Engineering Materials
Duralumin contains

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
4 to 4.5% magnesium, 3 to 4% copper and rest aluminium
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

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Engineering Materials
Points of arrest for iron correspond to

Stages at which further heating does not increase temperature for some time
Stages at which allotropic forms change
Stages at which properties do not change with increase in temperature
There is nothing like points of arrest

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