Post on 24-Jun-2020
Tensile behaviour of AA 5052-AA
6063 lap joints through friction
stir spot welding process
Dr.J.Srinivas
Associate Professor, Mechanical Engg.,
NIT Rourkela
Presentation outline
• Introduction
• Methodology
• Results and Discussion
• Conclusions
• References
Introduction • Currently, for assembling aluminum alloy parts, resistance
spot welding, riveting and laser spot welding are employed
intensively.
• All these conventional processes have disadvantages such
as poor weld strength, large heat residual stress and
distortion, tool consumption during joining and formation of
different defects.
• In the recent years, the new spot welding process was
developed called friction stir spot welding (FSSW).
• Friction stir spot welding (FSSW) is a modification of the
friction stir welding (FSW) process that can effectively
replace the resistance spot welding technique used in the
automotive industry. FSSW exhibits several advantages in
welding dissimilar materials.
FSSW background
• In 2000, FSSW has been proposed to create a spot weld
using frictional heat.
• The bonding between the two thin sheets was mainly
achieved by the frictional heat and high applied pressure.
• In FSSW, under the tool, there are
(a) stir zone (SZ),
(b) heat-affected zone (HAZ)
(c) thermomechanically affected zone (TMAZ)
• SZ has finer equaixed grains than the TMAZ.
Principle of FSSW• A non-consumable rotating tool is plunged into the workpieces.
• The maximum penetration of the tool into the workpiece, from the
point that the pin is tangent to the workpiece surface is called plunge
depth.
• Upon reaching to the specified plunge depth, the rotating tool is held
in that position for a predetermined time.
• Subsequently, the rotating tool is retracted from the welded joint
leaving behind a friction stir spot weld.
Factors affecting the mechanical properties
• The mechanical properties of FSSW joints depend
on the amount of generated heat, material
plasticization around the pin and weld geometry.
• All of these factors can be controlled by the main
process parameters such as plunge depth, dwelling
time and rotating velocity.
Recent works on FSSWS.No Authors Year Work carried-out
1 Kai Chen; Xun Liu; Jun NiJ. Manuf. Sci. Eng 139(8), 081016 (May 25, 2017
2017 FSSW of Aluminum and steel wasillustrated and investigated failureusing a lap shear tests whichrevealed that cross nugget failure isthe only failure mode
2 Yufeng Sun, Hidetoshi Fujii, Shijie Zhu, Shaokang GuanJournal of Materials Processing Technology, 264, 2019, 414-421
2019 Illustrated 3 sheet friction stir spotwelding of Aluminum alloy
3 Q. Chu, W. Y. Li, X. W. Yang, J. J. Shen, W. B. WangJournal of Materials Science & Technology, 34, 2018, 1739-1746
2018 Proposed FSSW of Al-Li alloys with probeless tool
4 Isam Jabbar Ibrahim, GuneyGuven YapiciJournal of Manufacturing Processes, 35, 2018, 282-288
2018 Joint of 6061-T6 and 2024-T3 aluminum alloys was prepared with intermediate layer t avoid the key hole defect.
Objectives of present work• Preparation of the lap joints of two dissimilar aluminum
alloys AA5052 and AA6063 with specially prepared tool.• Samples with varying depth of cut, tool rotation and plunge
time.• Lap shear strength is measured for all the specimen using a
computerized universal testing machine.• The transient temperature distribution on either side of
weld nugget is also measured using dual Laser Infraredthermometer.
• The results of welded lap joints at different parameters arecompared for two cases where AA5052 samples are kept atthe top and bottom faces of AA6063 samples separately.
• A generalized regression model is developed to find lapshear and temperaturesat the weld nugget as a function ofinput variables.
Experimental approach• AA5052 and AA 6063 aluminum alloy in the form of a
sheet with 2mm thickness was used.
• Lap-shear configuration has been utilized, which was
made by two 30mmx100mm sheets.
• Also, a 15mmx30mm area has been used for the
overlap.
• The welding overlap samples are prepared as per AWS
standards by using a square headed pin profiled
shoulder tool on vertical milling machine with variation of
plunge time and rotational speed of the tool.
Chemical compositions
S.no. Element Percentage
1 Si 0.2-0.6
2 Fe 0.0-0.35
3 Cu 0.0-0.1
4 Mn 0.0-0.1
5 Mg 0.45-0.9
6 Zn 0.0-0.1
7 Ti 0.0-0.1
8 Cr 0.1 max
9 Al balance
AA6063S.no. Element Percentage
1 Cu 0.1
2 Mg 2.2-2.8
3 Si 0.25
4 Fe 0.4
5 Mn 0.1
6 Zn 0.1
7 Ti -
8 Cr 0.15-0.35
9 Al Balance
AA5052
Tool geometry
S.No. Specifications Dimensions (in mm)
1 Length of the tool 100
2 Width of the square pin 3
3 Height of square pin 2.2, 2.8, 3.2 and 3.5
4 Diameter of the shoulder 9
5 Diameter of the head 12
6 Length of the shank portion 55
7 Height of the shoulder 2
8 Length of the head portion 40
The welding tool was made from hot-work tool steel of H13,
which was tempered and hardened to 45–48 HV
Temperature Measurements• There are 2 sets of dissimilar samples considered: (1) AA5052
on top and AA6063 on bottom (2) AA6063 on top and AA5052on bottom. Total there are 18 samples prepared.
