Aluminum TIG Welding Help

I had several small cracks on welds in an oil pan..on the baffles
As you can see in the photos - the weld cracks when it cools....I know this is a sloppy looking weld (3rd attempt after grinding out the bead and re-welding)
On the first 2 attempts the entire weld cracked (about 1.5" length) when it was cooling (pulled) so on the last attempt I spread the outer flanges with a 3/8 bolt and coupling nut (long) and then released the tension as it cooled....and only cracked about 1/2"
I'm using 4043 3/32" filler rod...
Any ideas? I realize this crack will not effect the pan function but would like to fix it anyway.

 

I would use 5356 filler rod little more ductile. An use a little per heat too help the puddle get started. Weld around the corner as much as you can too filling the crater at the end.

 

Thanks for the tip! I will get some 5356 rod and make it look pretty this time too!
The weld has to be fairly flat at the corner as there is a windage tray that lays in the corner with 4 Dzus buttons...but I guess I could trim the corner of the windage tray just a little...

 

While I'm at it....maybe a little larger cup for aluminum? Seems like this was a #6 cup....could it use a little more shielding to keep the edges of the weld cleaner?

 

Problem with welding aluminum that's had oil on it is the oil will wick into the crack and then wick out when the heat of the weld hits it. (dirty weld)Usually a little pre heat from a small propane torch will help move the oil out of the joint, wipe it away. then use a good aluminum cleaner.

 

Protex Aluminum cleaner can help and be sure you have enough Argon flow.