Elastic Modulus of Copper at Brazing Temperatures

Date 12-10-2014 21:00

Ferrari,

WELCOME TO THE AWS WELDING FORUM!!

I am not an engineer nor a metallurgist. BUT, you have me curious with your temps and application.

Are you talking 1050°C? or °F?

I thought I remembered lower temps so I looked it up. Copper melts at about the temp you sited, 1980°F approx or 1085°C approx. And you are right there.

Commonly used brazing temps for copper are much lower, usually closer to 1000°F and not generally above 1500°F. Not disputing that your usage can't be done, just not common. Is this a pretty massive part? Not asking for details incase it is sensitive information.

Is the quality of the joint the important factor or are you actually trying to anneal the end product? The annealing obviously makes it weaker/softer and in some cases that would not be beneficial.

Enough with my questions. Hopefully one of our brazing experienced members will be along with more help.

He Is In Control, Have a Great Day, Brent

By FerrariEngineer Date 12-10-2014 21:14

Hi Brent-

Yes the assembly is brazed at 1030°C using a 35/65 Au/Cu alloy; so you are right, the tempertautre is just below the melting point of Cu. So you can imagine the copper is real soft, that is why I'm thinking the E must be much lower that posted values for general "annealed" Cu....

The qulaity of the joint is not a factor, we are concerned about the material defelcting under vacuum, so I am running an FEA model. We are limited in realestate so instead of using a higher E value and having a large FOS, I really need to know a more accurate value for the material as-is removed from the furnace.

The one disadvantage of brazing Cu at high temperatures is the annealing behavior, which is typical for hydrogen brazing.

Thx

By welderbrent (*****)

Date 12-10-2014 21:30

Okay, thanks for the information. I'm always interested in what others are doing. Hopefully that will assist some of our wiser and Brazing competent members in providing you an answer that will actually get you somewhere.

Brent

By ssbn727 (*****)

Date 12-11-2014 18:53 Edited 12-11-2014 19:51

Here you go Ferrari engineer,

Do you have this toolbox?

http://www.engineeringtoolbox.com/young-modulus-d_773.html

http://www.engineeringtoolbox.com/young-modulus-d_417.html

Here's another portal that can be helpful:

http://www.copper.education/kd/10.cfm##

Here's another tool to have when working with Cu:

http://www.copper.org/resources/properties/703_5/

http://www.copper.org/publications/pub_list/soldering.html

And this for quick reference:

http://www.howany.com/how-to-calculate-modulus-of-elasticity/

Oh, I almost forgot:

http://www.thefabricator.com/article/arcwelding/brazing-copper-and-copper-alloys

http://www.lucasmilhaupt.com/en-US/brazingfundamentals/properbrazingprocedure/

http://www.copper.org/applications/plumbing/techcorner/soldering_brazing_explained.html

http://www.thefabricator.com/article/tubepipefabrication/brazing-copper-tubing

http://www.brazing.com/techguide/procedures/copper_welding.asp

http://www.altairusa.com/brazing-copper.php

http://www.copper-brazing.net/images/copper-brazing.pdf

These folks can offer you some really good advice... In fact, all of the above can also offer some excellent recommendations:

http://www.htg.cc/

http://www.cuprobraze.com/over_tech.asp

EDIT: This is from the SAE: "Automotive Metallurgical Joining
1970-10-01
Standard
J836_197010
It is generally intended to reflect current usage in the automotive industry; however, it does include some of the more recently developed processes. More comprehensive coverage of materials, processing details, and equipment required may be found in the Welding Handbook, Soldering Manual, and other publications of the American Welding Society for Testing and Materials. ...More comprehensive coverage of materials, processing details, and equipment required may be found in the Welding Handbook, Soldering Manual, and other publications of the American Welding Society for Testing and Materials. AWS Automotive Welding Committee publications on Recommended Practices are particularly recommended for the design or product engineer." I'm going to take a look in my own AWS Welding handbooks to see what is relevant to your application and if you could attach an image of something similar it would be most helpful for any of us to assist you further...

You wrote: "35/65 Au/Cu alloy" is this correct? 35% Gold? and the rest Copper? if true, that must be an expensive part! Since I cannot see what it is you're engineering, I can only offer some links to references and contacts that may be able to help you better... In any event, I hope you can find what you're looking for. :grin:

Respectfully,
Henry

By ssbn727 (*****)

Date 12-11-2014 20:12

"Besides the strength of the filler metal in the joint, the overall strength of the joint or assembly (tube, fitting and joint) following the joining operation must also be considered when choosing whether to use soldered or brazed joints. As discussed, by definition the temperature that defines the difference between soldering and brazing of copper is approximately 840°F/449°C. This temperature is much more important than just an arbitrary definitional threshold. It is important because 700°F/371°C is the temperature at which copper begins to anneal, or be changed from hard temper (rigid) to annealed temper (soft). With this change in temper comes an inherent loss in strength - hard temper copper is stronger than annealed temper copper. The overall amount of annealing that occurs, and thus strength that is lost, is determined by the temperature and the time the material spends at that temperature. The higher the temperature, the less time it takes to change from hard temper to soft temper.

Since brazing temperatures must exceed the melting point of the brazing alloys, between 1,150°F/621°C and 1,550°F/843°C, the process of making a brazed joint causes the base metals to anneal or soften, resulting in a reduction in the overall strength of the assembly. While a brazed joint is demonstrably stronger than a solder joint, the Rated Internal Working Pressure, that is the 24/7 allowable working pressure of the system, is lower for annealed tube (see Copper Tube Handbook, Tables 3a through 3e)." - The link below:

http://www.copper.org/applications/plumbing/cth/technical-data/

In this link below there's a chart that shows how E - modulus of elasticity starts @ approximately 17 million psi with the temperature around minus 300 degrees F and then continues to lessen through ) zero degrees F where it's down to 16 million psi and as one continues to follow the line that represents Cu in the chart... The modulus of elasticity - E drops even further to approximately 13.5 million psi @ 700 degrees F which is also where the line ends so any higher in temperature it would probably drop even further and faster...Here's the chart:

http://www.engineeringtoolbox.com/young-modulus-d_773.html

If I find something else, I'll post it here.

Respectfully,
Henry