My latest welding experiment was some 1mm stainless steel strips to some 5mm mild steel square bar. Joining thick and thin has previously caused me problems when welding with MIG and I’m not sure how it copes with mixed materials. The advantage here for TIG is it’s ability to mix metals and the control over the arc which makes it suitable for thinner materials.
I filed off all of the millscale from the 5mm bar, this was not needed on the stainless. When fitting up, I clampped some heavy duty bar on top of the thin sheets to take away some of the heat. The arc was struck on the 5mm bar and then the puddle was washed over the thinner strip to avoid it burning away too much. No filler was used except for a couple where I’d burnt back the metal. I used a 1.6mm tungsten and the current setting was 60A.
I believe that the reddish colour on some of the welds is a problem but I’ve not had any feedback yet.