Q: We need to join a …-in. piece of copper to a 1-in. piece of steel. We prefer to use gas metal arc welding, and would like to know the correct filler metal, and shielding gas to use.

A: A common filler metal that can be used for this application is aluminum bronze, ECuAl-A2.

This alloy commonly is available in 0.045 in. and 0.0625-in. diameters, and you could use either 100 percent argon or a 75 percent argon – 25 percent helium mixture. Higher helium blends or pure helium can be used, but will prove to be more costly.

Preheat and minimum interpass temperature must be 1,000 degree F.

Selection of wire diameter between 0.045 and 0.0625 in. will be determined by the current capacity of your welding equipment.

Q: How do I perform a penetration/soundness test on an aluminum fillet weld that has a 1-in. base plate and a 0.500-in. vertical plate?

A: A good reference can be found in AWS D1.2 Structural Welding Code - Aluminum, Section 3 Qualification, 3.10 Soundness Tests – Fillet Welds.

In this section, under Option 1, there is a good, general explanation with a reference drawing (3.17) and acceptance criteria on how to perform a soundness test.

The thicknesses of the members you listed call for a weld size of 0.500 in.

The test calls for a 12-in. minimum weld length, and sample plates that have 6 in. minimum width.

Two, 4-in.-long samples are removed from the center of the test coupon for a break test, and a sample is removed from each end of the test plate for a macro specimen.

The break samples are loaded, to cause the unwelded side to open, and placing the root of the fillet tension.

If the sample breaks, the fracture surface should be inspected for root penetration and porosity along the fracture surface.

Acceptance criteria are given in the code. The macro section specimens should have the cut surface smoothed and etched to expose the weld area. While there are many good solutions that you can use to etch the aluminum to perform a macro examination, I have used sodium hydroxide (NaOH) mixed with water, and found that quite effective.

A common mix would be 90 grams of NaOH to 90 ml of water. In a pinch, you may consider standard oven cleaner found in the grocery store to etch the samples as well.

Q: We are welding 304 stainless steel tanks with a 308L welding wire and have noticed the following characteristics:

1. A magnet will grab a little bit at the weld joints after welding.
2. A magnet will stick to the 308L stainless weld wire.

Can you help us to understand why this happens?

A: There are two factors involved in your observations.

First the 308 weld metal normally is designed to contain a small amount of ferrite in the austenitic matrix to prevent hot cracking. Ferrite is ferro-magnetic.

That explains why the magnet is slightly attracted to the weld metal.

The welding wire situation is different because there is no ferrite in the wire after the rod stock from which it was produced is annealed. Annealing causes all of the ferrite in the wire to transform to austenite, which is not ferro-magnetic.

However, the wire is cold worked during drawing, and the cold working causes transformation of some of the austenite into martensite. Martensite is ferro-magnetic.

Melting the wire eliminates the martensite, so the weld metal contains no martensite unless you cold work it.

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.