The following post, Beginner Tips on Copper Alloys, was penned by Larry Peters, Project Manager, Building Materials of Copper Development Association as a response to many questions from fabricators via ListServe.
Thanks to the CDA, The National Ornamental and Miscellaneous Metals Association, and NOMMA’s Education Foundation (NEF) for the content. It provides excellent information on the selection, joining and welding techniques and chemical coatings for Architectural Bronze C38500 as well as other copper alloys. In our next two posts, we will cover beginner tips on copper alloys, first on choosing the right ones and then on fabricating and joining copper alloys.
How Do I Choose the Right Copper Alloy?
When purchasing or specifying copper alloys, always use an alloy’s unified numbering system (UNS) designation. (UNS designations begin with the letter C and are followed by 5 digits. See Fabricator’s Journal Vol. 19, October 2005 or visit: www.copper.org for more on UNS designations.) Never use just a colloquial name because those are not universally standard.
Educating your customers, contractors, architects, and designers on copper alloys, their various colors and their natural patination, may help avoid dissatisfaction regarding color based on expectation.
When color matching existing work, provide clients with alloy samples where a lacquered side illustrates non-aged color and a non-lacquered side illustrates how that alloy colors and ages over time.
Because it can be difficult and expensive to obtain some copper alloys in certain stock, like collar stock for example (particularly in small quantities), it might be cost effective to shape available stock with the use of a power hammer.
Because not every alloy is available in all stock shapes, there may be a need to fabricate a project using different copper alloys. If that is the case, you may choose to use whatever material comes in the shape you need or has the properties necessary to complete the work and then apply chemical patinas to get the entire project to match. But preplan first. It may be difficult to color match using chemical patinas too. Again educating your clients will them understand what is possible with certain alloys.
A good alloy to choose when customers request bronze is alloy C38500 (architectural bronze) because of availability of materials. However, C38500 should be annealed prior to forging.
Alloy C46400 or naval bronze also has good forge-ability and is available in rounds, squares, and rectangles. It typically works hot, like steel, and can be twisted, scrolled, tapered, and bent.
To compare structural properties of copper alloys to steel or other metals, request the minimum yield strength and tensile strength of the alloy in question from your suppler.
For sculpture work, a good copper alloy to use is C65500 or silicone bronze or pink bronze because it is easy to work with and discoloration is not detectable on welds after cleaning.
A good matching cast alloy for C65500 is C87300 or Everdur. It has good castability, weld-ability, and forge-ability. It can be gas and TIG welded with C65500 welding rod.
Copper Alloys Resources and Suppliers
A good information source when working with copper alloys is the Copper Development Association (CDA). You can even download the CDA’s booklet, Architectural Applications A4039, which discusses various alloys and available forms, and it has color photos of the alloys in various stages of aging.
Also view the NOMMA article, “Working with Bronze Cap Rail”
The Wagner Companies offers information on fabricating, welding, and finishing copper alloys.
Copper alloy suppliers (all are members of NOMMA):
Please share this post with others interested in copper alloys and read our next post on Copper Alloys Beginner Tips: Fabricating and Joining. We welcome you to share your tips on copper alloys in the box below!