Triplate Transition Joint

A transition joint that is homogeneously bonded together by vacuum-explosion welding and is often used in shipbuilding for welding an aluminium superstructure to a steel hull.

Triplate® consists of three metals with a steel base material, a corrosion resistant aluminium alloy as the upper layer and, to promote bonding, pure aluminium as the intermediate layer.

The explosive cladding/welding process produces a perfect metallurgical bond which is stronger, more secure and more durable than traditional rivets & welding. Due to its superior bend radii and flexibility more complex profiles can be produced with Triplate®.

Size & Range

Dimension	Value
Standard strip width	Variable
Standard strip length	max 3800mm
Standard strip thickness - steel	15 or 18mm
Standard strip thickness - aluminium	12 or 16mm
Standard strip thickness - total	27 or 34mm

Range

Size (mm)	Comments
3800 x 16 x 34	Triplate meets MIL-J-24445A and is approved by Lloyd’s Register of Shipping.
3800 x 20 x 34	3.1 certification supplied unless requested otherwise.
3800 x 25 x 34	3.2 Lloyds available upon request at time of production.
3800 x 30 x 27

Whilst similar products are manufactured by explosive welding in atmospheric conditions, the unique shockwave process produces superior results as shown below.

Atmospheric vs Vacuum Cladding

Atmospheric	Vaccum
Coarse oxide agglomerations with porosity at the steel aluminium interface.	100% dense, homogenous joint.
Oxide agglomerations & porosity initiate fracture.	Does not apply.
Oxide agglomerations & porosity can cause corrosion, in spite of protective coatings.	Does not apply.
Bending of aluminium-steel strips can be difficult due to the coarser bond structure.	Very good formability due to ductile aluminium-steel joint.
Production control is limited by variable weather conditions.	Optimal process control due to constantly reproducible vacuum conditions.
Aluminium-steel joint is hard, making sawing & forming difficult.	Easy sawing & forming due to ductile aluminium-steel joint.

Properties

Mechanical Properties

Property	Value
Shear strength – Basemetal/Intelayer	>55N/mm²
Tensile strength (through thickness)	75N/mm²
Processing temperature	max 315^oC
Bend test base material in compression	Acceptable
Bend test base material in tension	Acceptable
Side Bend Test	Acceptable

Chemical Composition

Layer	Material
Base material	Steel LRS Ship-Plate Grade A or St 52-/3N
Interlayer	99.5% pure aluminium - Alloy 1050A
Superlayer	Aluminium alloy 5083 (AlMg4.5Mn)

Processing

During processing the temperature of the material MUST NOT be allowed to exceed 315°C.
DO NOT pre-heat the transition joint before welding.
Welding methods to be used are similar to those for the parent metals.
Ideally the aluminium weld should be made first after removal of the aluminium oxide film by wire-brushing, followed by de-greasing. Argon shielding gas is recommended. Small diameter wires are recommended (1.2mm). Welding methods include GTAW, GMAW, TIG, MIG and Synergic pulse MIG.
The steel weld is made using a coated electrode and GMAW, SMAW or FCAW. Small diameter electrodes are recommended (2.5mm).
When bending ensure that the minimum bend radius is at least ten times the strip width or thickness.