{ "title": "Metallography of copper and copper alloys insight", "kind": "reference", "company": "Struers", "category": "Lapping, honing & superfinishing", "parameters": { "Language": "English" }, "language": "en", "source_url": "https://www.struers.com/en/knowledge/materials/copper", "content_html": "

Metallographic preparation of copper and copper alloys

Copper is commonly used in a wide range of industries. However, its extreme ductility makes it prone to deformation and scratches. On this page, you can learn how to prepare scratch-free copper samples for metallographic examination quickly and effectively.

Download the full application note

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The main characteristics of copper and its alloys

Copper is a pliable metal that is easy to shape and form. Its attractive color, corrosion resistance and high electrical and thermal conductivity mean it is widely used in the electronics, automotive, building, chemical, and food and beverage industries.

With increasing purity, the electrical and thermal conductivity of copper increases. Pure, or oxygen-free, copper is only used in very specific applications.

Common industrial uses of copper include:

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The copper production process

Although metallic copper occurs naturally, it is mainly extracted from sulfide ores in a metallurgical smelting process. There are four main steps.

1. An initial smelting process extracts copper concentrates, resulting in copper matte (75 % Cu).
2. In a converter, air is blown into the liquid matte to oxidize the sulfides, resulting in blister copper (96-98 % CU).
3. Blister copper is refined in an anode furnace, resulting in anode copper (99 % Cu).
4. Impurities (including Ni, Pb, Ag, Pd and Au) are removed through electrolytic refining, resulting in copper cathodes (99.99 % Cu).

A small amount of copper is also produced by hydro-metallurgical process.

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Fig. 1: Copper with red copper oxides, dark field, 500x

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Fig. 2: Oxygen-free copper, etched with ammonium peroxydisulfate, 100x

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Fig. 3: Copper cathode, etched according to Klemm, 100x

Copper alloys

There is a large number of copper alloys, with zinc (brass) and tin (bronze) being the most common.

Brass (copper-zinc alloys)
Brasses are copper alloys with 5-45 % zinc. As copper has a high solubility for zinc, the alloys are very homogenous. With increasing zinc content, the reddish copper color changes to the yellow of brass. The brass also becomes harder and easier to machine.

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By adding aluminum, manganese, iron, nickel, tin or even small amounts of lead, special types of brass with specific chemical or mechanical properties can be produced.

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Fig. 4: α- brass, color etched, 200x

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Fig. 5: α-β brass cast (CuZn40Pb2) with grey-blue lead inclusions, unetched, 500x

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Fig. 6: α-β brass cast, etched according to Klemm, light α- solid solution in dark matrix of β- solid solution, 100x

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Bronze (copper-tin alloys)
Bronzes are divided into three types: wrought alloys, cast alloys, and bell casts. Depending on the required properties, small amounts of zinc, phosphorus, lead, nickel or iron can be added.

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Some specific brass alloys and their properties
Gun metal (Cu-Sn-Zn)Good corrosion resistance; a low friction coefficient
Aluminum bronzes (up to 11 % aluminum)High strength at elevated temperatures; very good corrosion resistance
Beryllium bronzeHigh strength; high hardness; does not produce sparks when striking or impinging other metals
Copper-nickel alloysExcellent corrosion resistance
Copper-nickel-zinc alloys (German silver)High strength; good corrosion resistance; easy to form
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Fig. 7: Aluminum bronze, color etched according to Klemm, pol. light, 200x

The metallography of copper and its alloys

When working with copper and its alloys, metallography is generally used for grain size measurement, as well as to perform purity checks by qualifying and quantifying the copper oxide content.

In certain brasses, it may be necessary to determine the distribution of lead, as this can influence the machining process.

In cast alloys, metallography is generally used for general structure evaluation, to assess the distribution of eutectic or lead, and to evaluate the presence of shrinkage cavities or porosity.

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Fig. 8: Bronze cast (CuSn10), etched with iron (III) chloride, dendritic structure α-δ eutectoid, 200x

Challenges in the metallography of copper and its alloys

Pure copper is soft and ductile, which makes it easy to deform and prone to scratches. Even bronzes and some of the harder brasses may be susceptible to severe scratching. This creates a problem for the metallographer. However, there are some simple solutions:

- Avoid coarse grinding abrasives
- Give a thorough diamond polishing with soft cloths
- Use chemical-mechanical fine polishing

Read on for a detailed description of how to prepare copper and its alloys for metallographic analysis quickly and accurately, without scratches or deformation.

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Fig. 9: Pure copper wire, with final polish of OP-S, DIC, 200x

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Fig. 10: Same sample as Fig. 9 with final polish of OP-S-ammonia/water/hydrogen peroxide mixture, DIC, 200x

Preparation of copper and its alloys: Cutting & mounting

The cutting and mounting of copper and its alloys are fairly simple.

