Welding

1. Friction Stir Processing and Friction Surfacing –
A Review
Presented by
C.S. Ramachandran,
Doctoral Research Scholar (Full Time),
Centre for Materials Joining & Research (CEMAJOR),
Department of Manufacturing Engineering,
Annamalai University
Annamalai Nagar

2. Friction Stir Processing (FSP)
FSW has a number of attributes that can be used to
develop a generic tool for microstructural modification
and manufacturing.
FSP was developed based on basic concept of FSW.
FSP has led to several applications for Microstructural
modification in metallic materials like
Superplasticity, microstructural refinement of
cast Al alloys, homogenization of nanophase Al
alloys and MMCs, SMMCs, SMMNCs etc.,

3. Superplasticity
Two basic requirements are necessary for superplasticity.
The first is a fine grain size, typically less than 15
microns.
The second is thermal stability of the fine microstructure
at high temperatures.
Advantage of this process is that it can form large and
complex work pieces in one operation. The finished
product has excellent precision and a fine surface finish.

4. SP formed parts does not suffer from spring back or
residual stresses. Products can be made larger to
eliminate assemblies or reduce weight, which is critical
in aerospace applications.
Conventionally, thermo-mechanical processing (TMP)
is used to produce fine-grained microstructure in
commercial aluminum alloys.
A typical TMP for heat-treatable Al alloys consists of
solution treatment, overaging, multiple pass warm rolling
(200–220 Deg C) with intermittent re-heating, and a
recrystallization treatment.

5. Clearly, TMP is complex and time-consuming and
results in increased material cost.
Conventional superplastic strain rate of 1 X 10-4 to 1 X
10-3 S-1 obtained in TMP adopted for automotive
components is too slow.
For mass production oriented industries, there is a
need to develop new processing techniques with high-
strain rate (>10-2 S-1).

6.  FSW/FSP results in generation of 0.1– 18 microns in
various Al alloys.
 The grain size range in the FSW/FSP aluminum alloys
is within the grain size range required for attaining
structural super plasticity.
 The effectiveness of FSP for processing fine-grained
materials that are amenable to HSRSPF. Second, the
microstructural refinement in FSP aluminum alloys can
be controlled by adjusting the FSP parameters

7. Mishra et al., MSE(R), 2003
 2024 Al: abnormal grain growth at high temperatures
 Al–4Mg–1Zr: effective pinning of grain growth by fine Cr-
bearing dispersoids and MgZn2-type precipitates, and
Al3Zr dispersoids, respectively

8. It is important to understand the effect of alloy chemistry,
FSP parameters on the thermal stability of fine
microstructure of FSP Al alloys.

9. Production Surface composites using FSP
 MMCs reinforced with ceramic phases exhibit high
strength, high elastic modulus, improved resistance to
wear, creep and fatigue, which make them promising
structural materials for aerospace and automobile
industries.
 MMCs suffer from a great loss in ductility and
toughness due to incorporation of non deformable
ceramic reinforcements, which limits their applications
to a certain extent.

10. For many applications, the useful life of components
often depends on their surface properties such as wear
resistance.
Hence, it is desirable that only the surface layer of
components is reinforced by ceramic phases while the
bulk of components retain the original composition and
structure with higher toughness.
In liquid phase high temp. processing (casting), it is hard
to avoid the interfacial reaction between reinforcement
and metal matrix and formation of some detrimental
phases.

11. A target depth of 2.03 mm resulted in incorporation of SiC
particles into Al matrix with 1.8 mm pin, 25.4 mm/min,
300 rpm (a). However the bonding of surface composite
layer and substrate plate was influenced by the traverse
speed. At 101.6 mm/min (b) traverse the surface
composite layer was separated from Al alloy substrate

12. Tool shoulder geometries for SMMCs (Copyright 2001,
TWI Ltd) (after Thomas et al).

13. Microstructure of as-cast and FSP A356 (standard
threaded pin, 900 rpm and 203 mm/min)
FSP eliminated the porosity, FSPed A356 experienced
intense stirring and mixing, resulting in breakup of the
coarse acicular Si particles and dendrite structure and
homogeneous distribution of the Si particles throughout the
Al matrix.
FSP of Cast Al Alloys

14. A crack in A356 Al cast alloy successfully
repaired using friction stir processing

15. Joining of Metal matrix composites
 Weldability of these MMCs is significantly reduced due
to the addition of ceramic reinforcements.
 The drawbacks associated with the fusion welding
include: (a) the incomplete mixing of the parent and filler
materials, (b) the presence of porosity as big as 100
microns in the fusion zone, and (c) the formation of
undesirable deleterious phases such as Al4C3
(embrittlement).
 A solid state welding technique is highly desirable for
joining the metal matrix composites.

16. Optical micrographs showing SiC particle distribution in
(a) base metal and (b) the weld nugget in 7093Al–15
vol.% SiCp composite.

17.  A critical problem associated with FSW of MMCs is severe
wear on the FSW tool due to the presence of hard
ceramic reinforcements.
 The wear rate of the tool increases linearly with increasing
linear welding distance (Nelson et al., Met. Trans., 2001)
 High-temperature wear resistance would reduce damage
to the tool.
 Furthermore, the design of tool geometry is also important
to reduce the tool wear. Active heating of composite work
piece before welding may also contribute to reducing tool
wear due to improved flow properties of composites at
high temperature.

18. Comparison between room-temperature tensile
properties of FSW, TIG, and base 6061Al–B4C
composites (after Nelson et al).

