A clean weld is a good weld

What’s wrong with this weld?  That’s the question I am asked frequently via email or on welding forums. Usually the first thing I do is scan the picture for tell-tale signs of at least some attempt at cleaning the metal.  Usually that is the culprit, at least in part.  Whether it’s steel or aluminum, precleaning  a weld is extremely important.  TIG welding is the process that is most sensitive to cleaning.   TIG is usually a clean process, yielding nice, clean welds that need little or no post weld cleaning.   But if the metal is not clean, it will show up very quickly. The welds will look brown, sooty, dull or even spattered.  The tungsten or cup may look contaminated and dirty as well.  If the metal is clean, you should end up with a nearly gleaming weld, on either steel or aluminum.   Take time to grind the metal for steel, and brush it for aluminum.  Then wipe it down with a safe cleaner like aluminum cleaner or acetone.  Do not use brake cleaner or other chlorinated solvents.  Using a flap disk on steel can work if it is fresh and new, but what typically happens (and usually where the issue is when customer tell me they cleaned the metal) is that the disk is worn, and all it ends up doing is polishing the mill scale to a nice shine.  The same issues can be found in MIG and stick welds, though and usually will result in some sort of porosity.