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Find out more

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Preparation of copper and its alloys: Mechanical grinding & diamond polishing

With increasing purity, copper becomes softer and more susceptible to mechanical deformation and scratches. Consequently, grinding can cause deep deformation in high purity copper, while grinding and polishing abrasives can be pressed into the surface.

Copper alloys are harder, but still have a tendency to form scratches. In some bronzes, these scratches may occur in some individual grains only.

Note: The preparation data given below are for automatic grinding and polishing of 6 mounted samples, 30 mm in diameter, clamped into a holder.

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Mechanical grinding

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Plane grinding should be carried out with the finest possible grit in order to avoid any excessive mechanical deformation.

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Pure copper and copper alloys with low alloying contents

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Diamond polishing

Copper and its alloys should be diamond polished until all deformation and embedded abrasives from mechanical grinding have been removed. Chemical-mechanical fine polishing with silicon dioxide should result in an almost scratch-free surface.

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Final polish for pure copper and copper alloys: The polish/check sequence

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Fig. 11: α-β brass cast, mechanically polished, unetched, 200x

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Fig. 12: Same specimen as Fig.11 electrolytically polished, unetched, 200x. The lead inclusions are pulled out and therefore appear larger and more numerous

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Electrolytic polishing

Electrolytic polishing is suitable for pure copper and α- brass wrought alloys. Two-phase α-β brass can also be polished electrolytically, but the results are not suited to quantitative analysis, especially if the alloy contains lead. Due to the different phases, cast alloys are not suited to electrolytic polishing.

Before electrolytic polishing, fine grinding with SiC foil/paper up to 2400# or 4000# must be performed.

Discover the parameters for electrolytic polishing of copper in our Application Note here

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Etching of copper and its alloys

There are numerous etchants for copper and its alloys that are relatively easy to apply. Most cast alloys are not difficult to etch. However, it can be difficult to find the right etching solution for some wrought alloys, especially if they have been severely cold worked. In these cases, a color etch can be useful.

It is important to note that lead is attacked by the etchants and only black voids will remain after etching. Therefore, micrographs to document the quantity and distribution of lead must be taken before etching. The color of pure lead is grey-blue.

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Fig. 13: Bronze cast (CuSn8Pb), unetched, showing large and small blue-grey lead inclusions, pale blue α-δ eutectoid discernable, 500x

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Fig. 14: Same specimen as in Fig.13, color etched according to Klemm. The dendritic structure with light blue eutectoid and blue lead inclusions can be seen, but small lead inclusions cannot be clearly differentiated, 500x

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Fig. 15: Bronze cast (CuSn10), etched with iron (III) chloride, dendritic structure α-δ eutectoid, 200x

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ApplicationEtchant
Grain area etch for copper, brass and bronzes100 ml water. 10 g ammonium peroxydisulfate. Use fresh!
All types of copper100-120 ml water or ethanol. 20-50 ml hydrochloric acid. 5-10 g iron (III) chloride. (concentration variable)

Grain boundaries
Grain areas		25 ml distilled water. 25 ml ammonia water. 5-25 ml hydrogen peroxide, 3%
Less hydrogen peroxide
More hydrogen peroxide
α-β brass120 ml water. 10 g copper (II) ammonium chloride. Add ammonia water until precipitate dissolves
Fast and good polish for pure copper100 ml water. 100 ml ethanol. 19 g iron (III) nitrate
Colour etch according to Klemm100 ml cold saturated sodium thiosulfate. 40 g potassium metabisulfit
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Download the application note to see the full preparation method

Summary

Due to its good formability, high electric and thermal conductivity and corrosion resistance, copper is found in a wide range of industries and applications, from electric engineering and electronics to the food and beverage industry.

The metallography of copper and its alloys is used in quality control, mainly to check purity and grain size determination. In addition, cast alloys are examined for general structure evaluation. As copper is soft and ductile, it is particularly prone to mechanical deformation. Therefore, the finest possible grit must be used for the first mechanical grinding step.

For successful preparation of copper and copper alloys with mechanical grinding, it is suggested that:

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Get the full application note

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Want to read the full application note on the metallographic preparation of copper and its alloys? Download it here

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If you would like to learn more about the materialography of other metals and materials, check out our materials pages.

For specific information about the metallographic preparation of Copper, contact our application specialists.

Metallography of copper and copper alloys insight | Struers.com

Find all you need about the metallography of copper and copper alloys – including how to prepare scratch-free copper samples for metallographic analysis – with expertise and insight from Struers, the world’s leading materialographic and metallographic experts.

", "summary": "Find all you need about the metallography of copper and copper alloys – including how to prepare scratch-free copper samples for metallographic analysis – with expertise and insight from Struers, the world’s leading materialographic and metallographic experts.", "sections": [], "updated_at": "2026-10-17" }