Materials Sciences and Applications, 2011, 2, 469-475
doi:10.4236/msa.2011.25063 Published Online May 2011 (http://www.SciRP.org/journal/msa)
469
Melting and Corrosion Behavior of Al-9Zn Based
Alloys with Cu and Mg Additions
El Said Gouda1,2, Emad Ahmed1, NabihTawfik1
1Solid State Physics Department, Physics Division, National Research Center, Dokki, Giza, Egypt; 2Physics Department, Faculty of
Science, Jazan University, Jazan, Saudi Arabia.
Received May 1st, 2010; revised July 22nd, 2010; accepted May 11th, 2011.
ABSTRACT
In the present paper, the effect of Mg and Cu additions on melting, mechanical and corrosion behavior of Al-9Zn alloy
was studied and analyzed. It was found that, addition of Cu and Mg led to form the Al-Cu, Al-Mg and Mg-Zn interme-
tallic compounds. These compounds tend to increase the hardness values due to the precipitation strengthening har-
dening mechanism of these compounds. Also corrosion behavior of the Cu and Mg content alloys measured by the
weight loss method is better than those of the Al-9Zn alloy. Furthermore, corrosion resistance of the Cu content alloys
is superior to that of the Mg content alloys.
Keywords: Corrosion, Hardness, Melting Point, Aerospace Alloys
1. Introduction
The study of the material strength is an important subject
because it is the first characteristic comes in mind when
used in industrial applications specially that subjected to
shock loading. Steel is a good example for the most
strength materials, but its high density restricts its uses.
Recently, aluminum alloys are increasingly employed in
many important manufacturing areas, such as the auto-
mobile industry, aeronautics and the military [1]. Cur-
rently, it offers the greatest potential for cost effective
weight savings in automotive body structures and clo-
sures. With a density of only 33% of that of steel and a
greater strength-to-weight ratio, there is the possibility
for a weight savings of 40% to 50%. Also, Mg alloys are
very attractive materials for producing lightweight com-
ponents for automobiles because they have densities that
are 66% of Al alloys and 22% of steel. With their lower
density and moderate strength, Al-Mg alloys are well
suited for a number of applications, ranging from steer-
ing wheels and instrument panels to engine and transmis-
sion components. The mechanical properties of the Al-
Mg plastically processed alloys depend on the content of
magnesium in the alloy. With an increase of magnesium
from 0.5% to 5% the properties increase; this rise is
greater when magnesium increases from 3% to 6% [2].
There are many studies characterize the strength and
mechanical properties of Al-based and Mg-based alloys
with different elements [3-8]. The present paper aims to
characterize corrosion and mechanical properties of the
quaternary alloy Al-1.5Cu-9.5Zn-3Mg as an example for
a high strength material.
2. Experimental Procedures
Four alloys of chemical composition as illustrated in Ta-
ble 1 were prepared in the as-cast condition. The re-
quired quantities were weighted out and melted in an
electrical furnace then thermally agitated to ensure the
homogenization. The molten alloys were cast into gra-
phite molds to produce rods of 25 mm length and 10 mm
diameter. Then the rods were cut in to small discs of
about 1 cm length. X-ray diffraction analysis was per-
formed to identify the phases presented in these alloys
using a 1390 Philips X-ray Diffractometer with Cu-ra-
diation. DSC tests were carried out during heating using
a heating rate of 10˚C/min to evaluate the melting beha-
vior of these alloys. Corrosion behavior of these alloys
was determined chemically by the weight loss method.
The test pieces were cut into 1 × 1 cm and mechanically
polished with emery paper and weighted. Then the sam-
ples were suspended in a test solution of 1 mole of HCl
with doubly distilled water. The measurements were car-
ried out after suspension time of 15, 30, 45, 60 and 75
min. The average weight loss at the specific time was

