Strength and Hardness of Directionally- Rolled AA1230 ...jeteas.scholarlinkresearch.com/articles/Strength and Hardness of... · Strength and Hardness of Directionally- Rolled AA1230

Journal of Emerging Trends in Engineering and Applied Sciences (JETEAS) 2 (3): 440-444 (ISSN: 2141-7016)

440

Strength and Hardness of Directionally- Rolled AA1230 Aluminum Alloy

Samson Oluropo Adeosun; Wasiu Ajibola Ayoola;

Muideen Bodude; and Samuel Olujide Sanni

Department of Metallurgical and Materials Engineering,

University of Lagos, Akoka -Yaba, Lagos, Nigeria

Corresponding Author: Wasiu Ajibola Ayoola

___________________________________________________________________________ Abstract

There are processes that have been utilized to improve the tensile strength and hardness of aluminum alloys,

some of which include elemental and particle additions, since work hardening cannot be used to improve

strength and hardness of 1xxx wrought aluminum alloys. This work examines the possibility of introducing

secondary processing of transverse rolling after the initial primary rolling to strengthen and hardened wrought

aluminum alloy. The effects of transverse and longitudinal rolling on the tensile strength and hardness of

AA1230 aluminum alloy worked at ambient temperature (32 oC) have been studied. Samples were rolled in

longitudinal and transverse directions from thickness of 1.55 mm to 0.45 mm in 3-7 passes in two-high

irreversible mill. The samples rolled in transverse direction have hardness and tensile strength which are

superior to samples rolled in the longitudinal direction. The resultant crystals in transverse directions were

elongated in the rolling direction and agglomerate into larger crystals in this direction.

__________________________________________________________________________________________

Keywords: transverse direction, longitudinal direction, microstructures, hardness, tensile strength

________________________________________________________________________________________

*OME*CLATURE

1A 78 % deformation parallel to the rolling direction

1B 78 % deformation perpendicular to the rolling direction










6B 94% deformation perpendicular to the rolling direction

I*TRODUCTIO* Recent technological advancement in aerospace,

automotive, marine, construction and leisure

industries has made the demand for materials having

high strength to weight ratio, high specific modulus,

good corrosion resistance and good thermal

conductivity to be on the increase (Myer, 2002).

Aluminum and its alloys offer such combination of

tremendous properties. Aluminum 1230 alloy can be

manufactured into semi-finished or finished products

using techniques such as forging, rolling, welding,

casting e.t.c (Myer, 2002 and Polmear, 1995).The

mechanical properties of this alloy are better when

mechanically worked at temperatures below or above

it recrystallization temperature (Suraj, 2001; Zainul

2009; and Perovic, 1999). During cold working,

dislocation motions within metal matrix are restricted

resulting in strength increment as its shape is

changed. Structural components made from such

strengthened alloys are vital to the building,

aerospace and transportation industries, as well as for

the production of utensils for domestic use. Several

studies have been carried out on wrought aluminum

alloys (Ibrahim, 2007; Ming-xing et al, 2008; Sh

Ranjbar et al, 2010 and Lee et al, 2011) to understand

the effects of mechanical workings on its mechanical

properties. The effects of post rolling after the twist

extrusion process on commercially pure aluminum

were considered by Sh Ranjbar et al (2010). The

results show that both the hardness profile and bulk

strength were enhanced with post rolling. In addition,

the microstructural evolutions showed that post

rolling not only reduces the grain size but also

reduces the heterogeneity of microstructure across the

longitudinal section. Aluminum alloy sheets

fabricated by direct chill (DC) and continuous casting

(CC) routes were investigated by Lee et al, (2011).

The aluminum sheet produced through heavy cold-

rolling and recovery anneal exhibits highly

anisotropic tensile properties, and poor ductility at

45o from the rolling direction. This ductility was

attributed to the evolvement of intense shear bands

which is triggered by the yielding phenomenon in DC

specimens and less severe in CC. In both DC and CC

sheets, increasing strain rate enhance the strength and

also improved the ductility.

In this paper the effect of transverse and longitudinal

rolling on tensile strength and hardness of AA1230

aluminum alloy at ambient temperature are presented,

as a compliment to the results of post rolling effects

discussed by Sh Ranjbar et al (2010).

