Influence of Welding Sequence on Residual Stress and Distortion in

Rectangular Welding of 6061 Aluminum Alloy

Yi Jie1, 2, 3, a, Li Can3 and Zhonggang Sun1

1Hunan Industry Polytechnic

2State Key Laboratory Of Advanced Design And Manufacturing Vehicle Body

3College of Materials and Engineering of Hunan University

aemail:ejay2011@sina.com

Key words: Aluminum alloy; Finite element; Welding sequence; Welding distortion

Abstract: This paper presented a detailed finite element simulation on the basis of elastic-plastic

method combined with thermo-mechannical coupling algorithm，and the software abaqus was used

for the welding simulation of thin-walled 6061-T6 aluminum. The residual stress and distortion

with various types of welding sequence were investigated and the optimal welding sequence was

gained through comparison and analysis. The results showed that the maximum residual stress on

the plane of the welds was tensile stress after welding in a rectangular. The method of symmetry

welding got smaller residual stress which could enhance the stability of the weldments, and starting

from a longer welding path got smaller residual distortion of aluminum alloy.

1. Introduction

Wrought aluminum alloy 6061 own the property of middle strength , good processability and

welding performance. And It can be welded by almost all kinds of welding methods[1]. Moreover,

tungsten electrode argon arc welding( TIG welding) is broadly used industrial process for thin

aluminum plate owing to better welding quality and easy operation.

The welding of Aluminum alloy needs a large heat power, a concentrated heat source and good gas

protect environment with the property of thermal conductivity and thermal expansion coefficient.

During the welding process, welding residual stress and deformation occur due to the highly

centralized heat input, rapid heating and cooling of the weld seam and the surrounding area uneven

expansion and contraction. And it can be reduced effectively by reasonable welding sequence. It is

shown that welding stress and deformation can be simulated and predicted by the finite element

method[2] . Softening phenomenon of 6061 aluminum alloy is firstly introduced into the finite

element analysis by Wang Zongmao[3], to improve accuracy. In order to adapt to the complex

welding structure and save the calculation time, inherent strain method was used by Ding Zhenbin

in the simulation of different welding sequences of residual stress and deformation of hull and

obtained the minimum deformation welding sequence[4]. The research of different welding

sequence of T welding joint was studied by Liam to obtained the best welding sequence and they

discuss the influence of welding stress and deformation exerting on the mechanical properties[5].

Sattari-Far [6] used 3D coupled thermo-mechanical method to simulate of residual stress and

deformation of cylinder parts on different welding sequences and acquire the optimum welding

project.

Advanced Materials Research Vol. 668 (2013) pp 890-897Online available since 2013/Mar/11 at www.scientific.net© (2013) Trans Tech Publications, Switzerlanddoi:10.4028/www.scientific.net/AMR.668.890

All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of TTP,www.ttp.net. (ID: 130.126.32.13, University of Illinois, Urbana, United States of America-28/09/13,16:10:12)

The simulation of deformation using thermal elastic plastic finite element method ,which takes

account of many material nonlinear factors, makes results more directly and easy to facilitate

comparison analysis. The numerical simulation of welding sequence optimization research mainly

concentrates in the multi-channel parallel seam welding. now this paper study the simulation of

rectangular weld ( four weld in rectangular distribution ) of 6061-T6 aluminum alloy thin wall using

ABAQUS software to analyse the effect of welding sequence to welding stress and deformation to

formulate reasonable welding sequence and to improve the structural stability[7-8].

2. Establishment of finite element model

2.1 Model condition

Fig 1 shows aluminum alloy rectangular weld physical model, The rectangular pipe,with the size of

30 mm×40 mm×150 mm, is welded with 70 mm× 90 mm× 5 mm bottom plate, ,and the material of

both of them is 6061-T6 aluminum alloy. Tungsten argon arc welding was used with welding

voltage 10 V, current 100 A, heat source moving speed 0.003 m/s, heat efficiency of welding arc

0.6.

Fig 2 is rectangular weld finite element mesh model with hexahedral element mesh.due to the

temperature gradient of welding zone larger, it should be subdivide the weld grid as small as

possible to less than 2 mm to improve accuracy. The grid model contains 16216 common unit

number and the number of nodes is 24744.

