Welding Defect in Brass

Have you put it under an SEM and done an Auger/XRF analysis for clues as to what is causing the porosity? is there carbon residue in the pores? If so it could be bad cleaning practices and/or workpiece porosity.

I'm going to take a wild guess (seeing as how all I have is a photo to go by) that the workpieces have not been properly cleaned and you have a contaminant embedded in surface porosity of the workpieces that is being instantaneously vaporized by the laser. Possibly some solvent residue perhaps? This is my strong gut reaction.

Are the workpieces cast? wrought? sintered? How are they cleaned? How are they dried after cleaning? Is this a new phenomenon that has just cropped up in an existing process or is this a new process that has never made good welds?

If it is an existing process that has just started trowing you bad welds, then you need to look VERY closely at what has changed recently because something did. New solvent supplier? new raw material supplier? new welder settings? new guy on the job doing something different from the older guy?

It is an existing process that has just start our bad welds. But we did not change anything such as material supplier, welder setting, guys.

The workpiece was wrought. But after laser welding, it has been induction heating to brazing with copper tubes and cleaning by weak acid.

We think it was caused by raw material, could you please give me some advice for how to check that? Analysis which elements? Zn? Pb? or impurites?
THanks again!

Again, the first step is to put it in an SEM and find out what elements are in the porosity by XRF/Auger analysis and then the next step is to figure out where the element(s) is/are coming from. Until you find out what elements you have in the pores, everything else will be guesswork.

SOMETHING changed. Don't convince yourself that nothing changed because SOMETHING had to change. It might be something that nobody in a million years would have thought had anything to do with it. Were the workpieces stored after cleaning and possibly contaminated in the interim? did something change at one of your vendor's operations that you don't know about? Did THEY change their processes? Is a different mill making your raw stock? do you have access to an older sample of the product (say an engineering prototype or weld coupon) to compare chemistry of the workpieces against?

Are the welds performed under a protective atmosphere? (argon, CO2, helium etc.) If so, could the gas have been contaminated? or do you have a pinhole leak in a regulator diaphragm or a loose fitting that is sucking atmospheric air into the system? or a plugged up nozzle that is not spraying the gas properly or at the right spot?

As you see, there are a lot of possible variables and until you figure out what is in the pores, you are spinning your wheels.