Journal of Emerging Trends in Engineering and Applied Sciences (JETEAS) 2 (3): 440-444

© Scholarlink Research Institute Journals, 2011 (ISSN: 2141-7016)

jeteas.scholarlinkresearch.org


441

EXPERIME*TAL PROCEDURE

Cold rolled aluminum 1230 sheet with thickness 7.20

mm used in this study was provided by Aluminum

Rolling Mills, Ota, Nigeria, and its nominal chemical

composition is given in Table 1.

Table 1: Chemical Composition of AA1230 Aluminum Alloy Sheet (Aluminum Rolling Mills, Ota, Nigeria,

2010)

Elements Fe Si Mn Zn Ti Pb Sn Mg Cu Al

Weight (%) 0.441 0.19 0.008 0.02 0.012 0.002 0.006 0.001 0.017 99.303

The sheet obtained from the rolling mills was blanked

into 20 x 20 x 7.20 mm samples and rolled at ambient

temperature (32 oC) in a two-high irreversible mill.

The thickness and percent reduction of the samples

produced are 1.55 mm (78 %), 1.08 mm (85 %), 0.85

mm (88 %), 0.60 mm (92 %), 0.47 mm (93 %) and

0.45 mm (94%) in accordance with ASTM E8-8ST

standard. These were produced in 3, 4, 5, 6, 7 and 7

passes, respectively, in both the longitudinal and

transverse directions (see nomenclature).

Hardness test was conducted by polishing each test

sample with emery papers down to 1000 mesh prior

to using the Webster hardness tester Model B. Ten

(10) measurements were taken for each sample and

the mean hardness determined. The mean hardness

values of the samples were converted to Rockwell

using Rockwell E scale. The tensile strengths of the

test samples were determined using a Monsanto

Tensometer in accordance with ASTM 1414

specifications. Samples were prepared for

metallographic examinations using Modern Wet-

grinding Machine. Four strips of 300 mm x 50 mm

emery paper (water proof base) were clamped, side

by side, on a sloping glass. The samples were then

pressed against the rotating paper with a stream of

water acting as coolant and particles remover. Coarse

grinding was done with emery papers of meshes 60,

240,320 followed by fine grinding with 600 and 800

meshes. The ground and polished samples were

etched in sodium hydroxide solution for 20 seconds.

The etched samples morphologies were examined

using a Digital Metallurgical Microscope at a

magnification of 100X.

The rolling process, tensile and hardness tests were

carried out using facilities at Aluminum Rolling Mills

Ota, Ogun State Nigeria while the microstructural

analysis was done at Metallurgical and Materials

Engineering laboratory of the University of Lagos,

Nigeria.

RESULTS A*D DISCUSSIO* Table 2 show the results of hardness and tensile tests

carried out on the samples. Increase in degrees of

deformation increases the hardness values from 52-

54Hv between 78-92 percent reduction and decreases

to 50 Hv between 92-94 percents reduction. During

cold rolling of wrought aluminum 1xxx alloy,

dislocation density increases as the degree of

deformation increases. Immobile dislocations are

created by the complicated network of interlocking

dislocations and this is responsible for its increase

work hardening rate resulting in hardness and

strength increment but with lost in ductility (Davis

and Oelmann, 1983) (see Figures 1-6). As

deformation processing increases from 93 to 94

percents more dislocations become mobile due to

unmerge of interlocking dislocations. This

eventually resulted in reduction in hardness and UTS

values of the alloy.

Figure 1 shows the stress-strain behaviour of the

samples at 78 % reduction in both the longitudinal

and transverse directions. The tensile strengths

response in these directions are linear and the same at

ε < 0.02. However, beyond this level, samples

strength in longitudinal direction surpasses that of the

transverse direction at the same strain up to 0.055

strain with ultimate tensile strength of 195.16 MPa.

However, sample deformed in the transverse

direction has superior UTS of 204.3 MPa. It should

be noted that the elongation responses are

independent of direction of rolling but the stress at

fracture depends on working direction.

In Figure 2, at 85 % reduction the strengths of the

alloy are higher in transverse than longitudinal

direction. At tensile strain of 0.05, UTS are almost


442

equal (206.79 MPa-transverse and 206.22 MPa-

longitudinal) in both directions. The strains at

fracture are the same (0.068) and stress at fracture

very similar with negligible difference.

