I built an intake plenum for a 4 cylinder engine. I used .090" h3003 aluminum sheet and 4043 filler rod. I put x creases in the panels to stiffen them. I used 1/8" pure tungsten and 1/16" filler rod. This is a turbocharged application and it sees quite a bit of pressure. After I fabricated it I built a pressure tester. cycling the pressure to 30 psi a couple of times results in cracks in the long seams. I initially drilled small holes at each end of the crack, ground the weld down to base material and re-welded. cycling after the repairs results in cracks in other areas. I have done a couple of plenums prior to this using heavier 6061 t4 plate and 4043 rod with no issues. Have I chosen the wrong base material or too thin? I am not a professional welder but I have some experience and from what I can see I have good penetration. I'm using a syncrowave 180. I am at the point of scrapping the assembly and starting over. I don't have a way to post pics at this point but really I would like to know about the base material and my choice of filler. Thanks.