marine environment, the requirements for marine
component are, among others, high strength to weight
ratio, good castability, and tolerance of local working for
repairing damage sustained during service which narrow
our choice of alloy to aluminium bronzes. Which thus
serves as our basis for this research work: to develop a (α
+ β)/(α + γ2) phase aluminium bronze with a view to
seeking replacement for conventionally used components
that fail readily during service.
2. Materials and Equipments
Copper coils, aluminium scraps, weighing balance, pit
furnace, rolling machine, vernier calliper, bench vice,
student lathe machine, grinding and polishing machine,
hack-saw, muffle furnace, metallurgical microscope, di-
gital Rockwell tester, Mosanto tensometer.
2.1. Experimental Procedures
2.1.1. Production
1 m long and 10 mm in diameter aluminium bronze rods
of composition as given in Table 1 were produced via
sand casting by dissolving a measured amount of the
aluminium piece in a measured molten copper in a fired
pit furnace, stirred and cast. The chemical analysis of the
produced aluminium bronze alloy was evaluated using a
mass spectrometer. The cast aluminium bronze rods
where subjected to 10% and 20% cold deformation using
a miniature rolling machine.
2.1.2. Hea t Treatment
The deformed rods where then subjected to selected
forms of heat treatment: annealing, quenching (solution
heat treatment), normalizing and ageing using a muffle
Table 1. Chemical composition of aluminium bronze deve-
loped.
Element % Weight
Cu 89.0764
Al 10.8230
Si 0.0495
Fe 0.0242
Mg 0.0150
Zn 0.0019
furnace. The normalising (heating to 250˚C and cooling
in air) and ageing (heating to 160˚C and 180˚C, held for
6 hours and then cooled in water at room temperature)
were done on prior annealed and solution heat treated
samples. Annealing was done on prior deformed rods by
heating to 750˚C and holding for 2 hours followed by
cooling in the furnace while solution heat treatment was
carried out by heating the samples to 900˚C and holding
for 15 minutes before cooling in chilled water. Several
samples were selected per treatment.
2.1.3. Tensile and Hardness Test
The heat treated rods where then machined to tensile
standard configuration test which was conducted in a
Mosanto Tensometer. The dimension used is as shown in
Figure 1. The hardness tests were carried out on a Digi-
tal Rockwell Tester by applying a force of 60 Kgf (about
588N). Prior to this, the specimens were grinded to a flat
surface using an emery paper of varios grits (between 60
to 180 micron)
2.1.4. Mi cro-Exam i nation
A daheng software driven optical microscope was used
to analyzed the microstructures of the developed alloy.
Prior to this, the specimen for the microscopy were
mounted, grinded using a series of emery paper of grits
sizes ranging from 60 µm - 2400 µm, it was further pol-
ished using an ultrafine polishing cloth, its effectiveness
was enhanced using polycrystalline diamond suspension
of particle size 3 µm with ethanol solvent. The specimen
was chemically etched by swabbing using acidified ferric
chloride composing of 8 g of Ferric (II) Chloride, 50mil
of HCl and 100 mil of water for 60seconds before micro-
structural examination was performed using optical mi-
croscope.
3. Results and Discussion
3.1. Castin g
Despite the difficulties encountered that would have be a
barrier in the course of casting, sand casting was selected
as a the best means of casting locally based on the avail-
able materials, low cost and flexibility; it was found ef-

U. DONATUS ET AL. 1022
5.0
55
37
10
Figure 1. A sketch of standard tensile specimen (all dimen-
sions in mm) [13].
fective as a sound golden yellow dual-phase aluminium
bronze alloy with a density of 7.74 g/cm3 and composi-
tion as shown in Table 1 was produced.
3.2. Mechanical Properties of As-Cast
Aluminium Bronze Alloy Produced
The mechanical properties of the as-cast aluminium
bronze sample with 0% deformation and no heat treat-
ment are as shown in Figure 2(a) with its ultimate ten-
sile strength being 230.4 MPa (low), very high hardness
of 38.4Rc and low ductility of 11.2% elongation. This
could be attributed to the presence of sparse distribution
of suspected α precipitates in a predominant β’ matrix
which has high strength (hardness) and low ductility [14]
as can be seen in its microstructure in Plate 1. However,
this is not to say that this as-cast structure cannot be used
for some important engineering applications where loads
of magnitudes in the range of one-third of its UTS are
being used.
