Aluminium can be welded to steel for ships and offshore structures by incorporating explosively bonded transition joints
Triplate is made of three layers – LRA ship plate grade A steel, pure aluminium and corrosion resistant aluminium alloy 5083, which contains 4.5% magnesium, less than 1% manganese and a trace of chromium. These are explosive bonded together in a vacuum by Dutch company Shockwave Metalworking Technologies.
Welding methods are similar to those for the parent metals, with the proviso that the temperature of the aluminium-steel interface must not be allowed to exceed 315ºC. Using a heat-sensitive paint can monitor this.
Ideally, the aluminium weld should be made first, after the removal of the aluminium oxide film by wire brushing, followed by de-greasing. Argon shielding gas is recommended. The steel weld is made using a coated electrode.
Shear strength between base metal and interlayer is greater than 55 N/mm2, while through thickness strength is greater than 75 N/mm2. Standard Triplate strips, available in the UK from Aalco Metals, are 3.8m long, 24mm wide and 34 to 35mm thick. 16mm and 32mm widths are also available and lengths up to 5.8m can be made to order. The joints meet the requirements of all relevant international standards, including MIL-J-24445A.
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