Welding Annealed Aluminum

Date 04-11-2012 12:56

I'm welding some brackets and bosses to a tube. The brackets are .190" thick (5052-H32 material), the bosses are a 1" solid rod with a 1/4" hole (6061-T6), and the tube is 4.00" x 0.065" (6061-T6). The welding process is GTAW, with 5356 filler material, and 100% argon. The welds are fillets.

Our benders had the tubes annealed from the T-6 condition into the T-0 condition, to avoid breaking the tubes, with their bending process. We had the tubes annealed into the T-6 condition after bending. The tubes are leaking near the bracket welds during pressure testing.

6061-T6 and 5052-H32 are fairly clean materials. The 6061-T6 material changes into a dull gray / black after annealing it from T-6 into T-0, and back into T-6. We clean with acetone, dry, and wire-brush prior to welding. We also preheat to 150* F.

Question: What am I missing?

Should I preform the same annealing changes to the brackets and bosses?

Would it matter if I change from T-6 into T-O, and back?

Any help would be welcomed.

Keith

By Lawrence (*****)

Date 04-11-2012 13:43

Keith

Honestly... I've never heard of a heat treatable aluminum alloy going from T-6 to Zero, and then back to T-6 I diddn't know that was possible, even if you had used heat treatable filler metal.

You say the leaks are coming "near" the bracket welds... Does this mean that mean that the leak is NOT in the weld and totally in the base metal?

150 degree F preheat does nothing to help or hinder in your scenero

I wish I could be more helpful... Your problem is super interesting :)

By Ke1thk

Date 04-11-2012 14:51

Lawrence,

Tube bending is a gray area. The part is 18" long and has a 90* bend, forming an elbow. T-6 is a hard condition, while T-0 is soft.

Our CNC benders have much power. So much so, that they'll deform the tube, including ripping it in half, to unacceptable defects. The T-6 condition is very hard to bend. The force is similar to a tensile test. We have the tubes annealed to T-0 to allow for bending. The print requires the T-6 condition. So...we buy with T-6, change it to T-0, and change it back to T-6.

The heat treatments of the tube are prior to welding. Yes, it looks as though the leak is within the tube itself, and not the weld. The bubbles are a fine mist. The weld looks fine, considering the tube is a filthy gray / black condition.

Keith

By DaveBoyer (*****)

Date 04-12-2012 02:03

Are You bending the tubes after welding or before?

If bending after welding, try bending a few before welding, and have them pressure tested. This will prove if the tube is ductile enough to withstand the bend.

A pressure test performed with the parts welded to an unbent tube would determine if the bending had anything to do with it.

A pressure test of unwelded, unbent tube will prove if the tube is pressure tight as delivered. Try before and after annealing.

By Ke1thk

Date 04-12-2012 12:34

We're bending before welding. The tube won't fit into the bender if we weld all the brackets and bosses on first. We're going try to pressure test after bending and annealing, but before welding, to see if the tubes leak as a result of bending.

By 99205

Date 04-12-2012 00:41

Is the wire brush leaving score marks on the metal?

By Ke1thk

Date 04-12-2012 12:39

Yes, but the deeper marks are from the bender clamping marks.

By leonan Date 04-20-2012 15:00

the chemical composition of 6061 is risky in terms of hot cracking. If you weld 6061 autogeously it will crack easily. However, the likelihood of cracking can be reduced by adding the right filler wire - either 4043 or 5356. The filler wire must be added with enough volume to change the chemical composition of the weld. Besides, if too much heat input is reduced during 6061 welding, the base metal that close to the weld (fusion zone) will be partially melt, and accordingly micro cracking is formed during solidification. So you might want to do PT right after you finish the weld to make sure there is no micro cracking on the fusion zone.