Upload
danghanh
View
215
Download
0
Embed Size (px)
Citation preview
http://www.iaeme.com/IJMET/index.asp 173 [email protected]
International Journal of Mechanical Engineering and Technology (IJMET) Volume 8, Issue 12, December 2017, pp. 173–183, Article ID: IJMET_08_12_018
Available online at http://www.iaeme.com/IJMET/issues.asp?JType=IJMET&VType=8&IType=12
ISSN Print: 0976-6340 and ISSN Online: 0976-6359
© IAEME Publication Scopus Indexed
DETERMINATION OF MECHANICAL
PROPERTIES OF FRICTION STIR WELDED
JOINT FOR ALUMINIUM ALLOY 6351 (HE-30)
B.Praveen Kumar, N.Samba Siva Rao and M.Mohith
Asst. Prof, Talla Padmavathi College of Engineering
P.Srikanth
Professor, KITS Warangal
ABSTRACT
Friction stir welding is a solid state welding process this process uses non-
consumable tool to generate frictional heat in the abutting surfaces. The welding
parameters such as tool rotational speed, welding speed, axial force etc., and the tool
pin profile plays a major role in deciding the weld quality. The main objective of
thesis is investigation of mechanical properties of friction stir welded aluminium alloy
6351 (HE30). Analysis of effect of tool pin profile on mechanical properties of
aluminium alloy. Heat treatment improves tensile strength, ductility, hardness.
Tapered Cylindrical tool pin profile gives higher tensile strength. Square tool pin
profile gives higher hardness. Triangular tool pin profile gives higher percentage of
elongation.
Keywords: Friction Stir Welded, Mechanical Properties, Aluminium Alloy 6351
Cite this Article: B.Praveen Kumar, N.Samba Siva Rao, M.Mohith and P.Srikanth,
Determination of Mechanical Properties of Friction Stir Welded Joint for Aluminium
Alloy 6351 (He-30), International Journal of Mechanical Engineering and Technology
8(12), 2017, pp. 173–183.
http://www.iaeme.com/IJMET/issues.asp?JType=IJMET&VType=8&IType=12
1. INTRODUCTION
Friction Stir welding (FSW) is a novel welding technique invented by the welding Institute
(TWI) in 1991 (Cary H.B., 1979) [1] FSW is actually a solid State joining process that is a
combination of extruding and forging and is not a true welding process. FSW is a derivative
of conventional friction welding. The FSW is a derivative of conventional friction welding.
The FSW process involves the translation of a rotating cylindrical tool along the interface
between two plates. The weld is formed by the deformation of the material at temperatures
below the melting temperature. FSW does not create a Heat effected Zone nor does it use
welding consumables. Since traditional heating methods are not employed. The properties of
the metal in the joined area are higher than those from any other known welding process and
distortion is virtually eliminated (Weisheit A at all, 1998, Juttner, 1998) [2].
Determination of Mechanical Properties of Friction Stir Welded Joint for Aluminium Alloy 6351
(He-30)
http://www.iaeme.com/IJMET/index.asp 174 [email protected]
2. LITERATURE REVIEW
2.1 Friction Stir Welding in 1XXX Series Aluminium Alloys
Sato Y.S. et all (2003) studied a friction stir welding of ultrafine grained A1 alloy 1100
produced by accumulative roll bonding. FSW resulted in reproduction of fine grains in the stir
zone and small growth of the ultrafine grains of the material just outside the stir zone. FSW
suppressed large reductions of hardness in the material, although the stir zone and the TMAZ
experienced small reductions of hardness due to dynamic recrystallization recovery.
Consequently, FSW effectively prevented the softening in the alloy.
2.2 Friction Stir Welding in 5XXX Series Aluminium Alloys
Peel M. (2003) studied a microstructure, mechanical properties and residual stresses as a
function of welding speed in aluminium AA5083 friction stir welds. It has been found that the
weld properties have been dominated by the thermal input rather than the mechanical
deformation by the tool. The main results have been obtained that the recrystallization results
in the weld zone having considerably lower hardness and yield stress than the parent AA5083.
