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GUIDE TO INDENTIFICATION OF BASE METAL ALLOYS
The easiest way to identify an
alloy is by color. Scratch away oxide, paint, or other surface cover to expose bare
metal, then narrow the range of identities following these guidelines:
 | Copper is reddish brown.
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| Brass high in zinc is yellow,
otherwise it is reddish and harder than copper.
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| Aluminum, magnesium, zinc, tin and
lead are silvery.
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| Gray cast iron shows dark gray on
the surface of a scratch or fracture. Robbed with a finger, the skin picks up a gray
graphite streak.
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| White cast iron is silvery white
on a fracture surface.
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| High carbon steel chips have
edges that are lighter in color than those of low-carbon steel. It is harder to cust
than is low-carbon steel.
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| Manganese steel chips are blue
and non-magnetic.
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The flame test uses the flame of
a welding torch. Under the flame, the sharp edge of an aluminum die
casting is slow to melt, because aluminum dissipates heat rapidly. The edge of a zinc
die casting starts to melt quickly.
Magnesium filings
burn with a sparkling white flame. Deoxidized copper melts under a
flame, electrolytic copper does not.
If lead boils out of a bronze
alloy under heat, the material is free-machining bronze. If no boiling occurs, the
material is ordinary bronze.
Rubbing with a metal file gives
some indication of the hardness of a material. Hardness testing, Brinell or
Rockwell, gives an idea of carbon content and tensile strength of steels.
Chemical kits help identify
metals. The kits contain nitric acid, sulfuric acid, wood alcohol, phosphoric acid,
hydrochloric acid, zinc chloride and other chemicals.
In the spark test, size, shape
and color of sparks given off when the test piece is ground indicates the base metal type.
Use of a magnet to check magnetic
properties is a quick way to narrow pissible identification:
| Magnetic metals: Carbon steel,
nickel steel, low-alloy steels, cast iron, malleable iron, straight-chromium stainless
steel.
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| Slightly magnetic metals: Monel,
work-hardened manganese steel, work-hardened austenitic stainless steel, high ferritic
stainless steel.
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| Non-magnetic metals: Manganese
steel, bronze, nickel-silver, austenitic stainless steel, aluminum, brass, bronze, zinc
alloys, aluminum alloys, magnesium alloys, lead, tin.
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