Duralumin is an alloy made mainly from aluminium with small amounts of copper and manganese. Explain why duralumin is more suitable than pure aluminium for use in aircraft construction.

Pure aluminium has a regular crystal lattice of atoms of the same size, so the layers can slide over each other easily, giving it low strength. In duralumin the small amounts of copper and manganese atoms are of different size, which disturbs the regular lattice and creates lattice strain. This distortion hinders the movement of dislocations and prevents the layers from sliding, so the alloy is harder and stronger than pure aluminium. The increased strength makes duralumin more suitable for aircraft construction.