Copper and Copper Alloys - Metallographic Preparation Guide

Preparation Guide

Key points in sample preparation:

1、Cutting

Copper and copper alloys have low hardness and are prone to deformation. The cutting rate and feed rate of the cutting blade should be reduced during cutting. Silicon carbide cutting blades are generally recommended for cutting.

Silicon carbide resin cutting disc

2、Mounting

In most cases, copper and copper alloys are adequately mounted with a general-purpose phenolic hot mounting resin.

In the absence of a hot mounting machine, epoxy or acrylic cold mounting kits can be used for mounting.

MW001 general hot mounting resin

MC006 Flash Solid Universal Cold Mounting Kit

3、Grinding and polishing

Pure copper is very soft and prone to mechanical deformation and scratches; when grinding and polishing, abrasive particles can easily embed into the material surface.

Starting from rough grinding, coarse particles should be avoided as much as possible. It is recommended to start with finer silicon carbide sandpaper, such as 400#/600# for rough grinding. For larger copper alloy castings, you can start with 320# sandpaper. The pressure during grinding should be as small as possible.

The polishing of copper and copper alloys must be done with diamond polishing liquid to remove deep scratches.

Using OS001-JP aluminum oxide 0.05μm for chemical-mechanical fine polishing can obtain a surface with almost no scratches. The fine polishing liquid is especially recommended.

OS001-JPAlumina Nano-suspension Grinding and Polishing Liquid 0.05μm PCX Porous Neoprene Polishing Cloth

Electrolytic polishing is particularly suitable for pure copper and alpha brass wrought alloys. Two-phase alpha-beta brasses can also be Electrolytic polishing. However, the results are not very suitable for quantitative analysis, especially when lead is present in the alloy.

The step of grinding & polishing		Coarse Grinding	Coarse Grinding	Diamond Coarse Polishing	Diamond Coarse Polishing	oxide polishing
1	Surface	SiC sandpaper	SiC sandpaper	PCY Wool fabric	PCV Red Short velvet	PCX Neoprene
2	Abrasive Granularity	400#	800#、1200#、4000#	3μm	1μm	0.05μm
3	Polishing/ Lubricant	water	water	DS001 High performance polycrystalline diamond suspension	DS001 High performance polycrystalline diamond suspension	OS001-JP Silicon dioxide polishing liquid
4	Pressure	30N	25N	25N	20N	15N
5	Rolation speed	300	300	150	150	150
6	Time/min.	1	2	3~5	2~3	2~5

The above recommended parameters are taken from: Preparation method of Ø30 mm copper and copper alloy samples with Ø250 mm working plate on automatic grinding and polishing machine Smoothneer-6.

Etching

Commonly used chemical etching reagents for copper and copper alloys are as follows：

No	Name	Compositiol	UsageRang	Remark
1	Nitric Acid Aqueous Solution	Nitric acid 20~50ml Water 80~50mL	Processing copper, brass, bronze andcupronickel (add a small amount ofacetic acid to corrode cupronickel)	The reagent composition can be changedaccording to the alloy composition and state. Thsample should be shaken or wiped in the solutiolIf there is a dirty film on the surface, it can bescrubbed with dilute nitric acid vinegar solutior
2	Ferric chloride hydrochloric acid aqueoussolution	Hydrochloric acid 20~50ml Ferric chloride 10g Water (or methanol)120mL	Processing copper and brass	The surface roughness value should be low andthe grain contrast should be obvious
3	Chromic anhydride Ammonium chloride Nitricacid Sulfuric acid Aqueous solution	Chromic anhydride 0g Ammonium chloride 7.5g Nitric acid 50ml Sulfuric acid 8mL Water 100mL	Silicon Brass and Bronze	Clear grain

Commonly used chemical etching reagents for copper and copper alloys are as follows：

Name

composition

Remark

Ferric chloride hydrochloric acid aqueous
solution

Ferrous chloride 1g

Hydrochloric acid 5ml

Water 100mL

Take a small amount of solution and sprinkle it on thepolishing disc along with the polishing liquid to polishthe sample.
The above method can accelerate the polishing effectand eliminate the deformation (disturbance layer)structure and scratches produced by the sample duringgrinding. For single a copper, the effect is significant

The electrolytic etching solutions for copper and copper alloys are as follows：

Name

composition

Remark

备注

Orthophosphoric acid aqueous solution

5%~10%orthophosphoricacid aqueous solution

Voltage: @1~4V: ②1~8VTime: 10s; ②5~7s

①Pure copper

②Casing copper, free cutting copper, naval brassand jewelry copper alloy

Ferous sulfate, sodium hydroxide, sulfuric acidaqueous solution

Ferrous sulfate 30g