Samples deformed at 88 % show similar trend to that

at 85 % reduction (see Figure 3). The strains in the

deformation directions are similar at ε < 0.015. At ɛ >

0.02, the sample deformed in transverse direction

exhibited higher stresses.

Figure 4 show samples deformed at 92 % reduction

in both directions. Samples have slightly superior

strength in transverse direction than its longitudinal

direction at ε > 0.014.

In Figure 5, the deformed alloy at 93 % thickness

reduction possess similar strengths in both transverse

and longitudinal directions at 0 < ɛ ≤ 0.01. The

longitudinal direction deformed sample has UTS of

225 MPa (ɛ = 0.02), while UTS in the transverse

direction is slightly lower (220 MPa, ɛ = 0.03).

However, the elongation of the sample in the

transverse direction is superior (0.036) to that in the

longitudinal direction.

But, at 93 % thickness reduction (see Figure 5)

absence of structural homogeneity persists.

At 94 % thickness reduction, the sample morphology

indicates homogeneity in the texture of phases

precipitated. For ε ≤ 0.011, longitudinal and

transverse strengths responses are identical, but at

0.011 < ε < 0.017 stresses are higher in the

longitudinal direction than the transverse. However,

in the transverse direction UTS of 222.22 MPa is

achieved compared to 212.96 MPa in the longitudinal


443

direction while the difference in samples’ elongations

with direction of deformation is negligible (Figure 6).

In this investigation, the strain at fracture decreases

as degree of deformation increases and it is

independent of test direction. The thickness reduction

at 78, 85, 88, 92, 93 and 94 percent produced

elongations of 7, 6.9, 5.3, 3.6 and 2.5 respectively in

the longitudinal direction and 7, 6.9, 4.8, 5.1, 3.5 and

2.4 respectively in the transverse direction. Thus

ductility of alloy decreases with degree of

deformation but does not differ appreciably with test

direction.

Table 2 Hardness and Ultimate Tensile Strength of

aluminum 1230 alloy with percent deformation (Authors

Computation, 2011)

Deformation (%)

Hardness

(HV)

Ultimate Tensile Strength (MPa)

Longitudinal A Transverse B

78

85

88

92

93

94

52

52

54

54

50

50

195.16

206.79

207.84

222.22

225.01

212.96

204.30

211.41

222.54

230.55

220.00

222.22

Plate 1a shows the microstructure of as-received

rolled sample. The matrix contains AlFeSi and α-

aluminum phases in approximately equal volume

fractions with other intermetallics predominately

FeAl3. The crystals of FeAl3 are finely dispersed

within the matrix phase while some of its crystals are

found at the grain boundaries. When the alloy sample

was deformed longitudinally with 78 % thickness

reduction, the α-aluminum and AlFeSi crystals

elongated along the deformation direction (see Plate

1b). The volume fraction of AlFeSi phase decline as

more crystals of FeAl3 are precipitated. But in the

transverse direction crystals of AlFeSi phase are

evenly distributed within the matrix, while crystals of

FeAl3 lie side by side with α-Al crystals (see Plate

2a).

Increase in thickness reduction from 78 to 85 %

across the rolling direction resulted in the dissolution

of FeAl3 crystals into the α-aluminum solvent (see

Plate 1c). The α-aluminum crystals are seen broken

up forming channel-like feature along the transverse

rolling direction. AlFeSi phase is still visible and its

crystals are finely distributed in the matrix.

Samples deformed at 85 % thickness reduction show

that deformation has significant effect on intensity,

distribution, orientation and volume fractions of the

phases present. In the rolling direction the intensity of

the FeAl3 phase decreased (see Plate 2b) when

compared with that deformed at 78 % thickness

reduction.

In transverse direction at 88 % thickness reduction

the alloy matrix contain needle-like crystals of the α-

Al phase with very fine crystals of FeAl3 (see Plate

1d) than those found in Plate 1c. Increase in degree of

deformation caused reduction in volume of AlFeSi

crystals that are precipitated. In Plate 2c, however,

deformation in longitudinal direction caused coarse

a b c

d e f

g Plate 1 Microstructure of rolling sample in the

longitudinal direction with thickness reduction.

