[FireKracker50]

I am making an aluminum tray out of .125" AL plate. I got it free so im not sure what it is but i assume 3003 or 6061.
It will be recessed into the floor of my boat and the trolling motor pedal will go inside it.
So far i have designed and cut all my pieces and tacked them together.

I am using 17 Torch with #10 gas lens because i needed the stickout in some places. 3/32" 2% lanthanated tungsten. 3/32" 4043. Seems like on other projects it has taken about 130 amps to weld this at full penetration. I found about 50Hz and a crayon point electrode worked best on other projects. When i was tacking this up i was using 120Hz and sharpened electrode to make more pinpoint tacks. But that was hard to do with 3/32" filler. I just didn't have anything smaller.

My first question is do i need to weld this all the way out on all sides or is a few 3" long stitches enough to hold it together. I don't want it to warp out of shape while welding. Also on the top plate only i don't want to disfigure it with full penetration bulging out the backside.

My second question is for this top lip i don't want the gap there for ascetics. i will be painting this in truck bed liner when completed and i want it to look nice.
Can i run around the lip without fill and it join together without cracking? Or will i need to add filler rod. I Dont want it built up around the edge and i would hate to have to weld around the entire perimeter then grind it all back down flat.

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[Bill Beauregard]

Yes, I'd weld all the way around. You likely want water tight. I prefer 4943 from Hobart Maxal. It melts at a slightly lower temp than aluminum base metal, and has more strength than 4043.

A copper bar clamped in the corner will benefit distortion. Keep welds as quick as you can, don't pile excessive filler in, and step around with a series of short welds

[FireKracker50]

So I started welding all the way around tonight doing about 3-4" at a time and skipping around. So far no distortion. I'll have to pick up some of that filler to try I've never used it before.
It doesn't need to be water tight. In fact I'm going to drill a whole and weld a piece of pipe on the bottom to attach a drain hose to that will route water into the bottom of the bilge area. But I don't think welding it all the way out is going to be a problem at all. Tonight's few minutes I worked on it went great.

So that brings me to my next question. The top lip, where it seems to the tray. It will be welded all the way around from the bottom side. But I don't want that gap on the top side I want it to look nice. After I weld the bottom. Can I close that gap by welding at low amps without filler? Or is that just asking for hot short cracking? The reason I'm wanting to weld without filler is because I don't want any build up.

Is there a good online retailer for just #1 of 4943. Most places I find u need to buy 10# and I will never use that much.

[cj737]

Filler or it will crack. You can also use 5356 and that is readily available over the counter most places.

[Bill Beauregard]

So I started welding all the way around tonight doing about 3-4" at a time and skipping around. So far no distortion. I'll have to pick up some of that filler to try I've never used it before.
It doesn't need to be water tight. In fact I'm going to drill a whole and weld a piece of pipe on the bottom to attach a drain hose to that will route water into the bottom of the bilge area. But I don't think welding it all the way out is going to be a problem at all. Tonight's few minutes I worked on it went great.

So that brings me to my next question. The top lip, where it seems to the tray. It will be welded all the way around from the bottom side. But I don't want that gap on the top side I want it to look nice. After I weld the bottom. Can I close that gap by welding at low amps without filler? Or is that just asking for hot short cracking? The reason I'm wanting to weld without filler is because I don't want any build up.

Is there a good online retailer for just #1 of 4943. Most places I find u need to buy 10# and I will never use that much.

A point I believe is fact, but I've never heard an expert state, so it is my belief not fact:
Aluminum is very weak when it freezes. If it cools too slowly, it shrinks while still in the weak state. Each dip, or if you use lay wire draws heat out of the very hot weld before it can crack. It also adds thickness to reinforce. I've tried it. I can watch the crack form when no filler is used.

[FireKracker50]

Yes i understand the hot short cracking fairly well.
And i always use filler. My only question was this joint specifically.
If you think about it like this...
In essence you have an inside corner joint with a 1/32" Gap welded with 4043 filler. My question is if i weld the outside corner joint at very low amperage without filler metal added will it crack. Im just looking to seal the seam for aesthetics. Being that there is a small gap and its welded on the other side with filler i was hopeful that it would pull a little bit of the filler into the weld and the fact that i was using very low amperage would minimize heat input.

If you all still think it will be prone to cracking i will just weld it up with filler and then grind it all down flat.

[Bill Beauregard]

Moving faster, with more amps is the road to low heat input, outrun the conduction of heat. It is my belief that not using filler allows more time in transition between freeze, and strength.

Add 1 LB of 32 degree water to a pitcher of 70 degree water. it cools it 38 BTU. Add 1LB of 32 degree ice to the same pitcher the cooling effect is 784 BTU. A BTU is defined as the effective heat to raise the temperature of 1 lb of 70 degree water 1 degree F.

Filler has a similar effect to ice. dip filler into a puddle, the heat consumed by changing aluminum from solid to liquid causes the back of the puddle to freeze. Meanwhile the Heat Affected Zone both sides of the seam is expanding, and cooling very rapidly, shrinking. Tension against soft aluminum causes cracking.

Generous preheat might save you. Everything shrinks together without the tension.