effect of scandium addition on the mechanical and

Book Chapter

Z. Ahmad, Abdul-Aleem and Anwar Ul-Hamid (2004) Effect of scandium addition on the mechanical and corrosion behavior of Al-Mg alloys, in Trends in Electrochemistry and Corrosion at the beginning of the 21st Century, Editors E. Brillas and P. L. Cabot, Published by University of Barcelona, Barcelona, Spain, 2004. pp. 1069-1081. ISBN: 84-475-2639-9

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EFFECT OF SCANDIUM ADDITION ON THE MECHANICAL AND CORROSION BEHAVIOR OF Al-Mg ALLOYS Zaki Ahmad1 Abdul Aleem, B.J.2 Anwarul Hamid3 Abstract The effect of scandium addition (0.1 to 0.9%) on the mechanical, microstructural and corrosion resistance of Al-2.5 Mg alloys has been investigated. Strength levels upto (322 MPa UTS and 242 MPa y can be achieved by alloying with 0.3% Sc with 0.14% Zr. Scandium contents higher than 0.6% do not appreciately contribute to strengthening of the alloy. The responsible precipitate for strengthening is Al3Sc which is very small ( 0.15 mm) and pins down the grain boundaries. Scandium added Al-2.5 Mg alloy show a good resistance to corrosion in 3.5% NaCl and exhibits a strong tendency to form protective films of boehmite. The corrosion resistance is not impaired by age-hardening. Because of their attractive contribution to mechanical properties and corrosion resistance, they are a strong competitors for applications requiring high performance alloys. Key Words: corrosion, mechanical behavior, microstructure, Al3Sc3 intermetallic, polarization.

Introduction Scandium is a novel alloying element for aluminum is mined and processed in Ukraine. It found major applications in Russian MIG 29 fighters planes because of the technical advantages it offered over other competitive alloys. Alloying with scandium has a strong influence on the structure and properties of aluminum and aluminum alloys [1-4]. The alloying addition of scandium is reported to be more effective than the addition of transition metals such as manganese, chromium or zirconium [5]. Several efforts have been made in the past to lower the density of Al-Mg alloys to the level of Al 7075 and elevate the strength to the levels of precipitation hardening alloys. Althoough Al-Mg alloys with a substantially high magnesium content (10%) approached the strength of precipitation hardened alloys [6, 7] they produced enormous processing difficulties and exhibited stress corrosion cracking [8]. This difficulty was overcome by using scandium as an alloying element in smaller concentrations. Scandium combines with aluminum in a spherical configuration which stabilizes the structure and pushes the strength of Al-Mg-Sc alloys to the level of precipitation hardened alloy. The Al3Sc(L12) phase forms a fine dispersion of spherical particles which provide a substantial increase in strength. Scandium reinforced aluminum alloys exhibit a high degree of grain refinement and weld strengthening, a high resistance to hot cracking in welds and inhibition of re-crystallization temperature up to 600oC [9]. Addition of zirconium ( 0.15%) leads to improvement of the strength of Al-Mg-Sc alloys with a lower scandium content [5]. Scandium added aluminum alloys have attracted considerable attention in the last decade [10-11] because of their attractive combination of properties. Whereas substantial progress has been made on the structural and mechanical characteristics of Al-Mg-Sc alloys, sufficient progress has not been achieved in comprehensively understanding their corrosion behaviour and only limited studies 1

Mechanical Engineering Department, King Fahd University of Petroleum & Minerals,, Dhahran, Saudi Arabia. Mechanical Engineering Department, King Fahd University of Petroleum and Minerals, Dhahran, Saudi Arabia. 3 Research Institute, King Fahd University of Petroleum & Minerals, Dhahran, Saudi Arabia. 2

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have been made [12-15]. A full knowledge of the corrosion behavior of Al-Mg-Sc is essential to determine its application potential in a wide spectrum of environment. It is the objective of this work to determine the corrosion behavior of Al-Mg-Sc alloys containing (0.1 to 0.9 wt % Sc) in 3.5 wt % NaCl. Limited studies on their mechanical properties have also been made.