• During the spot welding, with the help of Dual Laser InfraredThermometer, the temperatures on the areas that are along withthe spot are observed on each specimen.
• Along with the temperatures, the plunge time and speed arerecorded.
45
50
55
60
65
1 2 3 4 5 6
Tem
per
atu
re in
deg
C
position
Lap shear test• For the evaluation of the joint strength, mechanical test samples
are prepared and tested under a tensile load at a displacement
rate of 0.025 mm/s utilizing an Instron mechanical test frame (100
t) where force and displacement values were captured.
• Standard metallographic sample preparation techniques including
grinding, polishing and etching were utilized. Samples were etched
with Keller’s reagent (190 ml H2O, 5 ml HNO3, 3 ml HCl and 2 ml
HF).
• Scanning electron microscopy (SEM) were used for characterizing
the weld zones.
Results and Discussion• Input process parameters:
1.Speed : 760 rpm, 1130 rpm, 1340 rpm, 2000 rpm
2. Plunge time: randomly measured
LAP JOINT
SPECIFICATIONS
SPEED(rpm) PLUNGE
TIME(sec)
ULTIMATE
TENSILE
STRENGTH(MPa)
MAXIMUM
LOAD (kN)
TENSILE STRESS AT
YIELD (OFFSET
O.2%) (MPa)
AA5052-AA6063 2000 13.92 26.76 1.12 14.3475
AA5052-AA6063 1340 14.36 22.93 1.30 16.54647
AA5052-AA6063 760 15.92 21.54 1.26 16.32897
AA5052-AA6063 1130 15.21 19.84 1.16 13.45675
AA5052-AA6063 760 16.29 13.39 1.05 17.13521
AA5052-AA6063 2000 16.37 18.54 1.65 14.56456
AA5052-AA6063 1340 15.15 19.32 1.83 16.59823
AA5052-AA6063 1130 14.17 12.54 1.45 14.52897
AA5052-AA6063 760 15.19 13.32 1.52 14.62197
Stress-strain diagram
760 rpm with two different plunge times: 16.29 seconds and 15.19 seconds
Test results with AA6063 sample above AA5052 sample
LAP JOINT
SPECIFICATIONS
SPEED(rpm) PLUNGE
TIME(sec)
ULTIMATE
TENSILE
STRENGTH(MPa)
MAXIMUM
LOAD (kN)
TENSILE STRESS
AT YIELD (OFFSET
O.2%) (MPa)
AA6063-AA5052 2000 14.28 13.20 1.34 12.30765
AA6063-AA5052 1340 15.23 13.42 1.72 11.19623
AA6063-AA5052 760 16.52 11.33 1.42 17.98543
AA6063-AA5052 1130 16.41 13.63 1.36 18.35867
AA6063-AA5052 760 14.48 12.25 1.22 16.65208
AA6063-AA5052 2000 16.29 16.28 1.76 14.93165
AA6063-AA5052 1340 15.28 14.42 1.23 13.98213
AA6063-AA5052 1130 14.51 18.32 1.36 17.59238
AA6063-AA5052 760 15.59 19.80 1.24 12.36891
Plunge time vs Maximum load
• Two cases at 760 rpm are considered; one withAA5052 plates on top and other with AA6063plates on top
1
1.1
1.2
1.3
1.4
1.5
1.6
15 15.2 15.4 15.6 15.8 16 16.2 16.4
Max
imu
m lo
ad (
kN)
stirring time
AA5052 plates on top surface
1.2
1.25
1.3
1.35
1.4
1.45
14 14.5 15 15.5 16 16.5 17
max
imu
m lo
ad (
kN)
plunge time in sec
AA 6063 plates on top of AA5052
Microstructure around the joint• According to the microscopic investigations, at shorter times of stirring it was
found that the joint had been produced uniformly. However, the longer times
caused more material flow and stirring, which led to more partially bonded
regions.
Conclusions
• Temperature distribution on both the sides of spot
welded region was measured using infrared
thermometer during welding. It was observed that
temperatures on 6063 side are higher.
• Static strength of friction stir spot welds of AA6063
and AA5052 alloys in the various conditions of stirring
time of welding have been investigated.
• The mechanical behavior of different welding
conditions proved great improvement between certain
plunge times and decreases there after.
• Nugget pull-out was the failure mode observed in
tensile tests.
References1. Rosendo T, Parra B, Tier M, et al. Mechanical and microstructural
investigation of friction spot welded AA6181-T4 aluminium alloy.
Mater Design 2011; 32:1094–1100.
2. Zhang Z, Yang X, Zhang J, et al. Effect of welding parameters on
microstructure and mechanical properties of friction stir spot welded
5052 aluminum alloy. Mater Design 2011; 32: 4461–4470.
3. Tozaki Y, Uematsu Y and Tokaji K. Effect of processing parameters
on static strength of dissimilar friction stir spot welds between
different aluminium alloys. Fatigue Fract Eng Mater Struct 2007; 30:
143–148.
4. Rosendo T, Tier M, Mazzaferro J, et al. Mechanical performance of
AA6181 refill friction spot welds under Lap shear tensile loading.
Fatigue Fract Eng Mater Struct 2015; 38: 1443–1455.
5. Lin Y-C and Chen J-N. Influence of process parameters on friction
stir spot welded aluminum joints by various threaded tools. J Mater
Process Technol 2015; 225: 347–356.