Fig.1 Physical model of aluminum welding

Fig.2 Model of finite element and boundary

conditions

2.2 Heat source selection

Welding heat source can be divided into surface and volume distribution.Gauss and double elliptic

distribution heat source is commonly used surface distribution heat source and ellipsoid and double

ellipsoid heat source because aluminum alloy has large thermal conductivity and thermal

capacity[9] , welding of aluminum needs a heat source with concentrated energy to prevent large

energy loss, so ellipsoidal heat source was used as welding source[10].

=),,,(q tzyx[ ]

−∂+−

−

−2

2

2

2

2

2

c

)(3exp

b

3exp

aexp

ππabc

Q36 tvzyx （1）

In the formulation, vwelding speed,Q as energy input, t as heat transfer time, a,b,c as the size of

axis of ellipsold ,respectively equals to 1.9 mm,3.2 mm,2.8 mm; ∂ as lag time of welding heat

source, x, y, z as the three-dimensional coordinate system.

Advanced Materials Research Vol. 668 891

2.3 Material thermal physical parameters

The property of material is assumed to be isotropic and the thermal physical parameters is a

function of the temperature[11], which has a large influence on the simulation result. due to lack of

high temperature parameter, parameter at a part of temperatures were given in table 1 and the rest of

the vacant part can be obtained by linear interpolation method.

2.4 Boundary condition

Room temperature is setted as 20 ℃ in temperature field analysis. The heat exchange of

components and ambient environment is conducted by convective and radiation in the process of

welding and the effect of radiation can be Coupled to the convective heat transfer and the

convective heat transfer coefficient is assumed as 80 W (m ° C)

Tab.1 Material parameters of 6061-T6 aluminum at different temperatures

Tempera-

ture

/℃

Heat

conduction

coefficient

/W(m℃)1−

Specific

heat

/J(Kg℃)1−

Density

/Kg(m)3−

Coefficient of

thermal

expansion/ µ (℃)1−

Modulus of

elasticity/GPa

Yield

strength/MPa

Shear

modulus/GPa

20

93.3

204.4

260

371

482.2

162

177

192

201

217

226

945

978

1028

1052

1104

1136

2700

2685

2657

2657

2630

2602

23.45

24.61

26.6

27.56

29.57

31.71

68.54

66.19

59.16

53.99

40.34

20.2

274.4

264.6

218.6

159.7

36.84

10.49

6.854

6.619

5.916

5.399

4.034

2.02

In the analysis of Stress field, the displacement boundary conditions is exerted in the plane of

symmetry,as shown in Figure 2,in which the parallel degree of freedom is constrained at the left

side of the bottom edge and all degrees of freedom are constrained at the right,in order to prevent

rigid displacement of the weldment.

3. Operating environment of Abaqus

In the Thermal elastoplastic analysis, it is assumed that the material obeys to Von Mises yield

criterion hen yield occurs[13], in which the change of temperature-related mechanical properties,

stress and strain in small time increments can be regarded as linear and the effect of the inertial

force can be ignored. The Von Mises can be defined as equivalent stress and the yield is occurred

when equivalent stress exceeds the yield limit.

The coupling of temperature and stress field adopt indirect coupling in the process of simulation.

The heat transfer units is changed to structural units after the simulation of temperature field and the

results file of temperature field imported into the calculation of stress field as a load. Namely only

consider the temperature field corresponds to the stress field ,while the contrary effect is ignored.

The heat source is applied along the pipe at the bottom of the four sides at different sequence.

Because the moving of heat source can not be achieved in an Abaqus CAE (Complete Abaqus

Environment) interface, so Abaqus was secondary development based on Fortran language to

compile dflux heat source subroutine. The heat source is applied by definition of the start point and

moving direction at different step and the subroutine was called at the final submission of the task

manually.

892 Materials Science and Engineering II

In the calculations of stress field, the large deformation switch Nlgeom is set to open due to large

deformation occurred in welding. The initial incremental step length is set as 0.01 and the step

length is 0.1 during the cooling process. The increment step is set to automatic and Abaqus will

adjust increment step based on the the analysis of step-by-step time to speed up the calculation

process.

4. Simulation results and analysis of welding stress-strain field

Four welding program is compared to study the effect of welding sequence to residual stress, as

shown in figure 3,in which 1.2.3.4 represents welding order and the arrow indicates the direction of

welding.

(a) (b) (c) (d)

Fig.3 Schematic illustration of the four welding sequences

4.1 Stress field

The simulation result of 4 projects seems to be similar, so we adopt one case to analyse. The

distribution of equivalent stress after welding is shown in figure 4.