During tensile testing, almost all the plastic flow occurs within the recrystallized weld zone.
The peak longitudinal stresses increase as the traverse speed increases. This increase is
probably due to steeper thermal gradients during welding and the reduced time for stress
relaxation to occur. The base material is in an extremely work hardened state and this is
reflected in the hardness profiles.
3. MATERIAL SELECTION AND TOOL DESIGN
Material selection in Friction Stir welding is an important role, the aluminium alloys have
gathered wide acceptance in the fabrication of light weight structures requiring a high strength
to weight ratio and good corrosion resistance. Compared to the fusion welding processes that
are routinely used for joining structural aluminium alloys.
3.1 Friction Stir welding tool pin profiles:
Pin profile plays a crucial role in material flow and in turn regulates the welding parameters
of the FSW process. Friction stir welds are characterized by well-defined weld nugget and
flow contours. Almost spherical in shape, these contours are dependent on the tool design and
welding parameters and process conditions used.
Figure 1
B.Praveen Kumar, N.Samba Siva Rao, M.Mohith and P.Srikanth
http://www.iaeme.com/IJMET/index.asp 175 [email protected]
4. EXPERIMENTAL DETAILS
Details of base metal composition, friction stir welding processes, mechanical testing and
metallographic techniques are described in the following.
4.1. Base metal
The aluminium alloy studies in the present work are 5 mm thick plate of AA 6351 (HE30)
whose chemical composition and mechanical properties are listed in table 1 and 2.
Table 1 Chemical composition (Wt.%) of 6351 (HE 30) Aluminium alloy.
Cu Mg Si Fe Mn Zn Cr Ti Others
0.1 0.4-1.20 0.60-1.3 0.60 0.4-1.0 0.1 0.25 0.20 0.20
Table 2 Mechanical Properties:
Mechanical Property UTS (N/mm2) YS (N/mm
2) % of Elongation
6351 (HE 30) 285 240 8
The rolled plates of 5 mm thickness, AA6351 (HE30) aluminium alloy, have been cut into the
required size (100x60 mm) by power hacksaw cutting. Square butt joint configuration has
been prepared to fabricate FSW joints. The initial joint configuration is obtained by securing
the plates in position using fixture and mechanical clamps. The direction of welding is normal
to the rolling direction. Single pass welding procedure has been followed to fabricate the
joints. Non-consumable tools made of high speed steel (HSS) have been used to fabricate the
joints as shown in fig.2. An indigenously designed and developed CNC milling machine has
been used to fabricate the joints.
Figure 3 FSW tool dimensions and shapes
Determination of Mechanical Properties of Friction Stir Welded Joint for Aluminium Alloy 6351
(He-30)
http://www.iaeme.com/IJMET/index.asp 176 [email protected]
Figure 4 Welded Sample by Tapered Cylindrical and Triangular Tool
Table 3 Welding parameters during FSW Operation on CNC milling machine
Sample Material Type of tool Speed
RPM
Feed
mm/min.
% of
spindle
load
Pin
depth
(mm)
Opera-
tion time
(min)
Sample 1 6351 Tapered
Cylindrical 800 14 15-20 4.7 8.8
Sample 2 6351 Triangular 1000 12 20-25 4.7 10.5
Sample 3 6351 Square 1200 10 20-25 4.7 11.9
5. TESTING METHODS
In this investigation mechanical properties such as yield strength, tensile strength and
percentage of elongation of FSW joints have been evaluated.
5.1. Tensile Test
American Society for Testing of Materials (ASTM) guidelines are followed for preparing the
test specimens. Test has been carried out in 400 KN, Universal Testing Machine. The
specimen finally fails after necking and load versus displacement has been recorded. The
ultimate tensile strength and percentage of elongation have been evaluated for tapered
cylindrical tool pin as shown in Table 4, Triangular tool pin as shown in Table 5 and square
tool pin as shown in Table 6.
