Triplate transition joints The ultimate solution to weld aluminium to steel By Ko Buijs Metallurgical engineer SMT-Metals b.v.

Production route of Triplate Choice of right materials and study of features Choice of right materials and study of features Grinding of the surfaces Grinding of the surfaces Preparing of special grade explosives Preparing of special grade explosives Preparing vacuum chamber Preparing vacuum chamber Explosion welding Explosion welding Flattening of the plates Flattening of the plates Cutting into bars and special shapes Cutting into bars and special shapes Inspection by QA-manager and independent surveyor Inspection by QA-manager and independent surveyor Transport to customer Transport to customer After sales and all kind of recommendations After sales and all kind of recommendations

What happens during welding? Steel plate Aluminium plate Explosives S = collision point  high pressure will locally cause super plastic behavior of metals

Metallic bond between Al and Fe

Applications in the marine sector Cruise vessels and mega yachts Cruise vessels and mega yachts Offshore platforms Offshore platforms Fishing vessels Fishing vessels Ferries Ferries Tenders and supply boats Tenders and supply boats Special ships such as navy vessels Special ships such as navy vessels

Some examples

Differences with open air cladding Triplate is manufactured in a vacuum environment Triplate is manufactured in a vacuum environment Therefore we need less explosives Therefore we need less explosives This will lead to a smooth interface This will lead to a smooth interface The result is no oxide conglomerations in the interface The result is no oxide conglomerations in the interface Better bending properties Better bending properties Less risk of corrosion Less risk of corrosion Easy to machine Easy to machine

Three different interfaces

Open air cladding versus vacuum Source: Oxide conglomerations are visible Small holes will initiate corrosion in due course especially when bend Disadvantage during bending and cutting Limited fatigue strength

Atmospheric cladded transition joints

Side bend test Vacuum clad generates no oxide holes

Hammer bend test MIL-J-24445A Oxide holes can initiate cracks after bending Combination hammer bend and side bend test

The result of crevices

The strength of the interface Even at bending radius 2x width Triplate shows no cracks. Tensile test

Summary of differences Open air cladding Open air cladding Oxides with porosity Oxides with porosity Oxides initiate fractures Oxides initiate fractures Holes initiate corrosion Holes initiate corrosion Side bend radius 10x width of the strip Side bend radius 10x width of the strip Variable weather conditions Variable weather conditions Harder to machine (sawing and bending) Harder to machine (sawing and bending) Vacuum cladding Vacuum cladding 100% dense 100% dense Does not apply Does not apply Side bend radius 5x width or even less Side bend radius 5x width or even less Does not apply since it is inside Does not apply since it is inside Easy sawing and forming thanks to high ductility Easy sawing and forming thanks to high ductility

The right set-up of Triplate

Transit zone shear strength in N/mm 2 Relationship between temperature and shear strength aluminium/steel transition joints after 200 hours heat input.

Temperature gradient during welding Subjected to normal circumstances. It’s relevant to first weld the aluminium plate to the transition joint

Unacceptable configurations The interface will overheat during welding. That will cause an hard brittle interlayer.

What happens when the temperature is too high during processing of Triplate? Brittle aluminium iron crystals 760Hv Aluminium 99,5% 23Hv Steel 127Hv

Tensile test asymmetric set-up Triplate is not the weakest link in the chain

Special shapes by means of water cutting Full freedom of design and digitally controlled

Triplate butt welds Butt welds are labour intensive Butt welds are labour intensive Butt welds are expensive Butt welds are expensive Difficult to seal it in a right way Difficult to seal it in a right way Avoid butt welds as much as possible Avoid butt welds as much as possible Therefore longer lengths available (5.8 m) Therefore longer lengths available (5.8 m)

Various approvals such as Lloyd’s, Veritas, RINA, Germanische Lloyd, Det Norske Veritas and American Bureau of Shipping

Many thanks for your attention