2.0 EXPERIMENTAL METHODS Aluminum alloys 5052 with 0.1, 0.15, 0.3, 0.6 and 0.9 wt% scandium addition were made by induction melting in a re-crystallized alumina crucible under an argon atmosphere. Alloying with scandium powder was achieved in accordance with the guidelines of light Aluminum Metall, Germany. The scandium powder was covered by a foil of pure aluminum to protect it from air contact and dipped in a melt covered by argon. The alloy was chill cast in copper mold. Strips of 2 mm thickness were obtained from the ingots by an extrusion process. The chemical composition of the alloys is given in Table 1.0. Table 1.0. Chemical composition. of Al-Mg-Sc alloys. Alloy Desig- nation Si & Name 1 0.087 Al-Mg-Zr0.0-Sc0.0 2 0.11 Al-Mg-Zr0.14-Sc0.0 3 0.08 Al-Mg-Zr0.14-Sc0.15 4 0.09 Al-Mg-Zr0.14-Sc0.30 5 0.10 Al-Mg-Zr0.14-Sc0.60 6 0.092 Al-Mg-Zr0.14-Sc0.90

Fe

Cu

Mn

Mg

Cr

Zn

Ti

Zr

Sc

0.166

0.002

0.003

2.96

0.002

0.0025

0.03

-

-

0.153

0.002

0.002

2.9

0.0014

0.001

0.023

0.14

-

0.16

0.002 0.0032

2.97

0.0014

0.006

0.024

0.14

0.16

0.15

0.002

0.003

2.95

0.0013

0.010

0.024

0.14

0.29

0.16

0.002

0.003

2.96

0.001

0.002

0.021

0.14

0.62

0.160

0.003

0.004

2.87

0.001

0.007

0.028

0.14

0.91

2.0 SPECIMEN PREPARATION Specimen measuring 15 mm in diameter were used for electrochemical investigations and weight loss studies. They were polished with 320, 400 and 600 m SiC paper using de-mineralized water as lubricant. Final polishing was done with a 6 m diamond paste. The specimen were washed with de-mineralized water rinsed with acetone and dried 12 h before use. 3.0 EXPERIMENTAL PROCEDURE The rate of corrosion of the specimen was determined in accordance with ASTM G-31-72 Practice[16]. Specimen in triplicate were used. The corroded specimen were treated with a mixture of Cr2O3 and H3PO4 at 80oC to remove corrosion products. All specimens were treated separately in boiling benzene for five minutes and ethanol at 35oC and 5% acetic acid at 48o. 3.1 Electrochemical Measurement Tafel extrapolation and polarization resistance techniques were used to determine the corrosion behavior of experimental alloys.

