Aluminium voor Scheepsbouw

Aluminium voor Scheepsbouw

Aluminum Shipbuilding Alloy Development
Project duration: ~ 18 months

Background
An aluminum plate mill orders a new alloy at their R&D. The alloy has to be developed within 2 years, including approval from the major ship classification bureaus. Even after welding the new alloy shall be 20 % stronger then AA 5083, which was the standard ship building alloy, and the corrosion resistance shall be comparable to AA 5083.
Only a very tight budget is available.

The Project
In the project team, Hans van Veen was as metallurgist / welding engineer one of the five engineers and responsible for welding and approval by Det Nork Veritas.
Experimenting was started with 15 alloys, based on literature study and good guesses. These alloys are cast and rolled on laboratory scale, 1.6 mm gauge instead of 8 mm. Welding tests and corrosion test were carried out.
Based on the results of the laboratory alloys, 6 alloys are cast and rolled on full scale. On the full scale material welding and corrosion tests are repeated. The two most promising alloys however show something like “knife line attack” in the heat affected zone after the corrosion test on welded material. This is unacceptable and the project faced a dead end.
The solution was found using a high alloyed aluminum welding wire, after thorough study of the phase diagrams. This wire adds a surplus of one of the major alloying elements in the heat affected zone by diffusion during welding. This approach was a success, no attack was found. With slight change in alloy composition the knife line attack was solved.

Result
The alloy is now known as “Alustar” (AA5059). Its strength, even in the welds, is about 20 % higher, its weldability and the corrosion resistance are excellent.