19. Friction Surfacing
Friction Surfacing is a process where a coating material, in
rod form is rotated under pressure, generating a
plasticised layer in the rod at the interface with the
substrate. By moving a substrate across the face of the
rotating rod a plasticised layer between 0.2-2.5mm thick is
deposited.

20. During Fiction Surfacing, the applied layer of metal
reaches a temp. near the melting point whilst
simultaneously undergoing plastic deformation.

21. Inherent benefits of the Friction Surfacing process:
 Excellent metallurgical bonding with no inclusions,
porosity or oxidation
 Dense, clean & fine microstructures
 Non-weldable (super) alloys can be deposited
 No melting of materials, Negligible dilution
 Small localised HAZ, No cracking in the HAZ
 Automatic & highly repeatable process
 Similar or dissimilar materials can be bonded

22. Khalid Rafi et al., 2010, the effect of traverse speed
on coating characteristics of friction surfacing of
stainless steel type 310 on low carbon steel.
Low carbon steels: widely used for structural
applications, moderate strength and ease in fabrication
LCS: poor corrosion resistance at normal atmosphere is
a matter of serious concern.
Fusion welding: suffers from dilution, Thermal spray:
mechanical bonding and Friction surfacing: negligible
dilution and good metallurgical bonding.

23. Coating Material: AISI 310 grade stainless steel (in wt%:
0.1 C, 24.77 Cr, 19.51 Ni, 1.29 Mn, 0.47 Si, and balance
Fe) used as the coating material was taken in rod form
with 100 mm length and 18 mm diameter.
Substrate: AISI 1020 grade low carbon steel (in wt%:
0.12 C, 0.42 Mn, 0.02 P, 0.01 S, and balance Fe) which
was used as the substrate, had dimensions of 100 mm X
150 mm.
Parameters: The axial force was kept constant at 10kN,
constant at 800 RPM and traverse speed was varied
between 1.2 mm/s and 5.6 mm/s.

24. Microstructure of AISI 310 base metal
mainly used for high temperature corrosion applications.
regarded as difficult to weld as it is prone to solidification
cracking

25. Typical coating produced by friction surfacing
ripples

26. width similar
to the dia. of
the rod
staggered
edges on
retreating
side &
reduction
in effective
width

27. thinnest
coating
discontinuou
s distribution
of plasticized
metal
thickest
coating

28. Prolonged plastic deformation
time, formation of large
volumes of plasticized metal.
Insufficient forging effect,
poor consolidation, lack of
bonding locations at the
interface
Thinner coatings, efficient distribution of plasticized metal,
clear coating-substrate interface without any unjoined
regions.

29. Optical micrograph
at the interface
SEM- secondary electron
image at the interface
The interface corresponding to higher traverse speed
shows well bonded coatings with good bond integrity

30. OM of coating shows fine
equi-axed 2-8 micrometer
grains due to dynamic
recrystalization.
Higher strain rates and
higher temp. due to severe
plastic deformation leads
to rapid softening and
plasticization of near
interface regions in
consumable rod and
subsequent deposition of
plasticized metal on the
substrate.
SPD will be more
pronounced in the
consumable due to size
constraints and limited
heat dissipation.

31. thinner coatings,
intimate adherence,
high bond strength,
Thicker coatings, very poor bond
strength, insufficient consolidation of
plasticized metal

32. The U bend test results were taken into consideration
as an evidence for good bond integrity.
Minor cracks
Crack free

33. The combined effect
of heat and plastic
deformation causes
a decrease in the
grain size which
leads to hardening
at the regions close
to interface.
Shear band formation

34. MMC coating on Al Si alloy, G. M. Reddy, J. Surf.
Engg., 2009

35. Optical microstructure of AA 2124
SiCp MMC over A356 Al–Si alloy
The MMC consumable was in
the form of rod of 15 mm dia.
The rotary speed was 1800
rpm, 3mm/ min, 5kN load

36. XRD of composite coating produced by friction surfacing
process
The absence of Al4C3 indicated that there no melting
during surfacing operation

37. High hardness is due to high volume fraction (25%) of the
hard SiCp which are uniformly distributed in Al MMC
coatings

38. The pin 4 mm dia. and 30 mm length. The counterpart discs
were made of hardened alloy steel with surface hardness of
65 HRC. The applied load was 0. 5 kg and sliding speed
was kept constant at 640 rpm. The total sliding distance for
the test was 6 km.
POD
Test

40. Worn surfaces of A356 and A356 T6
are very rough with numerous
adhesive craters and deep
ploughing grooves due to severe
adhesive wear
The hard particles have high
resistance to the micro cutting
process of the moving disc. Hence
very smooth glazed surface was
produced; the wear loss of this
specimen is very low.

41. Summary
Researchers all over the world now recognize the
benefits of using solid-state welding processes for
additive manufacturing.
For example, friction stir processing friction welding
processes are under active consideration for additive
manufacturing.
Use of friction surfacing for additive manufacturing,
however, is an all-together new idea. While many
other countries are making rapid strides in additive
manufacturing, work in this area is to begin in a
systematic manner in India.

42. Thank you

43. Springback Definition: Condition that
occurs when a flat-rolled metal or alloy is
cold-worked; upon release of the forming
force, the material has a tendency to
partially return to its original shape
because of the elastic recovery of the
material. This is called Springback and
influenced not only by the tensile and yield
strengths, but also by thickness, bend
radius and bend angle.
A356 alloy in T6 condition solution
treatment at 530 Deg C for 1 h
and aged at 140 Deg C for 8 h)