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Joining of dissimilar materials
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motivation
During the last years a reinforced usage of lightweight construction and mixing of materials could be observed in transport facilities. Causes of this development are on the one hand the demand for fuel saving on the basis of weight reduction and, on the other hand, reasons of environment protection by saving of issues CO2.
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Difficulties whilst joining steel and aluminium
The welding of steel with aluminium is a hybrid process. While the aluminium is fused, the melting temperature of steel is not being reached. This is called a weld brazing.
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The difficulties when welding steel and aluminium are on one hand the different physical characteristics like melting temperatures, electrical conductivities, thermal conductivities, densities, thermal expansions as well as, on the other hand, the appearance of friable intermetallic phases with mainly rather difficultly constructed space lattices with limited possibilities of transfer movements. Therefore they are hardly capable of distortion.
The morphology of the intermetallic phases is determined by different factors which influence themselves mutually and depend on each other:
- Proportion of alloying elements steel:aluminum
- Distortion state of steel
- time-temperature-run at the join patch
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To achieve welding connections with high firmness, following procedures are possible:
- careful selection of the chemical composition regarding the basic materials by bringing in the alloy elements which constrict the phase area
- accurate selection of the filler material
- Application of coatings onto a steel - or aluminum sheet
- exact control of the temperature in the fusion zone
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Welding process for joining steel and aluminum
For the connection of steel and aluminum, special welding procedures are required.
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The "DeltaSpot‘Process"
With the DeltaSpot process a new resistance spot welding procedure was developed. It stands out due to high stability and reproducibility of the deliverables. This is accomplished by using a process known band, which is conducted around the electrodes, protects them against pollution and guarantees a higher efficiency due to lower power comsumption.
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The "CMT" process
The abbreviation "CMT" stands for "cold metal transfer", referring to an innovative gas shielded arc welding process with a few special features.
-> also go to CMT-Cold Metal Transfer
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"TWIN" welding
Bimetal strip Twin welding
A bimetal strip of steel and aluminium is welded on each side with the similar material. Doing so, a connection of steel and aluminium can be produced, which, put into practice, can satisfy many demands. Laser beam welding is carried out at the same time.
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