F R A U N H O F E R - I N S T I T U T F R W E R K S T O F F - U N D S T R A H LT E C H N I K I W S

JOINING OF AL-CU MIXED COMBINATIONSTechnologies for Electromobility

info 300-4

Fraunhofer Institute for Material and

Beam Technology IWS

Winterbergstrae 28, 01277 Dresden,

Germany

Fax +49 351 83391-3210

www.iws.fraunhofer.de

Contact:

Dr.-Ing. Gunther Gbel

Phone +49 351 83391-3211

gunther.goebel@iws.fraunhofer.de

Motivation

Electromobility is what everyone is tal-king about nowadays. The Germanautomotive industry and its suppliersare adapting energetically to thesenovel developments. New companiesare being established in the field ofbattery manufacture, for example. The effective joining of aluminum withcopper is one of the central technicalchallenges involved in Electromobility.The Fraunhofer IWS Dresden has manyyears of experience in the joining ofdifficult-to-weld materials and ma-terial combinations which cannot befusion-welded by conventional means.It is, thus, in a position to be able tooffer various new joining technologiesto industry, which are able to performdifferent tasks and applications dealingwith the joining of aluminum and copper.

Process 1: Laser welding usinghighly dynamic beam deflection

The welding of combinations of variousmaterials enables optimum use of thespecific properties of those materials. Inparticular, laser beam welding is quitewell suited to the economic productionof mixed combinations. Nevertheless,the different thermophysical and mate-rial properties of the joining parts oftenlead to loss of quality, since any inter-metallic phases which are generatedcan greatly restrict the attainablestrength of the joint. The use of ahighly dynamic beam deflection at theFraunhofer IWS has shown that im-provements in quality can be attained with laser welding of the mixed com-binations Al-Cu.

1 2

With this technology, a brilliant laserbeam is deflected over quickly tiltablemirrors and projected on to the joiningimpact. The good focusability of high-brilliance laser beams makes it possibleto obtain extremely narrow weldingjoints with high aspect ratios andextremely short melt pool operatingcycles. The energy input into the work-piece is thereby considerably reducedand the formation of the brittle inter-metallic phases significantly decreased.

The results shown have been obtained within

the framework of the BMBF-sponsored project

WELDIMA Verfahrens- und systemtechnische

Entwicklungen zum Schweien von Mischver-

bindungen mit brillanten Laserstrahlquellen.

Process 2: FSW - Friction Stir Welding

FSW is a mechanical joining method,which combines the joining parts inthe solid phase. This makes it possibleto largely avoid undesirable metallurgi-cal fusion effects such as intermetallicphases from the very beginning. Therotating FSW tool exerts pressure onthe material surface at the joint via aso-called shoulder and plasticizesthe material by means of frictionalheat. A pin immersed into the mate-rial regulates the material flow. This makes it possible to obtain a fine-grain, thermo-mechanically treatedjoint seam with high strength values.

The process was realized at the IWS ona 3D milling processing center, whichis based on the concept of ParallelKinematics a so-called Pentapod. Thenecessary closed loop control strate-gies were implemented in cooperationwith the manufacturer Metrom GmbH.This machine concept permits both thethree-dimensional friction stir weldingof complex components and upstreammechanical processing of the jointedges in a clamp.

Benefits typical of FSW:- joining of materials which are diffi-

cult to weld using fusion weldingtechniques

- low component deformation

Comparison of the joiningprocesses

Process principle (schematic)

Characteristics

Applications

Friction Stir Welding (FSW)

- Solid-phase joining procedures

- For (three-dimensionally curved)linear joints, also with Al die casting,for example on casings