3.3. Effect of Solution Heat Treatment on the
Mechanical Properties of Aluminium Bronze
This treatment significantly improved the tensile proper-
ties of this alloy (Figure 2(b)) particularly in the 20%
deformation sample as compared to the as-cast structure
though with significant reduction in hardness. This was
probably due to the transformation of the β’-phase pre-
sent in the ascast structure to produce structures of alu-
minium bronze pearlite (α + γ2) in a matrix of α domi-
nance, this structure has no clear area of stress concentra-
tion but rather has lamellar or alternate layers of γ2 and α
with the latter predominating the structure. See Plates 2
and 3. The soft α phase, serving as the major matrix for
the aluminium bronze pearlite, possibly brought about
the improved tensile strength and ductility with signify-
cant reduction in hardness strength.
3.4. Effect of Normalising on the Mechanical
Properties of Solution Heat Treated
Aluminium Bronze
This produced more improved mechanical properties
with the tensile strengths of both the 10 and 20% degrees
of deformation (Figure 2(c))exceeding that of the SHT
slightly and clearly higher than that of the as-cast struc-
ture, the hardness value for the 10% deformation sam-
ple was clearly greater than that of the SHT while that of
the 20% degree of deformation ironically dropped below
that of the SHT, but dropped far below that of the as-cast
structure in both cases. The ductility as a measure of %
elongation was significantly higher as compared to the as
cast structure but just slightly greater than that of the
SHT. The micrograph for the 10% degree of deformation
(Plate 4), shows more dispersed precipitates of α in a
more refined β’ matrix with finer grain structure, more
than that evident in that of the as-cast structure. The
pearlite structure in the SHT has been altered, with the
lamellar structure transforming to give β’ with more pre-
cipitates of α (as compared to the as-cast structure) pre-
cipitating out from the β’ phase into the same matrix with
more of it at the grain boundaries and with no undesir-
able γ2 phase, at all, which has deleterious effect on me-
chanical properties of aluminium bronze according to
literatures. This probably produced the improved proper-
ties effect as compared to the SHT and as-cast structure
except for the reduction in hardness strength when com-
pared to that of the as-cast structure particularly. The
micrographs of the 20% degree of deformation (Plate 5),
however, show that the structure is entirely an alumin-
ium-bronze pearlite plus γ2 structure with the later being
predominant, the presence of the aluminium bronze pear-
lite possibly accounted for the contrasting decline in its
hardness value as compared to that of the SHT and
as-cast structure.
3.5. Effect of Ageing on the Mechanical
Properties of Solution Heat Treated
Aluminium Bronze
Improved UTS in all cases (Figures 2(d) and (e))particu-
larly as compared to the control specimen with the ex-
ception of N and SHT (20% deformation) reduced hard-
ness values in AG1 and AG2(10% deformation) as com-
pared to the control, SHT and N but AG2 (20% deforma-
tion) showed improved hardness value only as compared
to SHT, increased ductility in AG1(10% deformation)
and AG2(20% deformation) as shown in figures 2(d)
and (e) respectively—when compared to SHT, C and N;
but reduced in AG1 and AG2 (both of 20% deformation)
only as compared to SHT and N. Ageing the alloy sur-
prisingly produced enlarged plates of the α+γ2 aluminium
bronze pearlite particularly for 20% deformation-180˚C
samples (Plate 9), but spread over patches of possible
kappa in α matrix for the 160˚C samples (Plates 6 and 7)
with fluctuating mechanical properties though never at
any instant equal to or lesser than the mechanic- cal
properties of the as-cast structure except for the hardness.
