Treatment for Brass Laser Welding Joint

Brass + ammonia = big no-no. Why would anyone try to do this?

Thanks for your comments! But our current product is brass welding and it must meet the requirment of UL: after 10days ammonia test, there is no crack observed by magnify. Am I right that it is impossible to pass the test if we welded the brass by laser welding? Heatreatment and painting is no hleping for this?

I misunderstood your context, and was thinking more of long-term exposure.

But wouldn't painting the joint defeat the purpose of the test?

I am curious as to the application. Brass is not one of the readily welded materials for the Laser process. I assume the weld is autogenous and there may be the reason you are experiencing cracks. Are you bound to the laser process by specification or code? There are probablly better weld processes available should you have the option.

What specificlly is the application for the weldment?

We choose laser weld brass because of it's low heat input. There is a seal gasket near the welding joint and the gasket will be failed if the temperature higher than 200 degree. So we choose laser welding.

Low heat input is a good reason to select laser welding, but why not use projection welding at about 1/10 the cost and similar heat input?

It's a good idea. But our parts is pre-assembly by threads, and the two parts could not have relative motion in the welding process. The pre-assemlby is to assure one specification for our parts, so I think it is not a proper method for our parts. All our competers weld this joint by TIG or plasma. The joint is stronger than ours.

Attack of brass by ammonia will be more rapid in locations under tensile stress which could be your fusion or HAZ. Those locations should be protected from ammonia.

Caution! You must consider the severity involved in the use of your part. Before ammonia test, does the part already present crack under 25X magnification? If so, the part should be rejected. If not, it would be dangerous hide welded region with a layer of paint to try pass it in the test, because when in use, this layer might come loose and having residual stresses or micro-cracks, this brass in presence of ammoniacal environments and mechanical tensions can easily suffer stress corrosion cracking.

It would be better if you relieve the stress by heat treatment (170 ºC / 10 h).