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3.1-1 Tafel Plots The specimens were immersed in the test solution for two hours prior to commencement of polarization. The polarization was commenced from the corrosion potential (Ecor) firstly in the cathodic direction up to – 1300 mVSCE and to -400 mVSCF in the anodic direction. The scanning rate was maintained at 1.0 mV/min. The microprocessor fitted with a potentiostat examined the data on both the anodic and cathodic sites to find a straight line segment that would yield a Tafel constant. A software CMS100 was used to obtain the plots and electrochemical parameters. Corrosion rates are computed by input of a, c, Ecorr and Icorr value in the units of mils per year or millimeter per year. The measurements were made in accordance with ASTM specification G5-87 [17]. 3.1-2 Polarization Resistance The specimen was immersed in sea water for forty five minutes prior to commencement of polarization. The experiments were performed by a applying a controlled potential scan over a small range of potential (± 25 mVSCE) with respect to corrosion potential. A scanning rate of 1.0 mV/min was used. The slope of the potential current function at Ecorr was used with Tafel constant. a, c to determine Icorr (corrosion current) and hence the rate of corrosion [18]. 3.2 Mechanical Testing Tensile testing on the specimen were performed on an Instron (Instron Co. England) 1114 hydraulic machine. All tests were carried out in accordance with ASTM procedure. Tensile properties were calculated from the load versus displacement plots. Standard specimen dimensions were used. 3.3 Microstructure The microstructural studies were conducted by a low vacuum scanning electron microscope (LV-SEM). A microanalysis system with a Quant mapping software package for x-ray mapping was used for energy dispersion studies. 4.0 RESULTS AND DISCUSSION 4.1 Microstructure The phase diagram (Figure 1) shows that Al-SiC alloy is slightly hypereutectic and a very small amount of Al3Sc could be formed prior to solidification of Al phase. Alloys containing scandium addition show rectangular white precipitates whereas alloy not containing Sc show round white precipitates. SEM image of alloy 3 containing 0.6 wt% Sc shows distinct white rectangular precipitates enriched in scandium, (Figure 2) whereas the small white precipitate mainly show Mg, Fe and silicon as shown by EDS spectra, (Figures 3 and 4). The distribution of Al3Sc precipitate on grain boundaries is shown in TEM micrograph, (Figure 5). The Al3Sc precipitate was identified by EDS studies.

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Fig. 1. Al-Sc phase diagram.

Fig. 2. SEM image of Al-Mg-Zr-Sc alloy (age hardened) 300x.

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Fig. 3. EDS spectra of the small white rectangular precipitates.

Fig. 4. EDS spectra of white rectangular precipitate.

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Fig. 5. TEM microstructure showing Al3SiC precipitates and dislocation at the grain boundaries. Dislocation at the grain boundaries can also be observed in Figure 5. It is difficult to resolve Al3Sc precipitate because of the very small size ( 15-25 m) [14]. The Al3Sc coherent precipitates, appear to pin down the grain boundaries and substantially contribute the strengthening of the alloy (Fig. 5). The dislocation generation is also pre-dominant as observed in TEM micrograph. 4.2 Mechanical Behaviour The mechanical properties of the experimental Al-Mg-Sc alloys are shown in Table 2 and Figure 6. The lowest value of 0.2% yield strength and UTS are exhibited by alloy 1. That zirconium is a strengther is shown by the increase in the yield strength of alloy 1 (without Zirconium and Scandium) from 58 MPa to 110 MPa by addition of 0.14 wt% Scandium. Scandium addition acts synergistically with zirconium and enhance the yield strength as shown by alloys 3 and 4. The yield strength of alloy 3 doubles on increasing the scandium content from 0.16 (alloy 3) to 0.29% (alloy 4) with a significant increase in UTS. No significant increase in the yield strength is observed on increasing the scandium content from 0.29% to 0.9%. On the other hand, the yield strength is slightly lowered by addition of 0.9% scandium compared to addition of 0.6%. From previous works by Russians, it was established that the maximum amount of useful Sc addition was 0.6% [19], although addition up to 1.0 wt% scandium have been made to Al and Al-Mg alloys [4]. The results obtained by previous investigators [2] that each 0.1% Sc addition causes an average increase in UTS of 50 N/mm2 upto 0.4% is principally in agreement with the results shown in Table 2. A significant increase in 0.2%  y from 172 to 242 and UTS from 265 to 322 MPa is shown by increasing Sc content from 0.15 to 0.29%, however, the effect is

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not as significant on increasing the Sc to 0.62%. No beneficial effect on the increase of UTS and UTS is observed on addition of 0.9% Sc. Zirconium plays the role of a stabilizer and a strengthener. The role of zirconium is clearly observed by an increase in the strength of alloy 1 (without Scandium and Zirconium) on adding 0.14 Zirconium which almost doubles y and increases UTS. Addition of 0.14 Zr strengthens the influence of Scandium in concentrations from 0 to 3%. The particles of Al3Sc-XZrx formed during crystallization of molten metal are primarily responsible for enhancement of recrystallziation temperature and strengthening effect [4]. Zirconium dissolves in Al3Sc phase without changing the lattice cast structure. The modifying action of Sc reduces from 0.5 to 0.2% on addition of 0.1% Zr.. Sc does not form compound with Mg, Zn, or Li Mg does not enter the precipitate structure of Al3Sc. The strengthening effect of Al3Sc precipitate is in addition to the solution strengthening by Mg [4]. 350

