Other than hazardous health effects, what does zinc do to the integrity of a WELD when welding mild steel with 90/10 Ar/CO2 and .045 core wire? I haven't found a lot of info other than that of health hazards but I am under the impression that most zinc burns away when welding... maybe I should clarify that I am talking primarily of zinc coated/galvanized hot dipped steel.
Thanks in advance,
BJ
Short circuiting transfer can be used on galvanized sheet, but proper technique must be employed as you need to volatilize the galvanized coating ahead of the actual weld puddle. If you do not, you will have problems with porosity, cracking and spatter. It is generally easier to obtain consistant quality welds if you remove the galvanized coating prior to welding. This last statement is my personal opinion and the procedure I employ in my shop, the first part is published fact and can be reviewed in Lincoln Electric literature.
Mike Sherman
Shermans Welding
You really should remove the galv coatings before welding. The zinc gets sucked into the puddle and mixes with the weld metal and makes a mess. You should burn it off with a torch rather than grinding it away, as the zinc gets trapped in the grinding disk and redistibuted back into the joint, compromising the weld. Not everybody does it this way, and some Inspectors will let it go(galv brick shelf angle, pour stop, and such, I'm not talking critical joints like main members), but I don't like to chance it in our shop. It's easier to fix it before it gets to the field. Touch it up with cold galv. compound and you are good to go.
John Wright
A good place to find out more info on this is www.weldreality.com
there is a post site and info
The boiling point of zinc is 1180K while the melting point of steel is around 1800K. This means that as you weld over the Zn, it will volatilize. In general, this will lead to excessive weld spatter and porosity within your weld. - This has been mentioned by other respondents.
Another lesser known problem is that of liquid metal embrittlement. Here an area of the weldment that reaches just the right temperature can be attacked by the moulten zinc, leading to a brittle base material. (Especially in areas of high residual stresses.) Because the welding process leads to relatively short times at the elevated temperatures, this is not often a problem, but it is something to keep in the back of your mind.
Regards
Niekie Jooste
in addition to the above posts, i've welded on pieces of steel w/ heavy galv. coatings w/ gas shielded flux core and it seems like the zinc explodes underneath the weld after filler metal has been deposited, leaving a bigger crater to fill, and increasing the amount of heat input. sure is a pain in the butt when welding on 1/4" vertical up...had to switch to the stick welder to prevent burnthroughs.
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