This document provides an overview of friction, explosive, and ultrasonic welding processes for aluminium. It describes the basic principles of each process, including how friction welding uses rotation and pressure to generate heat, explosive welding uses shock waves to join materials, and ultrasonic welding uses ultrasonic vibrations. It also discusses parameters for welding different material combinations like aluminium to steel. Diagrams show macrostructures and hardness curves for joined regions. The document aims to introduce these welding techniques and their applications for joining aluminium.

1. TALAT Lecture 4400
Friction, Explosive and Ultrasonic Welding Processes
of Aluminium
11 pages, 11 figures
Basic Level
prepared by Ulrich Krüger, Schweißtechnische Lehr- und Versuchsanstalt Berlin
Objectives:
− to give a brief introduction to friction, explosive and ultrasonic welding techniques of
aluminium
− to describe the possibilities and results of joining aluminium to different metals, e.g.
stainless steel
Prerequisites:
− General mechanical engineering background
− Basic knowledge in aluminium metallurgy
Date of Issue: 1994
 EAA - European Aluminium Association

2. 4400 Friction, Explosive, and Ultrasonic Welding
Processes of Aluminium
Table of Contents
4400 Friction, Explosive, and Ultrasonic Welding Processes of
Aluminium...................................................................................................................2
4400.01 Friction Welding ..................................................................................... 3
Principle of Friction Welding ..................................................................................3
Feasibility of Friction Welding Aluminium with other Materials ...........................4
Tensile Strength of Friction Welded Aluminium-Steel Joints.................................4
Hardness Curves in the Joint Region .......................................................................5
Preparation and Conduction of Friction Welding for an Al-Cr-Ni-Steel Joint........6
Friction Welding Parameters ...................................................................................7
4400.02 Explosive Welding..................................................................................... 7
Principle of Explosive Welding...............................................................................7
Macrostructure of Explosive Welded Joints ............................................................8
4400.03 Ultrasonic welding .................................................................................... 9
Principle of Ultrasonic Welding ..............................................................................9
Joint Forms with Ultrasonic Welding......................................................................9
Material Combinations for Ultrasonic Welding ....................................................10
4400.04 Literature................................................................................................... 11
4400.05 List of Figures............................................................................................ 11
TALAT 4400 2

3. 4400.01 Friction Welding
♦ Principle of friction welding
♦ Feasibility of friction welding aluminium with other materials
♦ Tensile strength of friction welded aluminium-steel joints
♦ Hardness curves in the joint region
♦ Preparation and conduction of friction welding for an Al-Cr-Ni-steel joint
♦ Friction welding parameters
Principle of Friction Welding
Friction welding is a process in which mainly rotationally symmetrical parts are rotated
while being pressed together, thereby generating heat of friction which causes the parts
to weld.
There are two main variations of this process:
− friction welding with a continuously applied drive
− friction welding using a flywheel drive
Characteristic for the continuous drive is an externally applied brake. The flywheel
drive, on the other hand, delivers its stored energy to the process thereby slowing down
itself. Consequently, this leads to differences in behaviour of the two methods regarding
torque and the compressive force being brought to bear (Figure 4400.01.01).
Principle of Friction Welding
with Continuous Drive with Flywheel Drive
1 2 5a 5b 1 5a 5b
4a 4b 6 3 4a 4b 6
Compressive Force Compressive Force
Based on Area 1 - Drive Based on Area
2 - Brake
RPM Torque
3 - Flywheel, Variable Mass
4a - Gripping Tool, Rotating RPM
4b - Gripping Tool, not Rotating
Torque 5a - Work-Piece, Rotating
5b - Work-Piece, not Rotating
6 - Working Cylinder
Axial Shortening Axial Shortening
Time Time
alu
Training in Aluminium Application Technologies
Principle of Friction Welding 4400.01.01
TALAT 4400 3