Strength (MPa)

300 250 200

Yield Strength Ultimate Tensile strength

150 100 50 0 Al-M g0Zr-0Sc

Al-M g0.14Zr0Sc

Al-M g0.14Zr0.15Sc

Al-M g0.14Zr0.3Sc

Al-M g0.14Zr0.6Sc

Al-M g0.14Zr0.9Sc

Com position of the alloy

Fig. 6. Effect of scandium and zirconium addition on the tensile and yield strength of Al-Mg-Zr-Sc alloys.

Table 2. Mechanical properties of Al-Mg-Zr-Sc alloys.

Alloy Desig nation & Name 1 Al-Mg-Zr0.0-Sc0.0 2 Al-Mg-Zr0.14-Sc0.0 3 Al-Mg-Zr0.14-Sc0.15 4 Al-Mg-Zr0.14-Sc0.30 5 Al-Mg-Zr0.14-Sc0.60 6 Al-Mg-Zr0.14-Sc0.90

Young’s Modulus (MPa) 50220

0.2% Yield Strength (MPa) 58

56520

UTS (MPa)

% Elongation

195

14.2

110

210

10.7

58220

172

265

10.5

56460

242

322

9.1

76870

240

325

9.1

56450

220

320

10.4

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5.0 CORROSION BEHAVIOUR The results of weight loss studies of the alloys in 3.5 wt% NaCl solution are described in Table 3 and 4 and Figure 7 and 7A. Alloys 3, 4 and 5 containing 0.15, 0.3 and 0.6 Sc show a decreased loss in weight with increased exposure period. Increased Scandium content up to 0.9% does not cause a significant increase in the rate of corrosion. All alloys show a decreased tendency to corrode with time due to their strong tendency for film formation. Alloys containing scandium addition show low rates of corrosion and no appreciable increase in the corrosion rate is caused by adding 0.16, 0..29, 0.62 and 0.91% scandium as shown by Table 3. As shown by Table 3 addition of Zirconium (0.14%) to Al-Mg alloy results in a slight increase of corrosion rate after 1600 hour (0.2325 vs 0.342) mpy and addition of 0.9%Sc slightly lower the rate of corrosion rate (0.291 vs 0.268 mpy). Age hardening increase the rate of corrosion of all alloys (Figure 7-A and Table 3). Table 4 to shows the result of electrochemical polarization studies. A typical polarization plot is shown in Figure 8. These results are in confirmation with the results obtained by weight loss technique. The lower corrosion rates obtained by weight loss techniques may be ascribed to the sufficient time which is available for the formation and growth of protective film of boehmite which has been reported to be formed on the alloy surface [19]. Aging increases the rate of corrosion as shown by Table 4, however, the effect is not very pronounced because of the small initial size of the Al3Sc precipitate ( 15 nm).

Table 3. Variation of corrosion rate of Al-Mg-Zr-Sc Alloys with Time in 3.5% NaCl solution. Alloy 1

