Originally Posted by
everlastsupport
Nice work Jake and great presentation as well.
Looks like a quick job since you didn't have to degrease it and no pre-heat. That keeps the time down.
What electrode did you run? Using 5356 it probably is a lot stronger too.
I use lanthanated (1.5% or 2%) tungsten electrode for almost everything. It starts easily, has no potential radioactivity safety risks, and holds a point well, allowing concentrated arc heat. In this case it would be 3/32" most likely. (Sharpened like a pencil, and then rounded just a little bit at the tip, for increased current capacity.)
I'm always looking for the "happy medium" of what I can get away with to get a part adequately prepared for acceptable weld quality, without "breaking the bank" on spending an excessive amount of time.
On this one, it looks like I used primarily my carbide burr, but I am sure I also spot-cleaned it afterward with some solvent as well. In fact I remember some of that yellow paint dissolving and peeling. The paint was really weakly adhered and not very chemical resistant (wouldn't surprise me if it was DIY spray can applied?)
The carbide burr is about the only tool I have that could vee out a crack like this in a fillet / tight spot (reaching deep into the the "gullet" of the casting, for example.) If chatter marks are acceptable, it can also be very quick and effective for removing a dirty oxidized surface and expose fresh, sometimes immediately "ready to weld" aluminum. You do have to be careful when using it however, and hold it securely. Or it can take off sideways on you! 
Originally Posted by
jdt1986
Very nice what did you do to prep the joint? And why did you use 5356 im only curious i know 5356 offers alot more strength but i thought 4043 would be a little more towards this application.but it still looks excellent no porosity it must have been a hair line fracture . Thats pretty weird that the other side didnt break or crack usually cast aluminum doesnt give at all
Aluminum could crack like this IMO, by fatigue. Many repetitive "back and forth" cycles of even moderate force (even safely below the original peak tensile failure strength of the material), could eventually degrade the mechanical qualities of the material, until the point of failure. An improvement is to increase the rigidity of the structure somehow, such as by changing the shape (thickening a beam chord size, width, etc,) to decrease the stress loading of the material. Even a modest increase in beam thickness, like say 20%, can reduce the material tensile loading by a huge amount. A lower peak material tensile loading will allow the part to endure many, many more cycles before fatigue failure. At least, that is how my mental model of fatigue failure in aluminum works. Perhaps John ("sportbike" on here) will chime in with additional info, as he is really the expert on aluminum metallurgy and modes of failure I believe.
No "high strength alloy" aluminum part is completely immune from fatigue related failure by the way. It's just a matter of time (and how many cycles) before any aluminum part will eventually "give it up". (or so I've heard.)
Originally Posted by
everlastsupport
Not to speak for Jake,
On this piece, 4043 would probably (most likely) have worked as well. 4043 is an easier to use silicone based filler and a lot of aluminum casts are silicone as well (because it's easier for the parts to release when they're made). 4043 is not quite as as strong. With the location of this bracket it will not see any real high temps so 5356 was the better choice (IMHO) based on strength. 4043 handles higher temps better, but the location and use of the part 5356 was a good choice.
Or, after all that rambling, maybe Jake had no 4043 filler?
Mike's assessment is in line with my views and experiences. You select the filler rod based on a bunch of different factors, (and it can be complicated, especially when you are guessing what the parent alloys are, as we usually must do when performing aluminum welding repairs.) The alcotec filler rod selection chart is a good resource for at least understanding about different pros/cons of different aluminum filler rod selection for different applications:
http://www.alcotec.com/us/en/support...on_Chart-2.pdf
I usually have ample supplies of 4043 and 5356 (and some other rarely used alloy fillers), however sometimes if I have a half-burned stick of some filler rod, I will try and find an excuse to melt it, instead of grabbing a fresh stick of something. 
There is actually a touch of (acceptable, minor) porosity in the area where I didn't prep the surface as well. "weathered" dirty, wet, painted, etc oxidized aluminum surface can have all kinds of contaminants in it that basically bottom line, have hydrogen in it. Hydrogen = nice and happy in the molten aluminum puddle, but causes hydrogen gas bubbles (porosity) upon puddle solidification. It's always a good thing to try to avoid. If you do find yourself welding on a contaminated surface however, the best thing you can do is run a "low amp" arc over it and try and not melt very deep at all. The goal is the get the contaminants (often, hydrocarbons for example) up to a "vaporizing or burning" temperature to convert them into vapor that will offgas. If you attempting welding with hydrocarbon like contamination in the area, excess hydrogen can be dissolved into the molten aluminum welding puddle, which will then upon puddle solodification become trapped as hydrogen bubbles, potentially buried very deep down inside the weld bead, (aka ""porosity") resulting in a brittle, low strength weld deposit.
Last edited by jakeru; 06-18-2011 at 09:01 PM.
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