4. Feasibility of Friction Welding Aluminium with other Materials
The material data alone are not sufficient to indicate whether friction welding can be
successfully employed. Consequently, a number of alloys which cannot be welded by
other welding processes, can be welded effectively using friction welding. Parts to be
joined by the friction welding process, must have a sufficiently high strength to be able
to transmit the axial pressure and frictional moment as well as a sufficient hot forming
capacity.
Pure aluminium is ideally suited for friction welding. Out of the large number of
aluminium alloys and powder metallurgical materials available, there are still some
whose suitability for welding has still to be tested (Figure 4400.01.02).
Feasibility of Friction Welding Aluminium
with Other Materials
Steel, High Alloyed
Steel, Unalloyed
Steel, Austenitic
Steel, Alloyed
Al, Sintered
Magnesium
Aluminium
Zirconium
Mg Alloys
Ceramics
Zr Alloys
Al Alloys
Titanium
Copper
Bronze
Nickel
Brass
Aluminium
Al Alloys
Al, Sintered
Suitable for Friction Welding Partly Suitable for Friction Welding
Not Suitable for Friction Welding Not Tested
alu Feasibility of Friction Welding Aluminium 4400.01.02
Training in Aluminium Application Technologies with Other Materials
The following disadvantages limit the applicability of friction welding :
− The creation of low-melting phases or brittle intermetallic compounds.
− The softening of aged alloys.
− The amount and distribution of non-metallic inclusions.
− Hardening effects of the material combinations.
Tensile Strength of Friction Welded Aluminium-Steel Joints
Experiments with friction welding on different aluminium and steel alloys (for
parameters see Figure 4400.01.06) have shown that strengths exceeding the yield stress
of aluminium and steel can be attained. There is no straightforward correlation between
strength of alloys and strength of friction welded joints (Figure 4400.01.03)
TALAT 4400 4

5. Consequently, one can assume that other factors play an important role here. Such
composite joints exhibit brittle fractures with little plastic strain at the joining plane.
This is a result of the different mechanical properties of steel and aluminium. The
resulting inhibition of plastic deformation at the contact surface which occurs under the
influence of multi-axial state of stresses leads to the preferential building of cracks at
these sites.
Tensile Strength of Friction Welded
Aluminium-Steel Joints
400 1 - C 60
2 - St 37
2
N/mm 3 - 25 CrMo 4
4 - X 10 CrNiMoTi 18 10
300 5 - X 5CrNi 18 9
Tensile Strength
200
100
1 2 3 4 5 1 2 3 4 5 1 2 3 4 5 1 2 3 4 5 1 2 3 4 5
AlCuMg 2 AlMgSi 1 AlZn 4,5 Mg 1 AlMg 4,5 Mn Al 99,5
Source: Reiners, Kreye
alu Tensile Strength of Friction Welded
4400.01.03
Training in Aluminium Application Technologies Aluminium-Steel Joints
Hardness Curves in the Joint Region
The short welding times lead to correspondingly high hardness values. For aluminium
joints this is less of a problem than for composite joints of aluminium with steel. The
very narrow bonding plane, characteristic for the process, shows hardness peaks only in
a region of 100 to 200 µm (Figure 4400.01.04). Austenitic steels have a higher strain
hardening coefficient than ferritic steel and therefore reach higher hardness values. In
heat-treatable alloys the precipitates can go into solution, causing a softening of the
alloy. In heat-treatable alloys which respond to natural ageing, a precipitation of the
hardening particles occurs at room temperature, causing the hardness to rise again.
TALAT 4400 5