Alloy 2

Al-Mg-Zr0.0-Sc0.0

Al-Mg-Zr0.14-Sc0.0

Corrosion Rate

Alloy 3

Alloy 4

Al-Mg-Zr0.14-Sc0.15

Corrosion Rate

Alloy 5

Al-Mg-Zr0.14-Sc0.30

Corrosion Rate

Alloy 6

Al-Mg-Zr0.14-Sc0.60

Corrosion Rate

Al-Mg-Zr0.14-Sc0.90

Corrosion Rate

Corrosion Rate

mpy

mm/yr

mdd

mpy

mm/yr

mdd

mpy

mm/yr

mdd

mpy

mm/yr

mdd

mpy

mm/yr

mdd

mpy

mm/yr

mdd

200

2.1945

0.056

4.04

2.3995

0.06095

4.41508

1.597

0.0406

2.94

1.663

0.0422

3.06

3.998

0.1015

0.1015

1.5970

0.0406

2.94

400

1.5305

0.039

2.82

1.9435

0.04936

3.57604

0.815

0.0207

1.50

1.230

0.0312

2.26

2.130

0.0541

0.0541

0.9405

0.0239

1.73

600

1.0305

0.026

1.90

0.9696

0.02463

1.78406

0.699

0.0177

1.29

0.588

0.0149

1.08

0.876

0.0223

0.0223

1.0300

0.0262

1.90

800

0.5920

0.015

1.09

0.5975

0.01518

1.0994

0.549

0.0139

1.01

0.474

0.0120

0.87

0.790

0.0201

0.0201

0.8930

0.0227

1.64

1000

0.8655

0.022

1.59

1.1085

0.02816

2.03964

0.419

0.0106

0.77

0.359

0.0091

0.66

0.586

0.0149

0.0149

0.6900

0.0175

1.27

1200

0.2755

0.007

0.51

0.5225

0.01327

0.9614

0.333

0.0085

0.61

0.322

0.0082

0.59

0.577

0.0146

0.0146

0.8385

0.0213

1.54

1400

0.3825

0.010

0.70

0.423

0.01074

0.77832

0.306

0.0078

0.56

0.314

0.0080

0.58

0.532

0.0135

0.0135

0.7385

0.0188

1.36

1600

0.2325

0.006

0.43

0.342

0.00869

0.62928

0.237

0.0060

0.44

0.245

0.0062

0.45

0.299

0.0076

0.0076

0.2635

0.0067

0.48

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Table 4. Summary of Electrochemical Polarization Tests of Al-Mg-Zr-Sc alloys in 3.5% NaCl solution.

POLARIZATION RESISTANCE

TAFEL ANALYSIS

Corrosion Rate

Corrosion Rate

E(I=0) mV

P.Res. 2 K /cm

ICorr 2 A/cm

mpy

mdd

E(I=0) mV

ATC mV/decade

Al-Mg-Zr0.0-Sc0.0

-903.0

7.46

8.01

3.44

6.33

-784.20

Al-Mg-Zr0.14-Sc0.0

-764.0

18.10

2.77

1.19

2.19

Al-Mg-Zr0.14-Sc0.15

-916.7

8.74

4.79

2.06

Al-Mg-Zr0,14-Sc0.3

-835.0

7.20

7.82

Al-Mg-Zr0.14-Sc0.6

-828.0

6.43

Al-Mg-Zr0.14-Sc0.9

-865.2

5.61

Material

CTC mV/decade

ICorr 2 A/cm

mpy

mdd

177.40

611.80

6.20

2.66

4.89

-712.80

157.10

439.20

2.16

0.93

1.71

3.79

-816.90

130.50

369.40

2.71

1.16

2.14

3.36

6.18

-807.00

184.30

437.70

6.40

2.75

5.05

8.72

3.74

6.88

-787.20

176.20

484.80

8.24

3.54

6.51

9.36

4.01

7.38

-857.10

211.20

282.50

5.61

2.40

4.42

Age-Hardened (4 Weeks) Al-Mg-Zr0.0-Sc0.0

-847.5

9.32

6.40

2.75

5.05

-737.80

173.80

653.10

6.71

2.88

5.30

Al-Mg-Zr0.14-Sc0.0

-861.2

4.48

13.20

5.67

10.44

-759.80

179.90

561.20

11.18

4.80

8.83

Al-Mg-Zr0.14-Sc0.9

-894.2

6.38

6.88

2.95

5.43

-763.20

120.00

641.80

8.55

3.67

6.75

4.50 4.00

Corrosion rate (mpy)

