Engineering Materials
A material is known as allotropic or polymorphic if it

Responds to heat treatment
Has a fixed structure under all conditions
Has its atoms distributed in a random pattern
Exists in several crystal forms at different temperatures

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Engineering Materials
Duralumin contains

3.5 to 4.5% copper, 0.4 to 0.7% magnesium, 0.4 to 0.7% manganese and rest aluminium
5 to 6% tin, 2 to 3% copper and rest aluminium
4 to 4.5% magnesium, 3 to 4% copper and rest aluminium
3.5 to 4.5% copper, 1.2 to 1.7% manganese, 1.8 to 2.3% nickel, 0.6% each of silicon, magnesium and iron, and rest aluminium

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