6. Hardness Curves in the Joint Region
400 x
x
300
Hardness HV 0,1 x
200 x
AlMgSi 1 x x x
x x x
x x
x x
x
X 10 CrNiMoTi 18 10
100 x
x x xx
x
0
8 6 4 2 0 2 4 6 8 mm
Distance from the Joining Zone
Source: Reiners, Kreye
alu
Hardness Curves in the Joint Region 4400.01.04
Training in Aluminium Application Technologies
Preparation and Conduction of Friction Welding for an Al-Cr-Ni-Steel Joint
The different thermal properties of the materials have to be taken into account while
preparing the welds. The surface area of materials with a low thermal conductivity
should be increased, in order to deliver a joining zone with good properties. In this
region, the grains are highly deformed (Figure 4400.01.05).
Preparation and Conduction of Friction Welding
for an Al - CrNi -Steel Joint
CrNi -Steel Al
before after
Friction Welding Friction Welding
Macrostructure of the Joint Zone
X 10 CrNiMoTi + AlCuMg2
0.05 mm
Preparation and Conduction of Friction Welding
alu
4400.01.05
Training in Aluminium Application Technologies for an Al - CrNi -Steel Joint
TALAT 4400 6

7. Friction Welding Parameters
Friction welding of aluminium with itself and its alloys as well as with steel is
characterised by extremely short welding times and high frictional and compressive
forces. As a result, the joining plane is kept extremely narrow, so that intermetallic
compounds and phases cannot be built. The diffusion zone characteristic for this region
is thus kept very small (< 1µm).
Friction Welding Parameters
Material Diameter Area-based Friction Compress- Circum-
(Massive) Friction- Compress- Time ion Time ferential
al Force ive Force
2 2
Speed
mm N/mm N/mm sec sec m/sec
Al 99,5 + Al 99,5 20 10 ... 30 30 ... 80 0,1 ... 4 2 ... 5 2,0 ... 4,0
AlMgSi0,5 + AlMgSi0,5 20 30 ... 80 50 .. 150 0,1 ... 6 2 ... 5 0,5 ... 2,0
Al 99,5 St 37
AlMg4,5Mn C 60
AlMgSi1 + 25 CrMo4 20 40 .. 70 65 .. 250 0,1 .. 1,1 3 ... 4 1,2 ... 2,3
AlZn4,5Mg X5CrNi18 9
AlCuMg2 X10CrNiMoTi18 10
alu
Friction Welding Parameters 4400.01.06
Training in Aluminium Application Technologies
Short friction times for aluminium are only relevant in connection with a rapidly
increasing force the friction and compressive phases (Figure 4400.01.06).
4400.02 Explosive Welding
♦ Principle of explosive welding
♦ Macrostructure of explosive welded joints
Principle of Explosive Welding
Shock waves (3,000 to 9,000 m/s) can produce pressures of up to 6 x 106 N/cm2. This
energy is utilised for explosive welding, especially for plates with large areas.
The shock waves spread out and create a "material wave" at the joining plane. At the
TALAT 4400 7

8. collision point a thin jet of material is heated to a high temperature, causing melting and
mechanical mixing at the interface (Figure 4400.02.01).
Aluminium can be effectively welded with itself and also with steel and copper giving
composite joints.
Principle of Explosive Welding
Detonation Front in Explosive
Expanding Products of
Detonation (Vapour) Unused Explosive
Sheet at Rest Explosive
Accelerating Joining Sheet
Plated Joining Sheet Joining Sheet
Air Shock Wave Air under Normal Pressure
Wavy Joining Zone Material Jet at High Velocity
Moving Shock Wave
Metal Interface Flowing Collision Point, Front in Air
Turbulent or Laminar Very High Stress
Base Metal
under the High Pressure (10,000 - 100,000 bar)
alu
Principle of Explosive Welding 4400.02.01
Training in Aluminium Application Technologies
Macrostructure of Explosive Welded Joints
The detonation force waves can be clearly seen as waves in a microsection. "Multiple
explosive welding" can be used to join a number of materials of different thicknesses
(Figure 4400.02.02). Even here it is possible to join materials which cannot be joined
by other processes.
Macrostructure of Explosive Welded Joints
AlMg2Mn0,3
Al Intermediate Layer
St 37
1 mm
AlMg4,5Mn
Al Intermediate Layer
Ni
X 3 CrNiMnMo 19 17
1 mm
alu
Macrostructure of Explosive Welded Joints 4400.02.02
Training in Aluminium Application Technologies
TALAT 4400 8

