SURFACE MODIFICATION OF AA 7075-T651 PLATE USING … › en › research › journal › issues › v23 › pdf › paper_1.pdfFigure 1: major steps of friction stir processing [2]

Emirates Journal for Engineering Research, 22 (3), 1-11 (2017)

(Regular Paper)

1

SURFACE MODIFICATION OF AA 7075-T651 PLATE USING

FRICTION STIR PROCESSING WITH SIC PARTICLES

Ayad M.Takhakh Mechanical Engineering Dept.

Al- Narhain University

[email protected]

Harith Hammody Abdulla Mechanical Engineering Dept.

University of Baghdad

[email protected]

(Received 28th

April and Accepted 9th

September 2017)

بإسخخذام SiCوهقواة بواسطت سلينوى الناربايذ T651-7075في ُذا البحث, حن حصٌيع سطح هزمب هنوى هي هعذى اساس هي سبينت االلوٌيوم

. وجذ هي عيٌاث AA7075-T651. حوج دراست الصالدة الذقيقت للسطح الوعالج وهقارًخَ بصالدة السبينت بالخلظ واالحخناك طزيقت الوعالجت

فخحخيي بواسطت الطزيقت الوباشزة هي خاله SiCالوعالجت بالخلظ واالحخناك اى صالدة السطح الوعالج اعلى هي صالدة السبينت االصليت. حن اضافت

احخوث العذة هيل. عذة هجوفت محاويت لحفظ هسحوق السيزااسخخذهج عذة بخصوين جذيذ في ُذٍ الذراست. حن حصٌيع في وجَ مخف العذة. ًافذحيي

لضغظ الوسحوق هي خاله اليت هيناًينيت اسخخذهج موا ثقبيي في وجَ العذة اليصاه هسحوق السيزاهيل هي حجويف العذة الى هٌطقت الوعالجتعلى

باسخخذام سلينوى دقيقت\هلن 81دقيقت و سزعت اًخقاليت \دورة 1681بوحذاث فينزس عٌذ سزعت دوراًيت 111الفخحخيي. اعلى صالدة ماًج هقاست

هاينزوهيخز. 5.7ماربايذ بحجن

In the present work, composite surface based on AA 7075-T651 matrix reinforced with micro-sized particles of silicon

carbide (SiC) has been fabricated by Friction stir processing (FSP). The micorhardness of the processed surface has been

investigated and compared with that of base alloy AA 7075-T651. It is found that the friction stir processed sample

possesses higher hardness than that of AA 7075-T651. The Addition of SiC was done using the direct method through holes

in shoulder face. A new tool design has been manufactured for this study. A hollow tool used as a reservoir for ceramic

powder. Two holes in shoulder face used to insert the ceramic powder from the cavity to processing zone. A mechanical

system is been used to pressed ceramic powder through holes. The maximum hardness is 211 HV was observed at 1460

rpm, rotating speed 60 mm/min, traveling speed with particle size 3.5 µm for SiC.

1. Introduction

Friction Stir Processing is a solid-state mechanical

process which developed with the concepts of

friction Stir Welding. The local composition and

properties of a material can be modified without

changing the bulk properties of the base metal.

Thus, FSP is considered one of the surface

engineering techniques in which the surface

properties can be modified according to the

engineering requirements. This process consists of

a rotating tool with a pin and shoulder. It inserts

into the material surface and then moves and

simultaneously rotates with speed under the

suitable load. The primary functions of non-

consumable rotating tool are (1) heating the

specimen in the localized zone (2) moving and

transporting the materials within the processing

zone and (3) to facilitate mixing up of base

material and externally added material to produce a

composite material within the processed zone. As a

result, the processed zone becomes a metal matrix

composite with improved wear resistance and the

hardness. [1]

Friction Stir Processing (FSP) process has been

introduced as a surface modification technique to

produce composite surfaces. SiC particles, Al3Ti,

nickel particles and Al2O3 were separately

embedded in Al matrix by FSP to fabricate

composite materials. Figure 1 shows the step by

step procedure of Friction Stir Processing, step (a)

including; machining a groove to insert ceramic

powder, step (b) closing the upper surface of a

groove by a flat tool and step (c) heating and

stirring the ceramic particles with a base metal

using FSP tool. [2] Ramesh and Murugan, [3] they experiment AA

7075-T651 plates. They use plate thickness

6.35mm and they made a groove of 2.5 mm depth,

0.5 mm width and 100 mm length along the plate.

Boron carbide powder has size 5 micrometers used

to fill the grooves. They used one pass and multi

passes up to 3. They found maximum hardness 64

BHN was at rotation speed 575 rpm and travel

speed 60 mm/min with 2 passes. They found that

the average hardness of the processed surface was

62% higher than that of the base metal AA 7075 –

T651.