3.50 3.00

Al-Mg-Zr0.0-Sc0.0 Al-Mg-Zr0.14-Sc0.0

2.50

Al-Mg-Zr0.14-Sc0.15 Al-Mg-Zr0.14-Sc0.30

2.00

Al-Mg-Zr0.14-Sc0.60 Al-Mg-Zr0.14-Sc0.90

1.50 1.00 0.50 0.00 0

200

400

600

800

1000

1200

1400

1600

1800

Tim e (Hours)

Fig. 7. Effect of scandium addition on the corrosion rate of Al-Mg –Zr-Sc alloys.

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1.60 1.40 1.20 1.00 Corrosion rate 0.80 (mpy) 0.60 0.40 0.20 0.00

As received Age hardened (2weeks) 1

2

3

4

5

6

7

8

Time (1 period = 200 Hrs.)

Fig. 7-A. Comparison of corrosion rate of Al-Mg-Zr 0.14-Sc 0.9 with time in 3.5% NaCl solution.

Fig. 8. Potentiodynamic polarization curves of Al-Mg-Sc alloys in 3.5% NaCl. The surface morphology shows mainly crystallographic pitting on the alloy 2 containing Al-Mg-0.14 Zr and no scandium, Figure 9. The pits are covered by the oxide layer of boehemite which was identified in an earlier work [15]. Figure (9) shows crystallographic pitting on the surface of alloy (Al-Mg-Zr0.16 Sc). No evidence of hemispherical pitting was observed.

Fig. 9. Crystallographic pitting on the surface of alloy Al-Mg-0.14 Zr exposure to 3.5% NaCl. (1000 x)

Alloy 6 containing Al-Mg-Zr-Sc0.9 shows mud cracking of the boehmite layer leading to formation of irregular pits (Fig. 10). Alloy 6 containing Al-Mg-Zr-Sc0.9 shows the formation of protective boehemite film in elliptical shapes around the white rectangular precipitate containing mostly scandium element after exposure to 3.5% NaCl for 1600 hour (Fig. 11). Numerous small circular pits are observed on the elliptical shaped protective oxide growth. Mud cracking is also observed n on the surface. The growth of the oxide around the rectangular precipitate is shown more clearly in Figure (12). It appears to be related to the growth of the oxide layer with an extended period of exposure. The age-

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hardened samples also shows crystallographic pitting. Crystallographic pitting is generally associated with a low dissolution rates. It is also revealed by this study and studies on alloy 6013, 6092 and their composites [15]. Mud cracking is a common phenomenon in these alloys and related to the breakdown. of the film at a certain thickness. The geometry and morphology of mud cracking in the above alloys is similar [20].

Fig. 10. Crystallographic pitting on the surface of alloy 3 (Al-Mg-Zr-0.15 Sc) exposed to 3.5% NaCl. (1000x).

Fig. 11. Mud cracking of the boehmite protective layer on the surface of Al-Mg-Zr-0.9 Sc exposed to 3.5% NaCl. The formation of pits is also observed (200 x). It was shown in earlier studies [15] that a maximum pit depth of 102 m was shown by Al-2.5Mg alloy and a minimum of 30 m by Al-Mg-Zr 0.3 Sc (30 m). The maximum depth measured in alloy to 5 (Al-Mg-Zr-Sc 0.6) (Sc) and alloy (3) (Al-Mg-Zr-Sc 0.9) were 120 m and 135 m respectively and the average pit depth ranged between 60-80 m. The maximum pit depth of Al-Mg-Zr 0.3 Sc from previous studies was reported to be 30 m [15]. From the above investigation it is established that

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Scandium addition up to 0.6% does not cause any appreciable increase in the rate of corrosion of AlMg-Zr-Sc alloys and pitting is not of significance as shown by surface morphology of the alloys investigated. Because of the small size of the precipitates, it has an advantage over alloys like 2024, 6061 and 6013 which contain large size precipitates of CuAl2 as Cu-Mg-Al2, since large precipitate provide active sites for intensive pitting [21]. From the above studies it is established that Scandium up to 0.6% can be used as a strengthener without any increased risk of corrosion and the excellent combination of mechanical properties of Al-Mg-Zr-Sc alloy is further supported by its good resistance to corrosion.