It should also be noted that ageing at 180˚C for 6 hours
after 20% cold deformation and SHT gave the highest

U. DONATUS ET AL. 1023
(a) (b)
(c) (d)
(e)
Figure 2. (a) Stress-Strain curve of as-cast Al-bronze sample (control-C); (b) Stress-Strain curve of cast Al-bronze subjected
to cold deformation followed by solution heat treatment; (c) Stress-Strain curve of cast Al- bronze subjected to cold defor-
mation followed by normalizing; (d) Stress-Strain curve of cast Al-bronze subjected to cold deformation followed by ageing
at 160˚C for 6 hours after solution heat treatment; (e) Stress-Strain curve of cast Al-bronze subjected to cold deformation
followed by ageing at 1800C for 6 hours after solution heat treatment.

U. DONATUS ET AL. 1024
Mag.x400
Plate 1. Microstructure of as-cast Aluminium bronze sam-
ple.
Mag.x400
Plate 2. Microstructure of cast Al-Bronze sample subjected
to 10% cold deformation followed by SHT.
Mag.x400
Plate 3. Microstructure of cast Al-Bronze subjected to 20%
cold deformation followed by SHT.
Mag.x400
Plate 4. Microstructure of cast Al-bronze sample subjected
to 10% deformation followed by SHT and Normalising.
Mag.x400
Plate 5. Microstructure of cast Al-bronze sample subjected
to 20% deformation followed by SHT and Normalising.
Mag.x400
Plate 6. Microstructure of cast Al-Bronze sample subjected
to 10% deformation followed by SHT and ageing at 160˚C
for 6 hours.

U. DONATUS ET AL. 1025
Mag. x400
Plate 7. Microstructure of cast Al-Bronze sample subjected
to 20% deformation followed by SHT and ageing at 160˚C
for 6 hours.
Ma
g
.x400
Plate 8. Microstructure of cast Al-Bronze sample subjected
to 10% deformation followed by SHT and ageing at 180˚C
for 6 hours.
Mag.x400
Plate 9. Microstructure of cast Al-Bronze sample subjected
to 20% deformation followed by SHT and ageing at 180˚C
for 6 hours.
Table 2. Sumarry of the mechanical properties of the de-
veloped aluminium bronze alloy.
Proof stress
(0.5%e, MPa)UTS (MPa) Hardness (HRc)
Elongation
(%)
Treatments
10%20%10%20% 10% 20% 10%20%
C 169 230.4 38.4 11.2
SHT 125185267.2321.8 49.8 51.3 53.458.7
N 165175327.9322.4 63.7 46.5 60.960.7
AG1 85 102320.0301.0 45.4 44.0 76.338.4
AG2 148173266.3329.6 39.9 53.4 43.568.8
Key: C = as cast Al-Bronze sample with 0% deformation and no treatment,
SHT = Solution Heat Treated samples (heated to 900˚C followed by quen-
ching in chilled water), N = Samples normalised at 250˚C for 20 minutes
after SHT, AG1 = Samples aged at 160˚C for 6 hours after SHT, AG2 =
Samples aged at 180˚C for 6 hours after SHT.
value of tensile strength, good ductility as shown in Ta-
ble 2—probably because of the enlarged alternate plates
of the α+γ2 in the entire pearlitic structure, {though rela-
tively low at the sample subjected to 10% deformation
(Plate 8)}—and fair enough hardness value which was
only lower than that of the ascast structure and the 10%
degree of deformation samples normalised after SHT.
4. Conclusion
This research work has shown that aluminium bronze
alloys with improved mechanical properties and micro-
structures as compared to conventionally used structural
alloys can be produced locally. Sand casting was found
effective-base on its advantages of low cost, ease of use
and flexibility-in the local production of the dual-phase
aluminium bronze with carefully selected composition of
11% Al content. Of the selected heat treatments-after
cold deformation of 10% and 20% degrees are: solution
heat treatment (heating the cast alloy to 900˚C and quen-
ching in chilled water); normalising (heating some of the
solution heat treated samples to 250˚C soaking for 20
minutes and cooling in air); and ageing (heating some of
the solution heat treated samples to 160˚C and 180˚C
respectively and held for 6 hours at these temperatures
before cooling in water), normalising gave the optimum
mix of tested mechanical properties with ultimate tensile
strength in the range of 325MPa, elongation of around
60% and Rockwell hardness values of 46.5 - 63.7 HRc,
making this alloy suitable as alternatives for low/medium
strength level applications.
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U. DONATUS ET AL. 1026
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