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Published on Apr 7, 2014
The Copper Development Association is pleased to present a series of video presentations covering the welding of copper-nickel alloys. In this segment, we will cover the preparation steps for welding these alloys, as well as some of their properties.
We're presenting the information in "welders language" for the benefit of those doing the actual welding. However, this information should also be of help to the engineers, design personal and others who work with the alloys indirectly.
These videos have been produced on site in a large fabrication facility, and we ask your understanding for the environmental background noise.
Before a weld arc is struck, here are some basics on copper-nickel alloys and important preparations for welding.
The two main grades of copper-nickel alloys used in industry are 90-10 (90% Cu and 10% Ni) and 70-30 (70% Cu and 30% Ni). In metallurgy these are described as SOLID SOLUTION ALLOYS. This means any amount of copper is completely soluble in nickel and any amount of nickel is soluble in copper.
So why is this important in joining copper-nickel alloys? As you may know in welding materials like a low alloy steel, it may be necessary to use a pre-heat or post-weld heat treatment or both to prevent weld cracking and maintain good properties. This is due to alloy phase formations which have different structures than the base metal, making weld and heat affected zone hard, brittle and possibly prone to cracks.
No such phase develops in copper-nickel alloys as result of welding. Of course this also means the alloys can not be strengthened by a heat treatment. The alloys can be strengthened only by cold working. However the copper-nickel alloys are very ductile so it takes a considerable amount of cold working to bring about a significant amount of strengthening.
There are elements that in even small amounts are very detrimental to copper-nickel alloys, and if present on the surface before welding, they can cause embrittlement and cracking in the weld or heat affected zone. The elements that are particularly harmful are lead, sulfur, phosphorus and other low melting point metals. Reputable copper-nickel mills follow international guidelines to keep these elements at very low levels. They have to... otherwise they would not be able to hot roll the alloys. . Cleaning of the surfaces next to the weld joint prior to welding is essential. These stray elements may come from sources like oil, grease, cutting lubricants, marking crayons, paints, or just plain shop dirt.
Typical cracking that may result from failure to remove these elements is shown here. This illustration is actually pure nickel welded with a sulfur residue on the surface.
The weld area should be cleaned to remove oil, grease or other contaminant prior to welding. This can be done by first removing excess contaminant by wiping with a clean cloth, followed by wiping with an approved solvent. The organization using the solvent should assure that the solvent is not harmful to personnel.
In addition to this video presentation there is also free printed literature covering all aspects of fabrication, welding, corrosion resistance and other subjects of help to all involved with the alloys. We invite you to visit www.coppernickel.org or contact firstname.lastname@example.org to access this literature.