Fig.

12.

Growth of elliptical oxide boehmite around white precipitate in Al-Mg-Zr-0.9 Sc alloy exposed to 3.5% NaCl (2000 x).

7.0 CONCLUSION On the basis of the observation presented above, the following conclusion can be drawn: 1. The addition of 0.3% Sc to Al-Mg-Zr 1.4 alloy brings about a maximum increase in the strength levels, improvement levels are not significantly improved with 0.6 and 0.9% Scandium addition. 2. Small amount of zirconium 0.14% allows higher strength of mechanical strength to be achieved by a smaller Sc content (0.3% Sc). 3. Microstructural studies show the presence of Al3Sc precipitate of very small size ( 25 m). These precipitates pin down the grain boundaries as shown by TEM studies. This precipitate is primarily responsible for the strengthening effect. 4. The scandium added Al-Mg alloys (0.15-0.9% Sc) show low corrosion rates in 3.5 wt% NaCl. 5. Age hardening for 15 days at 290oC does not cause any significant increase in the rate of corrosion. 6. The Al-Mg-Zr-Sc alloys show only crystallographic pits with small pitting depths. They exhibit a strong tendency to form a protective boehmite films.

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By virtue of an outstanding combination of strength, outstanding mechanical properties and a good resistance to corrosion, these alloys could be exploited in marine and salt water environment with a minimum risk of corrosion. They are being exploited as materials for super yachts and speed boats. ACKNOWLEDGEMENTS The authors appreciate the encouragement and help provided by KFUPM in pursuing this work. The authors thank Mr. M. Saleh for his dedicated assistance in the experimental work.

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Ralph R. Sawtell and Craig L. Jensen, Mechanical Properties and Microstructures of Al-Mg-Sc Alloys, Metallurgical Transaction, Vol. 21A, (1990), p. 421.

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V.I. Elagin, Alloying of Wrought Aluminium Alloys with Transition Metals, Metallurgiya, 23, (1975), p.11, Moscw.

6.

E.W. Lee, T.R. McNelley and A.F. Stengel, Constitution and Age Hardening of Al-Sc Alloy, Metall Trans A, Vol. 17A, (1986), p. 1043-1050.

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T.R. McNelley, E.W. Lee and M.E. Mills, Metall Trans. a. Vol. 7A, (1986), pp. 35.

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Lawrence S Kramer and William T. Tack, Scandium in Aluminum Alloys, Alumtech Cong, 19-23rd May, Atlanta, 1997.

10. Elagin, V.I., Zakharov, V.V., Rostova, T.D. and Filatov, Yu. A., Tekhnol, Leg K. Splavov, No. 2, (1991), p. 21. 11. Sinyavskii, V.S., Valkov, V.D., and Kalinin, B.D., Korroziya Zashchita Alyuminievkh Splavov (Corrosion and Proteciton of Aluminum Alloys), Moscow: Metallurgiya, (1986), p. 79. 12. Sinyavskii, V.S., Val’Kov, V.D., and Titkova, E.V. Protection of Metals, Vol. 34, No. 6, (1988), p. 613. 13. Filatov, Yu. A., Elagin, V.I., and Zakharov, V.V., Tekhnol, Leg K Splavov, (1977), p. 8. 14. Vyazovi Kina N.V. , Protection of Metals, Vol. 35, No. 5, (1999), p. 448. 15. Zaki Ahmad, Anwarul-Hamid and Abdul Aleem, B.J., Corrosion Science 43, (2001), pp. 1227.

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