Table 4 Tensile strength obtained by Tapered Cylindrical tool pin profile
PWHT UTL(N) UTS (N/mm2) Yield load (N)
Yield Stress
(N/mm2)
% of
Elongation
Without HT 20560 179.104 19640 171.095 2.860
With HT
(Aircooling) 25134 300.341 24640 250.125 1.00
Base Metal 23000 285.00 22000 240.00 8
B.Praveen Kumar, N.Samba Siva Rao, M.Mohith and P.Srikanth
http://www.iaeme.com/IJMET/index.asp 177 [email protected]
Figure 5 Y-Axis (N) Vs. X-Axis disp. (mm) for tapered cylindrical tool pin
Figure 6 Y-Axis (N) Vs. X-Axis disp. (mm) for triangular tool pin
Table 5 Tensile strength obtained by Triangular tool pin profile
PWHT UTL(N) UTS
(N/mm2)
Yield load
(N)
Yield Stress
(N/mm2)
% of
Elongation
Without HT 25560 258.819 24000 242.206 1.220
With HT
(Aircooling) 30560 352.132 29000 320.00 1.00
Base metal 28000 285.00 26000 240.00 8
Table 6 Tensile strength obtained by square tool pin profile
PWHT UTL(N) UTS (N/mm2) Yield load (N)
Yield Stress
(N/mm2)
% of
Elongation
Without HT 18000 171.00 17000 150.00 1
With HT air
cooling 25000 228.00 24000 215.0 1
Base Metal 22000 285.00 20000 240.00 8
Determination of Mechanical Properties of Friction Stir Welded Joint for Aluminium Alloy 6351
(He-30)
http://www.iaeme.com/IJMET/index.asp 178 [email protected]
5.2. Brinnel Hardness Test
Table 7 Hardness varying with Tapered Cylindrical tool pin profile.
Distance from weld
centre, mm
Brinnel hardness
Without HT With HT (AC) Base metal
0
5
10
15
20
84.9
80.2
80.2
80.0
82.0
86.0
82.0
85.0
82.0
84.0
80
78
78
79
78
Table 8 Hardness varying with Triangular tool pin profile.
Distance from
weld centre, mm
Brinnel hardness
Without HT With HT (AC) Base metal
0
5
10
15
20
84.9
81.0
80.3
80.0
81.0
86.0
82.0
84.0
82.0
84.0
80
78
78
79
78
Table 9 Hardness varying with Square tool pin profile.
Distance from
weld centre, mm
Brinnel hardness
Without HT With HT (AC) Base metal
0
5
10
15
20
85
82
81
81
82
84
83
84
82
83
80
78
78
79
78
6. RESULTS AND DISCUSSIONS
Hardness
Recent investigations show that the bonded structure has periodic variation in grain size, a
clearly defined difference in both particle distribution and also hardness variation. Fig.4
presents Rockwell hardness results from straight lines at Z=00 mm on vertical transverse
cross section in FSW for AA 6351. The two welds exhibit a W-shaped hardness distribution
that is characteristic of many friction stir welds in precipitation hardening aluminium alloys.
Here the hardness data shows that the weld nugget is significantly harder than the thermo
mechanically affected region immediately outside the nugget boundary. Moving outwards
from the nugget centerline towards the advancing side of the weld, the profiles encounter the
distance minimum at location of 5 mm.
Tapered Cylindrical tool pin profile
At the weld centre the hardness is more in case of PWHT for air cooling (24 hours) than base
metal and others as shown in fig 7 for Tapered Cylindrical tool profile due to sufficient time
allowed to obtain fine grain structure. At the interface also, the hardness is more than base
B.Praveen Kumar, N.Samba Siva Rao, M.Mohith and P.Srikanth
http://www.iaeme.com/IJMET/index.asp 179 [email protected]
metal others due to tool pin rotate uniformly in the metal with very fast and at interface grains
are properly adjusted with adjacent region.
Figure 7 Hardness variation from Weld centre for Tapered Cylindrical Tool pin
Triangular tool pin profile
At the weld centre the hardness is more in case of PWHT for air-cooling (24 hrs.) than base
metal and others as shown in fig.8. For triangular tool pin profile due to sufficient time
allowed to obtain fine grain structure. AT the interface, the hardness is approximately equal to
hardness without heat treatment. Due to tool pin is not rotate uniformly in the metal with low
speed. At the interface, the metal is cut by tool because sharp edges and it gives poor mixing.
