Copper is soft, ductile and takes a scratch from almost anything, including its own swarf. The published route is close to the aluminium one and for the same reasons, and it ends on an alkaline oxide step.

Why copper and copper alloys are difficult

It is soft and it deforms rather than cuts

Pure copper is among the more difficult metals to prepare well precisely because it is easy to prepare badly — it takes a bright finish quickly, and that finish is frequently a smeared layer rather than a polished one.

Twinning is part of the microstructure and also a preparation artefact

Annealing twins are a real and expected feature of brass and of annealed copper. Mechanical twins introduced by heavy-handed preparation look similar enough to matter. Low late-stage force is the difference between reading the structure and reading your own handling of it.

Alpha-beta brass has two phases with different hardnesses

As with duplex steel, any step long enough to level one phase begins to relieve the other. The short times below are not an economy measure.

The published route

Akasel publishes this sequence for copper and copper alloys. The figures are theirs. Times are quoted for a 300 mm preparation system and forces for a single 40 mm diameter sample.

Step	Surface	Abrasive or suspension	Speed	Force	Time
1 — plane grinding	Rhaco Grit	Water	300 rpm	20 N	Until plane
2 — fine grinding	Aka-Largan 9	DiaUltra, 9 µm	150 rpm	30 N	3:30 min
3 — diamond polishing	Aka-Moran-U	DiaUltra, 3 µm	150 rpm	25 N	2:30 min
4 — oxide polishing	Aka-Chemal	Fumed Silica Suspension, 0.2 µm	150 rpm	15 N	2:00 min

Source: Akasel Aka-Brief #1, Copper and Copper Alloys, 2022 edition, page 1. Every figure in this table is printed on that page; none of them is ours.

Where the method and this catalogue differ

We say what the method specifies and what we list, and we do not put the nearest thing we sell in its place.

Water — no consumable — the disc runs under water.

Reading the sequence

The shape of the route says more than any single number in it. This part is our reading, not a manufacturer statement.

The same shape as the aluminium route, with the same reasoning. SiC paper for plane grinding at 20 N, a 9 µm rigid-disc stage, a 3 µm cloth stage, then oxide. Both metals are soft, ductile and embedding-prone, and the published answer is the same answer.

The final step uses fumed silica rather than colloidal. This brief specifies fumed silica for the last step where the aluminium brief specifies colloidal. Both are oxide suspensions; the figures printed below are the ones the copper brief states.

Expect to re-polish if the sample sits. Copper tarnishes. A surface prepared today and examined tomorrow is not the surface you prepared. Dry it properly and examine it promptly, or plan to return to the final step.

The same sample, after each step

Akasel photographs the same specimen after every stage of this route and publishes the images on page 2 of Aka-Brief #1. We have not reproduced them here. The titanium guide shows what that sequence looks like for a material we do hold the images for.

Scaling it to your machine

Smaller platen, longer steps. The maker’s guidance is to add roughly a third to the times on a 250 mm system and to double them on a 200 mm one. The abrasive does the same work over less swept area.
Bigger samples, more force; smaller samples, less. The quoted loads are per 40 mm mount. Scale with mounted area rather than guessing, and if your machine cannot deliver the figure, extend the step instead of exceeding it.
Head speed is fixed. 150 rpm on the sample holder throughout, constant across every published method in this series.

What the route needs

6 consumables, and the sequence does not work without them:

Where these figures come from

The preparation route is Akasel’s, published in Akasel Aka-Brief #1, Copper and Copper Alloys, 2022 edition, page 1. The reading of it — why the sequence is shaped this way, what goes wrong, what to watch — is ours, and it is an interpretation rather than a manufacturer statement. We have not run this method in our own laboratory and we do not claim to have. Where the method calls for something we do not list, the guide says so above rather than substituting the nearest thing we sell.

Sources

Akasel Aka-Brief #1, Copper and Copper Alloys, 2022 edition, page 1 — every figure in the step table.
Akasel product pages and data sheets, cited row by row on each linked product page.
The reading of the method, and everything under “Why” and “Reading the sequence”: P2 Industrial.

Preparing copper and copper alloys for metallography