Fig.4 Figure of equivalent stress after welding

As we can see from figure 4, the equivalent residual stress mainly appears in the four weld area and

the right side of the bottom edge produce a larger equivalent residual stress due to all the degrees of

freedom are constrained. The minimum Equivalent residual stress occurs in the free end of the

upper pipe and a smaller equivalent residual stress occurs at the left side of bottom plate due to the

constrained translational degrees of freedom of the X and Y directions. From the result shown, we

can see that the maximum residual tensile stress happens at the welding zone while the compressive

one occurs at the area away from the weld.

Advanced Materials Research Vol. 668 893

Tab.2 Maximum residual stress of X, Y, Z direction (MPa)

Welding

solution

X Y Z

Tensile

stress

Compressive

stress

Tensile

stress

Compressive

stress

Tensile

stress

Compressive

stress

1

2

3

4

175.9

173.8

193.7

153.7

139.6

132.3

138.4

123.8

177.0

201.1

180.4

222.9

133.2

133.2

116.2

147.0

117.0

92.29

104.7

71.53

122.0

109.9

104.1

93.05

Seen from Table 2, a large residual tensile stress along X and Y directions is obtained and the value

of residual tensile and compressive stress is close along Z directions. By comparison between 1.2.3

and 4, it is shown that the maximum residual tensile stress is comparative large if the welding path

is consistent with the welding direction while it is relatively small if perpendicular. The equivalent

stress and the maximum residual stress was shown in figure 5. By comparison along three

directions, the residual stress perpendicular to weld plane is larger than it along directions at

welding plane.

1 2 3 4

150

200

250

300

350

400X

Y

Z

Equivalent stress

Stress/MPa

Solution

Fig.5 Equivalent stress and maximum stress of the three coordinate directions

By comparison of the residual stress along X andY direction, stress along Y direction is larger than

it along X direction in 2 and 4 project, while it is contrary in 1 and 3 project. It can be concluded

that the maximum residual stress is larger when the first welding path is consistent with the certain

welding direction. Moreover ,the equivalent stress in the 3 and 4 project is relatively smaller than

the first two project, which indicates that symmetrical welding can obtain small equivalent stress.

So welding parts have the capacity of good structural stability and better resistance to deformation

and not prone to yield and derorm.

4.2 Welding deformation

Take project 1 as example, the total displacement along X, Y, Z direction is shown in figure 6.

According to figure 6, the maximum total displacement occurs at the top of the pipe, while the right

side of bottom plate has no displacement owing to all degrees of freedom constrained.Meanwhile,

the left side of base plate generate a relatively large displacement due to translation motion along X

and Y direction. It is visibly that the welding structures need to be fixed by reasonable fixings to

control the deformation of some sections and directions of welding parts.

894 Materials Science and Engineering II

Fig.6 The combined displacement of X, Y, Z direction

Seen from Table 3,the bottom plate produce a displacement in the positive direction of the X axis

due to the constraint along the Y direction. positive displacement is mainly displayed along X

direction and negative deformation is much smaller than the forward deformation, while the

positive and negative deformation along Y and Z direction has no siginificant different. So take the

deformation along X axis as analysis. From the data in table 3, the positive and negative

deformation is close between project 1 and 3 and the former maximum deformation were smaller

than the latter, which indicates that the welding began from the longer the path can get a smaller

amount of deformation. both of the maximum deformation in project 1 and 2 are greater than it of

project 3 and 4, indicating that symmetrical welding can reduce the maximum amount of

deformation of the component along X direction. From the above table it can be seen the third

project gets the minimum value of forward and negative deformation in the X direction.

Tab.3 Maximum distortion of X, Y, Z direction (mm)

Welding

solution

X Y Z

Positive Negative Positive Negative Positive Negative

1

2

3

4

0.8451

1.019

0.8254

0.9883

0.07117

0.1109

0.06371

0.09232

0.3762

0.7874

0.3688

0.3288

0.3486

0.3638

0.3915

0.5898

0.3753

0.3813

0.3837

0.4535

0.2591

0.2514

0.2445

0.1822

The amount of deformation generated in the Z direction in the four scenarios are small and close

from figure 7, so the overall deformation of structure can be analysed through the amount of

deformation along X and Y directions. The value of the first and second program is larger than it of

the second and forth evidently, indicating that welding start from the longer weld path get a small

amount of residual deformation. meanwhile ,the equivalent stress produced in the third and forth

project is small and has a reliable structure. In conclusion, project 3 is the best welding method.