Figure 8 Hardness variation from Weld centre for Triangular tool pin
Square tool pin profile
Determination of Mechanical Properties of Friction Stir Welded Joint for Aluminium Alloy 6351
(He-30)
http://www.iaeme.com/IJMET/index.asp 180 [email protected]
At the weld centre the hardness is more in case of without heat treatment than base metal and
others shown in Fig.16. For square tool pin profile. At the interface, the hardness is more in
cse of with heat treatment for air tooling than others, but it is more than base metal due to tool
pin is not rotate uniformly in the metal with low speed. At the interface, the metal is cut by
tool because sharp edges and it gives poor mixing. Due to sharp edges, the metallic bond is
poor and it loses hardness in heat treatment condition.
Figure 9 Hardness variation from Weld Centre for square tool pin
Comparison of tool pin profile
The hardness is high in weld zone in heat treatment condition (Air cooling) in Tapered
Cylindrical tool pin and in triangular tool pin and the hardness is high in weld zone in square
tool pin without heat treatment condition. In all the condition the hardness is higher than base
metal.
Tensile results for welded specimen
The welded sample of AA 6351 has a ultimate tensile strength in all conditions is less than the
base metal. The total elongations and strains to fracture are similar in both nuggets, interface
and base metal. Overall, it can be stated that the tensile properties of the weld nuggets and of
the corresponding base metals are very similar to each other.
Tapered Cylindrical tool pin profile
The tensile strength is approximately equal to base metal in heat treated condition with air
cooling and tensile strength is poor in without heat treatment. Due to air cooling for 24 hrs.,
the grain settle in their positions properly because sufficient time allowed and tool rotate
uniformly with high speed in the metal, the welded metal gives high tensile strength. Tensile
strength of welded sample is poor than the base metal due to rotational speed of tool pin
profile is low i.e. 800 rpm. Due to that the bond integrity is poor in weld metal as shown in
figure10.
B.Praveen Kumar, N.Samba Siva Rao, M.Mohith and P.Srikanth
http://www.iaeme.com/IJMET/index.asp 181 [email protected]
Figure 10 Tensile strength varying with heat treatment process for Tapered cylindrical tool
Triangular tool pin profile
The tensile strength of friction stir welded sample using triangular tool in without heat treated
condition is less than base material and tensile strength is height than in heat treated condition
with air cooling. In heat treated condition with air cooling due to improper mixing of weld
metal because sharp edges of pin profile. Tensile strength of welded sample is poor than the
base metal due to rotational speed of tool pin profile is low i.e. 1000 rpm. Due to that the
bond integrity is poor in weld metal as shown in Fig. 11.
Figure 11 Tensile Strength varying with Heat treatment process for Triangular Tool
Square tool pin profile
The tensile strength of friction stir welded sample using square tool inwith heat-treated
condition is less than base material and the tensile strength is higher than in without heat
treated condition due to sharp edge and low speed. The tensile strength is poor in without heat
treated condition. So heat treatment process is required for square tool. Tensile strength of
Determination of Mechanical Properties of Friction Stir Welded Joint for Aluminium Alloy 6351
(He-30)
http://www.iaeme.com/IJMET/index.asp 182 [email protected]
welded sample is poor than the base metal due to rotational speed of tool pin profile is low i.e.
1200 rpm. Due to that the bond integrity is poor in weld metal as shown figure 12.
Figure 12 Tensile strength varying with Heat treatment process for square tool pin
Comparison of tool pin profile
Tensile strength is high in case of Tapered Cylindrical tool with heat treatment for air cooling
and tensile strength is high in case of triangular tool without heat treatment. In case of square
tool the tensile strength is high with heat treatment in air cooling.
7. CONCLUSIONS
The hardness is high in weld zone in heat treatment condition (Air Cooling) in Tapered
circular tool pin and in triangular tool pin and the hardness in high in weld zone in square tool
pin without heat treatment condition. In all the condition the hardness is higher than base
metal. Tensile strength is high in case of Tapered Circular tool with heat treatment for air-
cooling and tensile strength is high in case of triangular tool without heat treatment. In case of
square tool the tensile strength is high with heat treatment in air cooling.