Sudhakar et al,[4] studied a processing of Al7075-O alloy with boron carbide has size 30 µm.The

maximum hardness and tensile strength have gotten

at 960 rpm rotating speed and 60 mm/min traveling

speed.

Yongxian, et al, [5]they fabricated AZ31 Mg

matrix composite using carbon nanotubes of SiC.

They used the direct Friction Stir Processing

mailto:[email protected]:[email protected]

Ayad M.Takhakh and Harith Hammody Abdulla

2 Emirates Journal for Engineering Research, Vol. 22, No.3, 2017

(DFSP) to produce composite surface. In DFSP

method, no need for grooves to insert ceramic

powder. DFSP method includes using a hollow tool

and without pin to produce the composite surface.

They used DFSP for the AZ31 plate. They found

the thickness of the composite layer is 150 µm. The

microhardness of surface increased from 57.77 HV

to 115.51 HV.

In the present work, a new tool design is proposed.

FSP tool with a pin is used to add SiC particles

directly to stirring zone through holes in the

shoulder face. The advantage of pin in this design

is improving the mixing process of ceramic

particles with a base metal and increasing the

generated heat by friction.

Two different particle sizes are used to study the

effects of particle size on hardness of AA7075-

T651 alloy. The ceramic particles fall during the

process by applying mechanical pressure using a

helical spring.

Figure 1: major steps of friction stir processing [2]

2. Experimental Procedure

Aluminum AA7075-T651 plates of size 6.35 x 50 x

200 mm were used. The chemical composition of

AA7075-T651 is given in Table 1. The tool is made

of high chromium-alloy steel, The FSP process

parameters are identified as rotational speed (RS),

traveling speed (TS) and particle size of ceramic

(PS).

The addition of SiC particles into the matrix alloy

significantly increases the hardness and decreases

elongation of the composites in comparison with

those of the base alloy [6]. SiC with two different

particle sizes 19 and 3.5 µm. Ceramic powders 19

µm and 3.5 µm have specifications shown in Table

2. Particles sizes are selected according to previous

references [7].

Vertical milling machine was used to prepare the

FSP plates, see Figure 2. The experimental

parameters were selected as shown in Table 3. The

specimens were prepared from the FSP samples.

The Tool design is shown in Figure 3. The hollow

tool is used to fill it with SiC particles. Thickness

of metal for shoulder face is 5mm. The generated

heat equation below show thickness of shoulder is

not effective factor for shoulder thickness on

amount of generated heat.

………………. (1)

Where:

δE – slip ratio, μ – coefficient of friction between

the FSP tool and the surface of the material, PN –

pressure exerted by the tool on the material being

processed, ω – tool rotational speed, r – distance

between the tool axis and a tool surface fragment

under consideration, vx – tool travel rate and Θ –

angle between the tool axis and a fragment under

consideration [8].

A thin disc of polystyrene foam has thickness 2

mm; it placed inside the tool cavity to prevent fall

the SiC powder at the beginning of the process. In

the beginning of FSP process the heat of tool rises

gradually to reach high temperature near 80 percent

of melting temperature of the base metal (about 450

ᵒC)[9]. At 240 ᵒC temperature the polystyrene disc

will melting and evaporate [10], that allow to the

powder particles to passes through holes. After disk

evaporating, powder particles will extrude through

holes due to pressing of piston due to releasing of

compressed spring. A piston of steel is put in the

cavity after filling the tool with 2 grams of the SiC

(a) (b) (c)

SURFACE MODIFICATION OF AA 7075-T651 PLATE USING FRICTION STIR PROCESSING WITH SIC PARTICLES

Emirates Journal for Engineering Research, Vol. 22, No.3, 2017 3

powder. It has been used to push the powder.

Helical spring is used to supply a continuous force

to press the ceramic particles to extrude through the

two holes, see Figure 4. A piece of aluminum foil is

placed on the shoulder to close two holes before

start the process After starting the foil will torn by

friction between the shoulder and workpiece

surface and polystyrene will melt and evaporate

due to increase temperature of the tool when the

tool shoulder starts to touch the workpiece.

The experiments were designed based on two level-

three factors factorial technique. The developed

design matrix is shown in Table 4. Four samples

prepared as shown in Figure 5. Eight specimens

were prepared, four specimens for surface

inspection and four for thickness inspection. After

mounting and preparing the specimens, they are

inspected by Vickers hardness test. “Zwick-Roell”

tester type ZHV is used to measure hardness

according to 0.3 kgf / 3s [11]. Microhardness is measured on upper surface and thickness side of

the processed surface. The microhardness for the

base metal measured and it was 170 HV.

