The General Process of Bright Annealing Copper and its Alloys

27 September 2021

To date, many heat treatment processes are being done to various metals and alloys for them to acquire property alterations and improvements. Once a material undergoes a heat treatment process, its physical and structural properties are expected to improve, allowing it to be processed further.

One heat treatment process that is common among metals and alloys is annealing. It is a process wherein the physical and sometimes chemical properties of a material undergo vital changes. Most of the time, this process allows the material to obtain increased ductility and reduced hardness, ensuring that it can be workable for other processes and procedures.

For copper, the process of bright annealing is typically conducted due to the benefits it can bring.

A Quick Overview of Bright Annealing

But before knowing the benefits of bright annealing, one must know how it works first. Bright annealing is normally carried out by annealing the material in a controlled-atmosphere furnace. The furnace being utilised by the process may possess certain sizes, temperatures, and cooling rates, ensuring that it can easily carry out the bright annealing process without any problems.

The bright annealing of copper and its alloys intends to protect them from oxidation. Hence, the furnace atmosphere system should possess less partial pressure than that necessary to generate the oxide. Oxygen reduction can likewise be achieved by exposing the atmosphere to an active gas like hydrogen. Additionally, utilising a non-flammable atmosphere as well as diluting any flammable component below its flammable limit must be done to avoid oxidation-related issues. Ultimately, oxidation problems and issues can be prevented through maximising zoning technology.

Aside from preventing oxidation, the furnace atmosphere system should be able to remove unwanted processing lubricants. This specific function can be done through physical flushing or exposing the lubricant through an atmosphere component.

Bright Annealing Copper and Its Alloys

One thing about copper is that it is difficult to oxidise. Hence, it is common for copper materials to be annealed with exogas or steam. However, the use of exogas in the annealing process will only generate carbon dioxide and soot. Annealing with steam, alternatively, can be costly. One non-toxic alternative to these two elements is the use of high-purity nitrogen and a small addition of hydrogen. 

For tough pitch copper, it is therefore recommended to be annealed in atmospheres that contain hydrogen of around 2%, preventing any instances of embrittlement. Annealing the copper with lower-purity nitrogen is also possible and can generate great results. The only problem with the use of hydrogen is that it can take some time. Without any intervention, the gas mixture may interact with the annealing process and just ruin the workpiece. To make things more efficient, it would be better for the gas mixture to pass over a catalyst before introducing it into the furnace.

Copper-based alloys that contain aluminium, beryllium, and zinc can also be annealed in a protective atmosphere system that consists of an exothermically generated gas. They can, however, utilise nitrogen/hydrogen mixtures to prevent toxicity and soot.

To know more about bright annealing, feel free to call us at Alpha Detroit Heat Treatment.

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