REFERENCES
[1] Gary H.B., 1979, Modern Welding Technology Prentice Hall, inc., Engelwood Cliffs,
New Jersey, PP223
[2] Juttners, Fabr. 1998, Weld met; 66:11
[3] Dawis C.T. and Thomas W.M., 1996, Friction Stir Process Welds Aluminium Alloys, a
New Friction Welding Technique Allows Easy Welding of normally difficult to join
materials, Welding Journal, 75 (3), PP 41.
[4] Lee W.B., Yeon Y.M. and Jung S.B., 2003. The improvement of Mechanical properties of
friction stir – welded A 356, PP. 154-159.
[5] Benavides S., Li Y., Murr L.E., Brown D. and Mcclure JC, 1999 Low Temperature
Friction Stir Welding of 2024 Aluminium, Scripta Materialia, Vol. 41. No.8 PP.809-815.
[6] Fonda R.W., Bingert J.F. and Colligan K.J., 2004, Development of Grain Structure during
Friction Stir welding, Scripta Materialia 51, PP.243-248.
B.Praveen Kumar, N.Samba Siva Rao, M.Mohith and P.Srikanth
http://www.iaeme.com/IJMET/index.asp 183 [email protected]
[7] Dickerson T.L. and Przy Datek J. 2003, Fatigue of friction stir welds in Aluminium alloys
that contain Root Flaws International Journal of Fatigue, 25, PP 1399-1409.
[8] Liu G., Murr L.E., Niou C.S., Mcclure J.C. and vega F.R., 1997, Mcrostructural aspects of
the Friction Stir Welding of 6061 – T6 Aluminium, Scripta Materialia Vol.37, No.3, PP
355-361.
[9] Lee W.B., Yeon Y.M., Jung S.B., 2003, The Joint Properties of Dissimilar Formed Al
Alloys by Friction Stir welding according to the fixed location of materials Scrpta
Materialia, 49, PP 423-428.
[10] Cavaliere P., Nobiler, Panella F.W. and Squillace A., 2006, Mechanical and
Microstructural Behaviour of 2024-7075 Aluminium Alloy Sheets Joined by Friction Stir
Welding, International Journal of Machine Tools & Manufacture, 46, PP.588-594.
[11] JATA K.V. and SEMIATIN S.L., 2000, Continuous Dynamic Recrystallization During
Friction Stir Welding of High Strength Aluminium Alloys Scripta Materialia, 43, PP 743-
749.
[12] LI Y, Murr L.E. and Mcclure J.C., 1999, Flow visualization and Residual Microstructures
Associated with the Friction – Stir – Welding of 2024 Aluminium to 6061 Aluminium
materials Science and Engineering, A271, PP 213-223.
[13] Chao B.Y.J., Wang Y and Miller K.W., 2001, Effect of Friction Stir welding on Dynamic
Properties of AA 2024-T3 and AA 7075-T.7351 Journal of material processing and
manufacturing, 7(2), PP.215-233.
[14] Chen C.M. and Kovacevic R., 2004, Joining of Al 6061 to ALSI 1018 Steel by combined
effects of Fusion and solid state welding, International Journal of Machine Tools and
Manufacture.
[15] Sreeharan B N, Dr. Kannan T and Aravind P, Process Optimization of GMAW over
Aa6351 Aluminium Alloy Using Ann, International Journal of Civil Engineering and
Technology, 8(9), 2017, pp. 208–218.
[16] Ragip Hadri and Ali Muriqi, Aluminum Alloys and Behavior under Cyclic Loading in
Joints of Truss Structures, International Journal of Civil Engineering and Technology,
8(11), 2017, pp. 746–752
[17] R. MuthuVaidyanathan, MahaboobPatel, N. SivaRaman and D. Tedwors, Effects of
Process Parameters on Friction Stir Welding of 6063 Aluminum Alloy, International
Journal of Design and Manufacturing Technology (IJDMT), Volume 6, Issue 1, January -
April (2015), pp. 01-09