Laser welding Al–Si-coated PHS: equal line energy is not enough
Laser power and welding speed can produce different fusion-zone shapes, coating mixing and microstructures even when the nominal energy per unit length is similar.
The coating becomes part of the fusion zone
During laser welding of Al–Si-coated press-hardened steels, aluminium and silicon can enter the fusion zone. Their local concentration depends on coating dilution, liquid-metal flow and fusion-zone geometry. The result may be regions with different phase transformation behaviour and mechanical properties.
Research published in October 2026 evaluated laser power and welding speed separately. Power was the main factor controlling fusion-zone shape, while speed strongly influenced flow intensity, aluminium distribution and segregation. More homogeneous mixing was obtained with a characteristic Y-shaped fusion zone. A more continuous ferritic morphology was associated with poorer strength and ductility than a finer, dispersed morphology.
Why J/mm is not the full description
Line energy is a useful combined parameter, but it does not contain all information about beam–material interaction. Two power-and-speed combinations may have a similar ratio while producing a different keyhole, molten-pool flow and time available for coating mixing.
A WPS and process-development record should therefore retain power, speed, focal position, joint geometry and coating condition as separate information. A visually acceptable surface or similar weld width does not prove homogeneous fusion-zone chemistry.
Boundary of applicability
The results belong to a specific PHS, coating and experimental window. A Y-shaped fusion zone is not a universal acceptance criterion or an automatic target for every laser-welding application.
Source
- Rashkovets, M. et al.: Controlling coating dilution and microstructure through fusion zone morphology in laser welding of Al–Si-coated PHS steel, *Welding in the World*, 15 October 2026.
This is original technical commentary. No graphs, micrographs or tables from the authors have been reproduced.