- Other materials: Al + Mg

Laser Welding using Beam Deflection

- Defined degree of dilution

- Thin-walled components - Example: contacting of Al-Cu

diverters for Li ion cells- Other materials: e. g. Al + Mg,

stainless steel + copper

500 m

Al

Al

Cu

1 Process of laser beam welding of

Al-Cu mixed combinations

2 Microsection of a laser-beam

welded Al-Cu combination

3 Pentapod equipment for friction stir

welding of Al-Cu

4 Laser induction roll plated and

twisted band of Al and Cu

3

Process 3: Laser Induction Roll Plating

Suitable composite semi-finished pro-ducts of aluminum and copper,adapted to the concrete componentrequirements, could open up new con-structive possibilities in the design ofelectrical drive components which areas compact and as light as possibleand nevertheless capable of bearinghigh mechanical loads. The LaserInduction Roll Plating procedure devel-oped at the Fraunhofer IWS is suitablefor the realization of such compositesemi-finished products. In this case, analuminum band and a copper band arecombined with each other in a singlerolling process and with low overall

deformation (< 11 %). The uniquenessof this procedure lies in the combina-tion of a conventional pre-thermaltreatment of both the bands to be joined and of a laser beam tapered toa line. This then heats the inner sidesof both bands to the temperaturesnecessary for the cladding processimmediately in front of the roll gap.This procedure is very suitable for themanufacture of e.g. bimetallic connec-tors (transition joints). The local influ-ence of deformation results in a com-paratively large degree of freedom inthe combination of the semi-finishedproducts to be joined. These do nothave to be geometrically congruentwith each other.

The results shown have been obtained within

the framework of the BMBF-sponsored project

DeLIZ - Produktionstechnisches Demonstra-

tionszentrum fr Lithium-Ionen-Zellen.

Laser Induction Roll Plating

- Joining by means of deformationand locally increased temperature

- Ribbon-shaped semi-finished pro-ducts, in planning: band on profile

- Example: joining of Al-Cu connectorsfor Li ion cells

- Other materials: steel + steel, Al + steel, Cu + steel

Electromagnetic Pulse Joining

- Atomic bonding, no thermal influence zone

- Particularly suitable for componentsalmost symmetrical in rotation

- Examples: piping, shafts, smallerpressure containers

- Other materials: z. B. Al + steel, Cu + steel, Al + Ti

- no additional welding material necessary

- manufacture of mixed combinationspossible

- high strength

Advantages arising from the newequipment concept:- equipment set-up which is much

simpler and far more cost-effective - large working area- high rigidity and position accuracy- quick and flexible process control

4

Process 4: Electromagnetic PulseJoining

By generating extreme local pressures,electromagnetic pulse joining permitsalmost fusion-free welding of practi-cally any metallic joining parts. Inter-metallic phases at the joint are therebygenerally avoided due to its inherentworking principle. Similarly, in the caseof mixed combinations, it is not criticalif the joining parts have greatly diffe-ring melting points, thicknesses orthermo-conductive properties. Thelocal pressure impulse is generated bymeans of the contact-free influence ofa magnetic field pulse in the compo-nent itself. Above all, this technologyoffers the possibility of a contact-freeforming of metals and of manufactu-ring positive-locking combinations in ahighly energy-efficient manner.

Atomic welding is also possible with acorresponding selection of the para-meters. This technology is particularlysuitable for piping or shaft compo-nents. Flat joint designs are howeveralso possible. One of the two joiningparts should not exceed a wall thick-ness of typically 2-4 mm. The weldingjoints display extremely low thermalinput and do not have any thermalinfluence zone. In addition to researchinto system technology, the IWS is also studying the optimization of joint quality by means of carefully adaptedtool coils and joining geometries.

This research was jointly sponsored by the Euro-

pean Fund for Regional Development and by the

State of Saxony.

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5 Microsection of an Al-Cu interface

generated using EMP

6 Piping pin mixed combinations of

Al-Cu

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2,0x10-4

6,0x10-4

8,0x10-4

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Electrical transition resistance of Al-Cu mixed combinations

Contacts at the Fraunhofer IWS

Laser Welding Dr.-Ing. Jens StandfuPhone +49 351 83391-3212jens.standfuss@iws.fraunhofer.de

Laser Induction Roll PlatingDipl.-Ing. Volker FuxPhone +49 351 83391-3243volker.fux@iws.fraunhofer.de

Friction Stir Welding &Electromagnetic Pulse JoiningDr.-Ing. Gunther GbelPhone +49 351 83391-3211gunther.goebel@iws.fraunhofer.de

500 m

Al

Cu