9. 4400.03 Ultrasonic welding
♦ Principle of ultrasonic welding
♦ Joint forms with ultrasonic welding
♦ Material combinations for ultrasonic welding
Principle of Ultrasonic Welding
In ultrasonic welding, frictional heat produced by the ultrasonic waves and force is used
for the joining process. Ultrasonic waves (15 to 60 kHz) are transferred to the material
under pressure with a sonometer. Welding times are lower than 3 s. The welding can
proceed with or without the application of external heat (Figure 4400.03.01).
Joint Forms with Ultrasonic Welding
The principle of the process limits the allowable mass of material on the sonotrode side
to a maximum of 10 g. The maximum thickness that can be welded, depends on the self-
damping characteristics of the work-piece material. A main advantage while welding
aluminium is the fact that the vibrations break the oxide layer and transport it to the
boundary regions. As a result, mechanical and chemical surface cleaning is not
necessary. Surface coatings (e.g. coated wire) and impurities behave in a similar
manner. Consequently, a main application area for ultrasonic welding is the contact
joining of wires (Figure 4400.03.02).
Principle of Ultrasonic Welding
F
F
Converter
Converter Vibrating Tool
Sonotrode Sonotrode
Vibrating Tool
Work-Piece
Work-Piece
Ultrasonic Vibration Ultrasonic Vibrations Support ( Anvil )
electrically heated
Weld Seam
US Roller Welding US Spot Welding
alu
Principle of Ultrasonic Welding 4400.03.01
Training in Aluminium Application Technologies
TALAT 4400 9

10. Joint Forms with US Welding
Two Parallel Wires
Two Wires with Bridging
Wire on Sheet
Wire Strand on Sheet
Sheet on Sheet
T-Profile on Sheet
T-Profile on Pipe
alu
Joint Forms with US Welding 4400.03.02
Training in Aluminium Application Technologies
Material Combinations for Ultrasonic Welding
Ultrasonic welding is particularly suitable for joining aluminium and its alloys with each
other as well as for producing composite joints with other materials (Figure
4400.03.03).
In electrical and electronic applications, the frictional energy creates clean welding
zones with low contact resistances.
Hardness influences the weldability of composite joints with steel. Hard alloys are less
suitable, since the plastic formability required for the joining is not sufficient. Very
often an intermediate layer is used to overcome this deficiency.
Material Combination for US Welding
Al Alloys with Al Alloys
Copper
Brass
Gold
Germanium
Steel, Iron
Mg Alloys
Mo Alloys
Ni Alloys
Pd Alloys
Pt Alloys
Si
Ag Alloys
Ta Alloys
Ti Alloys
Sn
alu
Material Combinations for US Welding 4400.03.03
Training in Aluminium Application Technologies
TALAT 4400 10

11. 4400.04 Literature
- Aluminium-Taschenbuch, 14. Auflage, 1984, Aluminium-Verlag, Düsseldorf
Neumann, A. und Schober, D.: Reibschweißen von Metallen. Fachbuchreihe
Schweißtechnik Bd. 107, Deutscher Verlag für Schweißtechnik 1990, Düsseldorf
4400.05 List of Figures
Figure No. Figure Title (Overhead)
4400.01.01 Principle of Friction Welding
4400.01.02 Feasibility of Friction Welding Aluminium with other Materials
4400.01.03 Tensile Strength of Friction Welded Aluminium-Steel Joints
4400.01.04 Hardness Curves in the Joint Region
4400.01.05 Preparation and Conduction of Friction Welding for an Al-CrNi-Steel
Joint
4400.01.06 Friction Welding Parameters
4400.02.01 Principle of Explosive Welding
4400.02.02 Macrostructure of Explosive Welded Joints
4400.03.01 Principle of Ultrasonic Welding
4400.03.02 Joint Forms with Ultrasonic Welding
4400.03.03 Material Combinations for Ultrasonic Welding
TALAT 4400 11