plating, anodizing, & finishing Q&As since 1989
Corrosion After Laser Marking on 17-4 Stainless Steel
August 19, 2010
After passivation and laser marking of 17-4, corrosion shows up on the laser marked areas only, during salt fog testing. Secondary passivation does not alleviate the issue.
Has anyone had this issue, and perhaps found a strategy to avoid the corrosion.
Validation Consultant - Middle Haddam, Connecticut, USA
August 27, 2010
Laser marks on stainless are a very common problem because the process is disturbing the surface in a way that encourages corrosion.
The problem with secondary passivation processes is that oftentimes the laser mark fades before the usual full acid bath immersion time is achieved. Most people simply pull the parts from the bath just short of the point where fading begins, but clearly this is making a compromise between a visible mark and corrosion resistance. The fact that the mark is composed of material the passivation bath wants to remove means that the mark is composed of material that will want to rust (i.e. free iron).
Occasionally I have seen parts where the laser marker has hit the sweet spot of a mark that remains unchanged despite a long dip in passivation acid. If you can get there at all, that's your best bet.
Stellar Solutions, Inc.