1 2 3 ?0.4

0.6

0.8

1.0

1.2

X

Y

Z

Deformation/mm

Solution

Fig.7 Maximum distortion of the three coordinate directions

Advanced Materials Research Vol. 668 895

4.3 Results Analysis

Welding residual tensile stress is mainly occurred in the direction along the weld and therefore

tensile residual stress after the multi-pass weld occured mainly in the welding plane. In the

rectangle welding process, the residual stress generated in the first welding path direction is greater

than the rest directions

Seen by the results of the deformation field, the welding deformation mainly appears in the welding

plane. The values of deformation with different sequences have a large difference. The overall

deformation of the first and third are larger than it of the second and forth one, stating that different

welding sequences has a large influence on the deformation of the weldment. So reasonable

welding sequence can be choosed to optimize residual stress and deformation.

From the simulation results, the maximum residual stress and equivalent stress along Z direction in

the four programs differs greater, which respectively is 134.42 MPa and 71.9 MPa. While ,the

maximum deformation along X direction is 0.4264 mm and differs greater.

5. Conclusion

(1) In the case of rectangular multi-pass welding, the residual tensile stress is generally generated on

the seam plane and the tensile residual stress and the compressive residual stress generated in the

direction perpendicular to the weld plane is little difference; welding deformation mainly occurred

in the weld plane.

(2) The first welding path affect the value of the residual stress in a particular direction during

rectangular welding. Therefore, the residual stress can be improved by choosing the welding path to

a specific direction.

(3) For rectangular welding, symmetrical welding can enhance the stability of the structure and the

weldment is not prone to deform; the amount of welding deformation can be reduced effectively if

welding start from the longer path.

Reference

[1] Wangfu Huang，Jingang Huang. Aluminum ang aluminum welding guide[M].Changsha：

Hunan Science and Technology Press，2004, 56-61.

[2] C.Liu, J.X.Zhang, C.B.Xue. Numerical investigation on residual stress distribution and

evolution during multipass narrow gap welding of thick-walled stainless steel pipes[J]. Fusion

Engineering and Design, 2011, 86:288-295.

[3] Zongmao Wang，Jianping Wang，Fei Wu. Welding deformation of 6061 aluminum alloy

numerical analysic[J]. Shandong machinery，2004(6):36-38.

[4] Zhenbin Ding，Xiaodan Jia，Tu guang Liu. The effect of welding sequence to deformation of

hull[J]. Shipbuilding of China，2010,51(S1):81-85.

[5] Liam Gannon, Yi Liu, Neil Pegg, et al. Effect of welding sequence on residual stress and

distortion in flat-bar stiffened plates[J]. Marine Structures, 2010, 23:385-404.

[6] I.Sattari-Far, Y.Javadi. Influence of welding sequence on welding distortions in pipes[J].

International Journal of Pressuer Vessels and Piping, 2008, 85:265-274.

896 Materials Science and Engineering II

[7] S D Ji, H Y Fang, X S Liu, Q G Meng. Influence of a welding sequence on the welding residual

stress of a thick plate[J]. Modeling and Simulation in Materials Science and Engineering, 2005,

13:553-565.

[8] Tso-Liang Teng, peng-Hsiang Chang, Wen-Chen Tseng. Effect of welding sequences on

residual stresses[J]. Computers and Structures, 2003, 81:273-286.

[9] Chuansong Wu.Welding thermal process and the shape of welding pool [M].Beijing：

Machinery Industry Press，2007, 22-27.

[10] Liguo Zhang，Shude Ji，Hongyuan Fang.The effect of welding sequence to T welding

residule stress field[J].Journay of Machanical Engineering,2007, 43(2):234-238.

[11] Hejing Chen.Study on prediction methods of buckling deformation and residual stresses for

FSW[D].Tianjin:Tianjin University,2007.

[12] Song Zhang，Chunhua Zhang，Ning Zhang.Simulation and experimental investigationa of

laser cladding temperature field on 6061 Al alloy[J].Transaction of the China welding

institution，2007, 28(10):1-4.

[13] Zhenhua Huang.Optimization study on Welding Sequence of the Nautical Profile Butt

Welding[D].Dalian:Dalian University of Technology,2009.

Advanced Materials Research Vol. 668 897

Materials Science and Engineering II 10.4028/www.scientific.net/AMR.668 Influence of Welding Sequence on Residual Stress and Distortion in Rectangular Welding of 6061

Aluminum Alloy 10.4028/www.scientific.net/AMR.668.890