Table 1: Chemical Composition of A7075 Alloys

Element Mg Mn Zn Fe Si Ti Cr Cu Al

Nominal composition of Al 7075-T651 [4] Wt.% 2.1-2.9 0.30 5.1-6.1 0.50 0.40 0.20 0.18-0.28 1.2-2.0 Bal.

Measured Chemical composition of Al 7075-T651 Wt.% 2.33 0.03 5.73 0.19 0.085 0.03 0.189 1.45 Bal.

Table 2: SiC Powder Specifications

Designated grit 1200

Median grain size ds(µm) 3.5+-0.5

Purity 97+-97.8

Table 3: Selected Parameter for FSP

Rotating Speed

(rpm)

Travelling Speed

(mm/min) Particle Size (µm)

930 40 19

1460 60 3.5

Figure 2: Vertical Milling Machine Used for FSP.

Figure 3: Sketch of Tool Design and Its Dimensions



Figure 4: Section View for Tool Assembly

Table 4: Design Matrix and Estimated values

Experimental Trial Design Matrix

RS (rpm) TS(mm/min) PS (µm)

1 930 60 19 2 930 40 3.5 3 1460 60 3.5 4 1460 40 19

Figure 5: Picture of Processing Plates

3. Results and Discussion

The Microhardness is measured for surfaces of the

four specimens. The average for microhardness

results of processing zone are shown in table 5. The

hardness measurements for specimens are shown in

figure 6. Figure 7; the optical microscope image

shows the SiC particles distribution in processed

metal. In Figure 8; SEM image of the SiC particles

size 3.5 µm. Figures 9, 10 show composite surface

which fabricated using FSP. The gray particles are

SiC. As it shown in Figure 10 the distribution of

SiC particles can be observed.

Figures 11, 12, 13 and 14 show SEM images and

EDS analyses for many regions in the processed

surface. Percentages for C elements in EDS

analyses represent SiC percentages because there is

not C element in base metal. These results show the

distribution of SiC in the composite surface. Figure

13 show spreading of SiC particles in the fabricated

surface.

In Figure 15 (a) and (b) : EDS analysis for SiC Wt.

% percentages in Spectrum 21 and 23 respectively.

The percentages were 18.3 and 24.6.

It is found that the microhardness for composite

surface was higher than base metal hardness with

212 HV; figure 16 shows the microhardness at a

thickness of sample S3 which has highest average

of microhardness for the processed zone.

The heat treatable Al7075-T651 becomes softened

after processing and its hardness fall down in the

processing zone as in FSW process, see Figure 17.



After adding the SiC particles to alloy surface, the

hardness increases due to insertion the hard

particles in the alloy.

The increase in hardness was attributed to the

presence for powders have high modulus of rigidity

(400GPa) and for fine dispersion of SiC particles

and fine grain size of the Aluminum matrix [12].

Pressing the SiC powder in the stirring zone

improve the distribution and insertion in the base

metal. The effects of traveling speed, rotating speed

and SiC particles size on hardness was presented in

Figure 18. By using the mathematical equations,

graphs have been plotted between traveling speed

Vs. Vickers hardness, Rotating speed Vs. Vickers

hardness and particle size of particles Vs. Vickers

hardness. From Figure 18 it has been observed that

when the traveling speed increases hardness due to

the reduction in heat input. when traveling speed is

low the amount of heat input is high due to stirring

and friction effects which will in same area for long

time. When traveling speed increase the heat input

for same area (as mentioned before) will be for

lesser time, therefore the growth of base metal

grains will be less. According for Hall-Petch

formula the hardness will be higher for smaller

grain size. From the Figure 18 it has been observed

that when the rotating speed increases, the hardness

decreases due to irregular distribution of ceramic

particles.

Table 5: Average Hardness of specimen’s measurements

Specimens

No.

Parameters HV

RS (rpm) TS(mm/min) PS(µm)

S1 930 60 19 200 S2 930 40 3.5 199 S3 1460 60 3.5 206 S4 1460 40 19 192

Figure 6: Hardness Measurement for Processing Surface

Figure 7: SiC Particles Diffused in Aluminum Structure

SiC particles

_____

200 µm



Figure 8: SEM Micrographs for SiC Particles

Figure 9: SEM Micrographs of The Precipitate Dissolve SiC Particles in AA7075-T651

Figure 10: SEM Micrographs of Distribution for SiC Particles

SiC particles



Figure 11: SEM/EDS Image and Analysis of The Specimen No. S3 Shows Percentage of SiC is approximately 50.3 Wt. % in

Green Region.

Figure 12: EDS Analysis of The Specimen No. S3: Shows Percentage of SiC is approximately 19.7 Wt. % Pink Region.