Melting and Corrosion Behavior of Al-9Zn Based Alloys with Cu and Mg Additions 470
Table 1. Chemical composition of the used alloys.
Sample Chemical composition
alloy 1 Al-9Zn
alloy 2 Al-9Zn-1.5Cu
alloy 3 Al-9Zn-3Mg
alloy 4 Al-9Zn-1.5Cu-3Mg
calculated. Measurements of hardness were done using
Vickers hardness tester with the test samples placed
against a glass slide with a constant load of 4.9 N for 10
sec.
3. Results and Discussion
3.1. Phases Constitution
Figure 1 shows the X-ray diffraction patterns of the Al-
9Zn, Al-9Zn-1.5Cu, Al-9Zn-3Mg, Al-9Zn-1.5Cu-3Mg
alloys. All diffraction patterns contain peaks due to Al
matrix phase. Accordingly, the Al-9Zn alloy shows the
presence of only the Al phase, suggesting that all the Zn
content has gone in to Al to form supersaturated solid
solution. This is inferred from the shift of Al peaks to
higher angular positions and consequently the Al solid
solution phase had smaller lattice parameters than that of
pure Al. The pattern of the Al-9Zn-1.5Cu alloy indicates
two X-ray diffraction peaks at 2θ ≈ 43.25 and 43.96˚
refer to the AlCu4 and Al4Cu9 compounds, respectively.
The pattern of the Al-9Zn-3Mg alloy indicates precipita-
tion of Al2Mg compound at 2θ ≈ 36.9, 39.13 and 43.26˚,
and MgZn2 compound at 2θ ≈ 45.18˚. This means adding
of Mg decrease the solubility of Zn in Al matrix phase by
forming the MgZn2 compound. The quaternary Al-9Zn-
1.5Cu-3Mg alloy indicates precipitations of Al12Mg17,
MgZn2, Al2Mg and Al4Cu9 compounds as illustrated in
Table 2. Increasing the amount of the intermetallic
compound MgZn2 indicates that, the solubility of Zn in
Al-matrix was decreased.
3.2. Melting Behavior
DSC endothermic peaks of the Al-9Zn, Al-9Zn-1.5Cu,
Al-9Zn-3Mg, Al-9Zn-1.5Cu-3Mg alloys during conti-
nuous heating are demonstrated in Figure 2. It shows
that, the DSC curve is not discernible exothermic/endo-
thermic peaks occurred until the remelting temperature
range was reached. In alloy 1 there is a large endothermic
peak at 657.7˚C, corresponds to the melting reaction of the
binary Al-9Zn alloy. DSC curve of alloy 2 consists of
three endothermic peaks, as labeled 1, 2 and 3, respective-
ly. Peak 1 is the smallest one with an onset temperature of
about 532.7˚C followed by the second peak. Peak 2 ap-
peared at 640.3˚C, while the third peak, peak 3 started at
Table 2. Intermetallic compounds presented in Al-Zn-Cu-
Mg alloys.
Alloy Lattice parameter, a of
Al matrix phase, Å
Intermetallic
compound 2θ degree
alloy 14.050 - -
alloy 24.044 AlCu4
Al4Cu9
43.25
43.96
alloy 34.063
Al2Mg
MgZn2
36.95
39.13
43.26
45.18
alloy 44.059
Al2Mg
Al12Mg17
MgZn2
Al4Cu9
37.33
40.52
39.66
65.15
41.25
45.73
43.75
677.5˚C and a peak temperature of about 697.8˚C. DSC
curve of alloy 3 indicates a single endothermic peak due
to the melting reaction observed at 643.44˚C. While, the
DSC curve of alloy 4 indicates two endothermic sharp
peaks, the first, which is the smallest one is observed at a
temperature of about 480.5˚C, which may corresponding
to the diffusion mechanism of low melting Al12Mg17
compound formed at this alloy composition. While, the
second peak which is the largest one observed at a tem-
perature of about 634.7˚C is related to the melting reac-
tion of this alloy.
3.3. Hardness
In solid mechanics, the material hardness is described as
the resistance of deformation and should be independent
from the applied load. So, it was measured using a fixed
load of 4.9 N for 10 sec and the results are illustrated in
Figure 3. It was observed that, the hardness with the
corresponding values of the yield strength [9] is in-
creased continually with the Cu or Mg content alloys.
The maximum value obtained for alloy 4, can be attri-
buted to the more precipitations of Al-Cu, Al-Mg and
Mg-Zn IMCs, which act as hard inclusions in soft matrix.
The continuous increase of Hv can be attributed to the
precipitation hardening strengthening mechanisms of
Al-Mg and Al-Cu and Mg-Zn compounds.
3.4. Corrosion Behavior
Corrosion behavior of metals in an aqueous environment
is characterized by the extent to which it dissolves in the
solution. This can be quantified using the relationship
W0= WB − WA, W0; weight lost in test solution, WB;
weight before exposure, WA; weight after exposure. Fig-
ure 4 shows weight loss of the samples versus the expo-
sure time in min. It shows that, the weight loss increases
as the exposure time increases by different amounts de-

Melting and Corrosion Behavior of Al-9Zn Based Alloys with Cu and Mg Additions 471

Melting and Corrosion Behavior of Al-9Zn Based Alloys with Cu and Mg Additions 472
Figure 1. X-ray diffraction pattern of Al-9Zn, Al-9Zn-1.5Cu, Al-9Zn-3Mg and Al-9Zn-1.5Cu-3Mg alloys.

Melting and Corrosion Behavior of Al-9Zn Based Alloys with Cu and Mg Additions 473
Figure 2. DSC endothermic peak of Al-9Zn, Al-9Zn-1.5Cu, Al-9Zn- 3Mg and Al-9Zn-1.5Cu-3Mg alloys.
Figure 3. Hardness with the corresponding values of the yield strength of Al-Zn-Cu-Mg alloys.

Melting and Corrosion Behavior of Al-9Zn Based Alloys with Cu and Mg Additions 474
Figure 4. Corrosion behavior of Al-Zn-Cu-Mg alloys.
pends on the alloy composition. The maximum value of
the weight loss is obtained for the Al-9Zn alloy. All ad-
ditions to this alloy decrease the weight lost per unit area
than that of the binary alloy and the minimum value is
obtained in the Al-9Zn-1.5Cu alloy. This behavior can be
attributed to the presence of Al-Cu, Al-Mg and Mg-Zn
compounds, which might act as a high corrosion resis-
tance compounds.
4. Conclusions
The effect of 1.5 Cu and 3 Mg as third and quaternary
additions to the Al-9Zn alloy on structure, melting reac-
tion, corrosion behavior and mechanical properties were
studied and analyzed using X-ray diffraction, DSC tests,
weight loss system and Vickers micro hardness tester,
respectively. It was found that, adding of Cu and Mg led
to precipitation of Al-Cu, Al-Mg and Mg-Zn compounds.
These compounds led to increase the Vickers hardness
number and corrosion resistance. Furthermore, corrosion
resistance of the Cu-content alloys is superior to that of
the Mg content alloy, which concluded that the Al-Cu
compound is a more corrosion resistance than the Al-Mg
or Mg-Zn compounds.
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