The metallographic preparation of copper pipe welds- Trojan (Suzhou) material technology Co., Ltd.

The metallographic preparation of copper pipe welds

03-03-2023

Pure copper is an important non-ferrous functional material with excellent electrical and thermal conductivity, corrosion resistance and processing properties, but its high melting temperature greatly limits its application in the field of welding. Adding phosphorus to copper can significantly reduce its melting temperature and improve its brazing process performance. Copper-phosphorus solder is widely used for brazing copper and copper alloys, silver and silver alloys, molybdenum and molybdenum alloys, etc.

01 Cutting
Since it is necessary to observe the welding seam of the copper pipe, use the TableCUT-200 Automatic precision cut-off machine to cut it in half along its longitudinal axis.

TableCUT-200 Automatic precision cut-off machine

Equipment	TableCUT-200 Automatic precision cut-off machine
Consumables	SiC cutting blade
Parameter	3000rpm，0.15mm/s

02 Mounting-cold mounting
Prepare TJ2210 acrylic resin powder and curing agent in proportion, and place the sample in a ThetaMount Pressure Cold Mounting Machine for pressure curing after pouring;

ThetaMount Pressure Cold Mounting Machine

Acrylic resin

Equipment	ThetaMount Pressure Cold Mounting Machine
Consumables	TJ2210
Parameter	0.2MPa，15min

03 Grinding
Use Alpha-600 automatic grinding and polishing machine to grind the sample, sandpaper: P800→P2500；

Alpha-600 Automatic Grinder&Polisher

Metallographic abrasive paper

Equipment	Alpha-600 Automatic Grinder&Polisher
Consumables	Abrasive paper：P800；P1200；P2000；P2500
Parameter	Pressure: 15N，speed:130rpm，time:2min

04 Polishing-rough polishing
Use Alpha-600 Automatic Grinder&Polisher to polish the sample, use YS polishing cloth with 3μm polycrystalline diamond suspension for rough polishing;

YS-JP White Fiber Polishing Cloth(PSA)

Polycrystalline diamond suspension

Equipment	Alpha-600 Automatic Grinder&Polisher
Consumables	YS-JP White Fiber Polishing Cloth，3μm polycrystalline diamond suspension
Parameter	Pressure:20N，same direction speed：150rpm，time:3min

05 Polishing-fine polishing
Use Alpha-600 Automatic Grinder&Polisher to polish the sample, use ZN polishing cloth with 0.05μm silica polishing liquid for fine polishing.

Black Polyurethane Polishing Cloth(PSA)

Silica Polishing Fluid

Equipment

Alpha-600 Automatic Grinder&Polisher

Consumables

ZN-ZP Black Polyurethane Polishing Cloth，0.05μm Silica Polishing Fluid

（Add 25 % ammonia and 3 % hydrogen peroxide）

Parameter

Pressure: 15N，same speed and direction:120rpm，time:1~2min

06 Observation

Equipment	MN 60 series microscope
Consumables
Parameter	50×→500×

07 Analysis

Copper phosphorus
weld 50×

Copper phosphorus
weld 100×

Copper phosphorus
weld 200×

Copper phosphorus
weld 500×

Copper tubes have thin walls and low strength, so they are not suitable for hot mounting.

Copper is softer, use lower pressure when grinding.

It is difficult to remove copper scratches by simple mechanical polishing, so chemical mechanical polishing should be performed during fine polishing, and ammonia and hydrogen peroxide should be added to the silica polishing solution.

The base metal of the weld is pure copper, and it can be seen that it contains twin grains; the interdiffusion layer between the copper-phosphorus solder and the base metal is obvious; the weld structure is the primary Cu solid solution and the eutectic structure of Cu solid solution and Cu₃P.