The authoritative public forum
  for Metal Finishing since 1989
  

  -----

Is touch-up (Rust-oleum aerosol ) allowed per MIL-C-5541 class 3 gold?

We have a frame that is made from 6063 T52 aluminum tubing and weld-contructed using 5356 aluminum rod. The frame was designed in such a way that it an open end of a tube was welded to a closed end (the side) of another. This created huge air pockets and when we had it chem filmed per MIL-C-5541 class 3 (gold) our plater added some drain holes because acid got through pin holes in the welds and there was no way of getting the acid out. Obviously, or customer's drawing doesn't show these drain holes so we want to weld-fill them and then touch them up with a "Rust-oleum" metallic finish aerosol spray can. Our plater says that there is no way that he can plate them without using drain holes.

In the future, is there any product out there (such as Scotchweld) that once applied will hermetically seal welds and actually survive the chem film process...and actually get plated?

Martin Magaña
Quality Assurance Manager - Anaheim, California, USA
2007

---

Put on acid resistant rubber gloves ⇦ this on eBay or Amazon [affil links] , pick up a piece of cloth (not nylon), dip it in the chromate tank, swab the fresh filled holes until you get a yellow color. Or ,buy the "touch-up kits" from one of two most prominent suppliers of chromate processes.

Robert H Probert
Robert H Probert Technical Services

Garner, North Carolina

2007

---

2007
MIL-DTL-5541 [on DLA]F allows touch-up (using approved chem film per QPL-81706) of up to 5% of the surface if permitted by the customer.

Adding holes (or leaving weld gaps) to act as drains and vents requires customer approval, e.g., an ECO. Manipulate the part to fill & drain the cavity at each process step. Blow dry the interior after final rinsing. Negotiate the use of an epoxy or silicone sealant for the holes. Post-process welding is prohibited unless otherwise specified; heat damages the chem film. If plug welding is required, the entire heat affected zone should be touched-up as described by Mr. Probert.

There are many Scotch-WeldÐ products; some probably can resist the processing. I doubt that any qualify as an aluminum alloy or accept chem filming.

Alternatively, try improving the welding. Harris Products recommends Al 5183 as filler for Al 6063 although AloTec's chart shows 5183, 5356 & 5556 as equivalent. Al 4043 & 4643 fillers are better for crack-free welds although poorer for strength and ductility.

Ken Vlach [deceased]
- Goleta, California
Finishing.com honored Ken for his countless carefully researched responses. He passed away May 14, 2015.
Rest in peace, Ken. Thank you for your hard work which the finishing world, and we at finishing.com, continue to benefit from.