As stated the galvanizing of the material has flowed into your weld causing porosity (voids) and the slag inclusion which causes the voids, simply put has the arc of your electrode burns through the galvanizing it flows into your welding puddle and disrupts it and actually acts as a flux wanting to cool your puddle and causes arc disruption allowing the flux from your 6013 rod to cool and cover your puddle prematurely. Again as stated grind the galvanizing off anytime you weld anything the cleaner the metal the more quality of a weld you will produce, arc welding is the most forgiving and a high penetrating rod like 6010 will burn thru dirty metal, rust, scaling and galvanizing, however it is runs "hot" and a more experienced welder is needed, often when welding out in the field on the jobsite we run a root pass of 6010 , which will burn the impurities out clean it, grind it if needed to help insure clean cover passes with 7018. I always employ a box fan when arc welding and blow the fumes off me.
More capacity of your power source will allow you to weld thicker metals, but again as pointed out previously grind your metal clean, if it's heavily galvanized you'll know you've hit base metal when sparks fly, grinding galvanizing just shoots dust till you hit base metal
As I read your latest reply, 70amps will not properly penetrate 3/4"
Edited by WrenchinOnIt, July 30, 2016 - 08:01 PM.