we are welding a aluminum rail 1/2" plate and 3/4" round bar both 6061 t6 material and 4043 filler metal plug weld condition , using GTAW ,we are cleaning with a cleaning solution for aluminum weld mark WM 781, inspection is visual and PT ,visual is ok but when we PT we get some indication at the TOE of the weld and heat effected zone that we cannot explain does anyone know what this could be and explain it to us i will try and post photos
Thank you all any help you can offer
I read in one of the articles of Mr Frank Armao that it is difficult to liquid penetrant test aluminum. The aluminum oxide on the surface is porous. If you are not careful about cleaning off the penetrant before spraying the developer, you will get all sorts of spurious penetrant indications. The cracks we see probably are confined to the area next to weld that has been cleaned by arc. These cracks are also very very shallow, only 0.002 to 0.003 inch deep. You can check by sanding them lightly and then liquid penetrant test again. If cracks go away they were very shallow.
These cracks are caused by adjusting the high frequency intensity too high. Many people make a mistake of setting the HF intensity to maximum and leaving it there. In most cases it causes no problem because HF is on only briefly at the arc start. However, in aluminum AC welding, the HF is on continuously. If it is set too high, it can etch the surface of aluminum adjacent the weld. Beacsue grain boundaries in aluminum are areas of higher energy, the HF etches them preferentially. So the cracks are preferentially etched grain boundary network. The etching is very shallow but deep enough to hold dye penetrant.
The remedy?
Turn the HF intensity down a bit and cracks will go away.
Just a point Waqasmalik, I think you misunderstood something Frank Armao said.
The High Frequency (HF) used for GTAW of aluminum and DC GTAW arc starting is very high voltage and very low current and is "superimposed" over the welding current.
Superimposed HF cannot and never has caused material defects on aluminum or steel base metals....
All "etching" comes from the DC+ (reverse polarity) side of the AC cycle.... Another term for the etching is cathodic cleaning or cathodic bombardment.
The high frequency for AC acts to stabilize the arc and eliminate "rectification." Rectification is when the welding current passes the zero point on the sine wave and the arc extinguishes but does not ignite on the other half of the cycle, causing a sputtering and poor AC welding arc... The superimposed HF, causes a clean ionized path for the welding current to easily make the jump from the end of the tungsten electrode to the work and visa versa.
The "intensity" of the HF can cause problems with other electronic equipment in the vicinity of the welding operations (interference) so it is typically recommended that the lowest intensity setting that will make a good weld is what you select.
The micro fissures you are describing are caused by other things.
I looked
contamination imho
could be many things
first the filler
anything on the hands or gloves that touches the filler
bad bottle of gas
so many, just 2 off the top of my head
btw try 4049 maxal filler omg another cheap plug
got to stop doing that
sincerely,
Kent
Dye penetrant can bleed and bleed and bleed.
The pictures do not reveal a "defect" as far as I can see. (but that first pic is really easy to magnify)
You have not provided us any of your acceptance/inspection criteria or described the problem beside "some indication at the toe"
I suggest a second inspection, vigorous clean/wipe with cleaner prior to applying developer..
Apply developer much more lightly, just a dusting, and be ready with a 10 power magnifying glass.
I suspect you have one or two pores that are holding dye and just bleeding all over the place...
Do you want to reduce porosity? of course... But does the cause of all that red mess necessarily qualify as a rejectable defect? How could we possibly know..
Say more about your the standard you are inspecting to.
We are inspecting to D1.2
Thank you all for the help
Have you looked at the toe of the weld under 10X magnification?
I would agree with Al,
I have been doing PT on aluminum regularly for a little over 2 years now and we see this often. It is usually when the edges of the weld become depleted or eroded and get nearly a "dry lake bed" texture. PT bleeds in it no problem and make for e messy indication. Usually when we have a lot of welds like this to do we have the customer prep the welded areas with a very light sanding, of maybe an orbital or a stainless wire brush and it gets it off 99% of the time.
Try doing aluminum with level 3 fluorescent penetrant, bring a sleeping bag when you're there with DCMA.
J
All I have to add is an emphasis on cleanliness before and during welding. If you look at the base metal in the area of the toe in that photo, what some folks call the PMZ, or partially-melted zone, it will look like dry lake bed; a series of cracks that are, as Lawrence and Al pointed out, very shallow to begin with. This condition is not caused by any one thing, but in my experience you can almost completely eliminate it by adopting two habits: clean, clean, clean (base metal, filler, gas), and adjust your amperage for the thicker member, not the thinner. Aluminum loves to absorb heat quickly, but sheds it quickly as well. If you're welding a thin piece to a thick piece, and you adjust your amperage low to avoid a meltdown, your thicker piece will have the described condition. Somewhere on here I once posted a photo of this very problem (although without the pretty red dye pen). :) Just one last thing: the stainless steel wire brush must be CLEAN. Get a bunch of them. Good luck.
Some in the aerospace sector refer to the problem as arc erosion. The penetrant indications you are seeing are shallow in most cases and can be removed by a vigorous wire brushing operation. Do not use a power brush, simply wire brush the weld and adjacent surfaces with a hand brush. Use a stainless steel brush.
I always wire brush the weld and the adjacent surfaces with a stiff stainless steel wire brush before attempting to perform the penetrant test. This approach usually eliminates the problem entirely.
If after wire brushing the joint, followed by the penetrant test, there are penetrant indications, repeat the wire brushing operation and reapply the developer. The latter, the bleed back technique, will determine if the indication needs to be removed by more aggressive means. If the welding standard prohibits the bleed back technique, repeat the penetrant test in its entirety once the initial penetrant indications are removed.
Aluminum is soft and can be smeared easily. Discontinuities such as porosity can be concealed by power brushing, sanding, or grinding operations used to clean or finish the weld. Lightly tapping the finished surface with a stiff stainless steel brush will often reveal the porosity as a slight indentation. I usually "pop" the indentation with a sharpened tungsten or scribe.
To reiterate:
1) fit the joint,
2) wire brush the joint, brushing in one direction using a hand brush, pushing the stainless steel brush toward the free edge,
3) weld the joint,
4) wire brush the weld and adjacent surfaces, again using a hand brush with stainless steel bristles,
5) perform the penetrant test,
6) wire brush the surfaces containing penetrant indications in the areas adjacent to the weld,
7) reapply the developer (repeat the entire PT if the bleed back technique is prohibited by the welding standard),
8) if penetrant indications reappear after vigorous wire brushing, a more aggressive removal technique is required.
Good luck - Al
And DO NOT USE the stainless wire brush or any other implement if it already has been used on carbon steel or some other metal... Separate areas in your shop to make sure the Aluminium doesn't become contaminated from grinding carbon steel as an example or any other potential source of contamination... Don't fabricate the different metals on the same table or lay the down on top of each other... Excellent explanations to this problem from all who participated... 
