Q: Can 2024 aluminum be welded to 6061 aluminum?

A: 2024 aluminum is limited in its weldability, was intended for mechanical fastening and is considered unweldable.

This alloy will be very prone to liquation cracking in the partially melted region of the heat-affected zone (HAZ).

The 6061 aluminum also is somewhat prone to liquation cracking in the heat-affected zone as well, but not as sensitive as 2024.

Keep in mind that in attempting to weld these materials there will be a loss of strength primarily in the heat-affected zone for different reasons:

In the 2024 material, precipitates will go back into solution, and that will result in a large drop in strength.

In the 6061, the material will over-age and will drop to the low to mid 20 ksi range for strength.

There is not much information on the drop in strength in the heat-affected zone of the 2024, primarily because it is considered unweldable, but you could expect it to drop off in the range of 40 percent to 50 percent.

Q: We weld 1½ in. black steel pipe into handrails.

We grind the weld joints smooth, then sand them smoother, then send them to be hot dip galvanized.

When the handrails come back from the galvanizer, there is a build up of zinc at all of the welds that makes the joints look as if they were never ground or sanded.

We are using e70 s6 wire. Is there another wire that will not attract the zinc in the galvanizing tank?

A: The main issue with galvanizing is the silicon content of the materials being coated.

The greater the silicon content, the greater the rate of buildup of coating thickness.

The steel you are welding likely was manufactured in accordance with ASTM A53 and contains little to no silicon.

The ER70S-6 gas metal arc welding wire can have 0.80 percent to 1.15 percent silicon, and that can yield a deposit silicon content of in the range of 0.60 percent to 0.95 percent, depending on shielding gas.

The differential in silicon content of materials will yield a build up differential of 2 times to 5 times the thickness on the weld metal compared to the black steel pipe.

Keep in mind that silicon is a necessary component in the composition of gas metal arc welding wire. Without the silicon in the wire, the weld would have full porosity.

So, you may consider changing from an ER70S-6 an ER70S-3 gas metal arc welding consumable.

The ER70S-3 gas metal arc welding wire has a specified range of silicon from 0.45 percent to 0.75 percent. It is one of the lowest silicon gas metal arc welding consumables.

The silicon in the weld deposit will be in the range of 0.30 percent to 0.55 percent, and, again, that depends on the shielding gas used that would reduce the build-up of the galvanizing material. However, you still will find that the buildup may be excessive even with this change.

To achieve a major reduction in the build up of the galvanizing, the deposit composition of silicon should be less than 0.30 percent, with the best results coming with contents below 0.15 percent.

The filler metals that can achieve such low deposit silicon contents are limited.

For your application the most likely usable filler metal would be a low slag version of Lincoln Electric's E6011, Fleetweld 35LS that has a silicon deposit content of 0.10 percent.

The American Galvanizers Association has a good document that describes the root cause of your problem and makes good filler metal suggestions. That document is available on line at www.galvanizeit.org/images/uploads/publicationPDFs/T_WHDG_02.pdf.

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This column is sponsored by Penton and the Lincoln Electric Co., Cleveland. Dave Barton is a senior welding engineer in the Application Engineering Group of The Lincoln Electric Co. He oversees welding procedure development for both new technology and existing products, performs failure analyses for customers, and serves as a consultant on welding application problems. Barton has been with Lincoln Electric for 21 years. Send your questions for Mr. Barton in care of WDF by e-mail to: askdav@penton.com.

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