Figure 13: EDS Element Mappings for C



Figure 14: EDS Analysis for two Spectrum 21 and 23.

Figure 15: EDS Analysis Shows Percentage of C in Spectrum 21 and 23.

Figure 16: Hardness Measurement for Thickness of Sample S3 .

(a) (b)



Figure 17: Effect of FSW on The Hardness of Welded Joint of Al 7075-T651 after different hours (h) for natural aging [13]

Figure 18: Effect of Parameters of rotating speed (RS) ,traveling speed (TS) and particle size (PS) on Hardness

4. Conclusions

From recent study, it can be concluding:

1- It has been recorded that the average microhardness value is 206 HV occurs

when the processing speed 1460 rpm and

traveling speed 60 mm/min respectively.

2- FSP using particle size 3.5 µm of SiC particles show better microhardness

results.

3- Using new tool design for DFSP is efficient in improve of surface hardness

with percentage 21%. Mechanical

pressing of ceramics powder succeed in

inserting the SiC particles to processing

zone.

References

1 - Prakrathi Sampath, Vineeth Krishna

Parangodath, Kota Rajendra Udupa, and Udaya

Bhat Kuruveri. 2015 . Fabrication of Friction Stir

Processed Al-Ni Particulate Composite and Its

Impression Creep Behaviour. Journal of

Composites Volume 2015, Article ID 428630.

2- Yongxian Huang , Tianhao Wang, Weiqiang

Guo, Long Wan, Shixiong Lv. 2014.

Microstructure and surface mechanical property of

AZ31 Mg/SiCp surface composite fabricated by

Direct Friction Stir Processing. Materials and

Design. vol 59. 274–278.

3 - R. Ramesh and N. Murugan. 2013.

Microstructure and Metallurgical Properties of

Aluminium 7075 – T651 Alloy / B4c 4 % Vol.

Surface Composite by Friction Stir Processing.

Advanced Materials Manufacturing &

Characterization Vol3 Issue 1. 301-306.

(RPM) (mm/min) (µm)



4- Sudhakar. I, Madhusudhan Reddy.G and

Srinivasa Rao.K. 2013. Efficacy of Friction Stir

Processing in Fabrication of Boron Carbide

Reinforced 7075 Aluminium Alloy. International

Conference on Multidisciplinary Research &

Practice,Vol I, pp 162-165.

5 - Yongxian Huang , Tianhao Wang, Weiqiang

Guo, Long Wan, Shixiong Lv. 2014.

Microstructure and surface mechanical property of

AZ31 Mg/SiCp surface composite fabricated by

Direct Friction Stir Processing. Materials and

Design, vol 59, p 274–278.

6 - A.R.I. Kheder ,G.S. Marahleh ,D.M.K. Al-

Jamea. 2011. Strengthening of Aluminum by SiC,

Al2O3 and MgO. Jordan Journal of Mechanical

and Industrial Engineering, v 5. 533 – 541.

7 -Zhangwei Wang, Min Song, Chao Sun, Yuehui He. 2011. Effects of particle size and distribution

on the mechanical properties of SiC reinforced Al–

Cu alloy composites. Materials Science and

Engineering A 528. 1131–113.

8 - Marek St. Węglowski, Carter Hamilton. 2013.

Investigation into friction stir processing (FSP) of

surface layers. INSTITUTE OF WELDING

BUILETYN, 5-19.

9- T. Azimzadegan, Gh. Khalaj, M. M. Kaykha,

A.R. Heidari. 2011. Ageing Behavior of Friction

Stir Welding AA7075-T6 Aluminum Alloy.

Computational Engineering in Systems

Applications- Volume II, 183-187.

10 - James E. Mark. 2007. POLYMER DATA

HANDBOOK. Oxford University Press, Inc. 832,

1999.

11 - Omar Hatamleh , Jed Lyons , Royce Forman.

2007 .Laser and shot peening effects on fatigue

crack growth in friction stir welded 7075-T7351

aluminum alloy joints. International Journal of

Fatigue 29, 421–434.

12- Mageshwari Komarasamy, Rajiv S. Mishra,

John A. Baumann, Glenn Grant, Yuri Hovanski.

2013. Processing, Microstructure and mechanical

property Correlation in Al-B4C Surface Composite

Produce via Friction Stir Processing. Friction Stir

Welding and Processing VII.

13- - Rajiv S. Mishra, Murray W. Mahoney. 2007.

Friction Stir Welding and Processing. ASM

international –the materials information society ,

97.

SURFACE MODIFICATION OF AA 7075-T651 PLATE USING … › en › research › journal › issues › v23 › pdf › paper_1.pdfFigure 1: major steps of friction stir processing [2]

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