(a) as-cast (b) 78 (c) 85 (d) 88 (e) 92 (f) 93 (g) 94

a b c

d e f Plate 2 Microstructure of rolling sample in the

transverse direction with thickness reduction

(a) 78 (b) 85 (c) 88 (d) 92 (e) 93 (f) 94


444

formation of α-aluminum crystals and dissolution

into the matrix of some crystals of FeAl3 and AlFeSi

phases. The deformation also caused stretching of

AlFeSi crystals.

As deformation progresses to 92 % thickness

reduction, there is an increase in the amount of FeAl3

crystals in the matrix (Plate 1e). These crystals are

uniformly distributed with higher volume fraction to

sample tested in longitudinal direction (see Plate 2d).

It was observed in Plate 2d that the 92 % thickness

reduction in transverse direction causes fine

segregation of AlFeSi and elongation of crystals of

α-aluminum.

Plate 1f shows sample deformed in longitudinal

direction at 93 % thickness reduction. Crystals of

FeAl3 are absorbed by the α-Al matrix with

consequent increase in the volume fraction of α-

aluminum phase compared to that in Plate 2e. The

crystals of α-aluminum phase are seen stretched in

the deformation directions.

Further increase in degree of deformation in

longitudinal direction (94 %) enhanced uniform

distribution of all the three major phases precipitated

(see Plate 1g). The α-aluminum and AlFeSi phases

are fine and devoid of segregation. The effect of

rolling direction on the alignment and orientation of

the phases are negligible. However for sample rolled

at 94 % reduction in the longitudinal direction,

needle-like shaped crystals of α-aluminum are formed

within the matrix (see Plate 2f) while the volume

fraction of FeAl3 phase increase with decrease in

volume fraction of AlFeSi phase.

CO*CLUSIO*

This study has shown that before yielding at small

strains, the mechanical properties of 1230 aluminum

alloy are independent of deformation directions and

amount of reductions taken.

For alloy 1230, maximum hardness of 54 Hv can be

obtained at 92 % reduction and with superior strength

of 230 MPa in the transverse direction. Transverse

rolling of the alloy would be preferred as the

mechanical properties are unlikely to be

compromised.

Strain at fracture decreases as degree of deformation

increases and it is independent of test direction. The

ductility of this alloy decreases with degree of

deformation and does not differ appreciably with

direction of test.

REFERE*CES

Davis, D. J., and Oelmann, A., 1983, The Structure,

Properties and Heat Treatment of Metals. Piman

Books Limited.

Ibrahim, O., 2007 “A Study on the Re-solution Heat

Treatment of AA2618 Aluminum Alloy” Materials

Charaterisation, 58(3) 3, 312-317.

Lee, N. H., Chen, J.H., Kao, P.W., Tseng T.Y., and

Su, J.R., 2011, “Anisotropic Tensile Properties of

Recovery annealed Aluminum Alloy sheet” Materials

and Engineering A 528(4-5), 1979-1986.

Ming-xing G., Ming-pu W., Shen-fei C., Ruo-shan

L., and Shu-mei L., 2008 “ Effects of Cold Rolling of

Properties and Microstructures of Dispersion

Strengthened Copper Alloys” Trannsactions of

Nonferrous Metal Society of China 18, 333-339.

Myer, K., 2002, Handbook of Materials Selection.

John Wily and Sons.

Perovic, A., Perovic, D.D., Weatherly, G.C., and

Lioyd, D.J, 1999 “Precipitation in Aluminum Alloys

AA6111 and AA6016” Scipta Materialia, 41(7), 703-

708.

Polmear, I.J., 1995, Light Alloys, Metallurgy of the

Light Metals, London, Arnold.

Sh Raanjbar B., Akbari S. A. A., and Shab A.R.,

2010 “Sequence effects of Twist Extrusion and

Rolling on Microstructure and Mechanical Properties

of Aluminum Alloy 8112” Journal of Physics:

Conference Series 240, 1-5.

Suraj, R., 2001 “Metal-Matrix Composites for Space

Application” JOM, 53(4), 14-17.

Zainul, H., 2009 “Precipitation Strengthening and

Age-Hardening in 2017 Aluminum Alloy for

Aerospace Application” European Journal of

Scientific Research, 26(4), 558-564.

Documents

Strength and Hardness of Directionally- Rolled AA1230 ...jeteas.scholarlinkresearch.com/articles/Strength and Hardness of... · Strength and Hardness of Directionally- Rolled AA1230