(a)   Aluminum† and its Alloys

Common Name

Reagent

Applications and remarks

Kellerís reagent

2-5% nitric acid

1-5% hydrochloric acid

0-5% hydrofluoric acid

Water

Widely applicable to aluminum alloys. Concentration of constituents in reagent can be varied to obtain desired effect. Primarily used for grain flow, porosity, cracks, etc.

Tuckerís reagent

3 parts (vol.) nitric acid

9 parts (vol.) hydrochloric acid

3 parts (vol.) hydrofluoric acid

5 parts (vol.) water

As Kellerís reagent

Anodic treatment

Anodizing solutions

(i)                  Following anodizing, wash to remove anodizing solution, but do not seal (i.e. by drying in hot water rinse). Allow to stand for 24 hours. Cracks and flaws such as porosity are revealed by brown stains.

(ii)                Will also reveal grain flow, particularly on forgings, bar and plate material.

 

(b). Copper and its alloys

 

Concentrated nitric acid

Grain etch, suitable for roughly prepared surfaces.

Alcoholic ferric chloride

25-60g ferric chloride

2-30ml hydrochloric acid

Alcohol

General purpose macroetch. Surface generally needs to be prepared to a moderately high standard. With high acid concentrations it is best to replace the alcohol with water in which case the solution becomes aqueous ferric chloride. Best used fresh.

 

(c) Magnesium and its alloys

 

2% ammonium

pershulphate

10% tartaric acid in water

Grain flow in forgings. Can replace the tartaric acid with citric, acetic, oxalic, and nitric acids.

 

(d) Ferrous alloys

Sulphur printing

3% sulphuric acid in water

Prepare steel surface to about 600 emery, soak photographic paper in reagent, remove surplus reagent from paper with blotting paper, and apply the photographic paper to the prepared steel surface. Allow 2-3 min, then remove and fix in normal photographic fixer. Brown coloration indicates sulphide segregation.

Steadís reagent

10g cupric chloride

40g magnesium chloride

20ml hydrochloric acid

(conc.)

Alcohol to 1L

Dissolve salts in acid with min. addition of water. Make up to 1 L with alcohol. Phosphorus segregation is unattacked, also reveals dendritic structure of cast steels.

Fryís reagent

90g cupric chloride

120ml hydrochloric acid

100ml water

Strain lines in mild steel are revealed by heating the sample to about 500F for 10-15min, prior to etching. Use a swab.

Humphreyís reagent

120g copper ammonium

chloride

50ml hydrochloric acid

1 L water

Pre-treat surface of sample with an 8% copper ammonium chloride solution then immerse sample in reagent for 1 to 2 hours. Copper deposit is loosely adherent and is removed with a fine abrasive. Shows dendrite structure of cast steels.

 

140ml hydrochloric acid

3 ml sulphuric acid

50 ml water

Immerse specimen in reagent at 200F for 15-30 min. deep etch reveals segregation, porosity, cracks, etc.

 

10g ammonium

persulphate

90ml water

Use with swab. Reveals variations in crystal structure, grain growth.

 

10ml nitric acid (conc.)

90ml water

Use with swab. Reveals variations in crystal structure, grain growth.

10% natal

10% nitric acid in alcohol.

May need up to 1h immersion. Reveals cracks, porosity, grain, etc. Specimen should be prepared to about 400 grit emery.

 

(e) Nickel base alloys

Aqua regia

50% Nitric acid

50%acetic acid

1 volume nitric acid

3 volume hydrochloric acid

General purpose reagent.

 

(f) Lead base alloys

Russellís reagent

(a)    80ml nitric acid in

220ml water

(b)   45g ammonium
molybdate in 300 ml
water.

Mix equal parts of (a) and (b) immediately before use. Grain contrast etch.

 

10 g ammonium molybdate

25g citric acid

100ml water

Bright etch for revealing grain structure, defects, etc.

 

(g) Zinc base alloys

 

Concentrated hydrochloric acid

Grain contrast etch.

 

5% hydrochloric acid in alcohol

General purpose etch.