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· For alloy compositions below the eutectic solubility limit (19.2 wt % Sn) the material enters the a-phase zone before reaching the eutectic temperature and has a polycrystalline substitutional solid solution structure.
· On further cooling (crossing the solvus line) the system enters the two phase a + b zone, and precipitates of the b-phase form in the a-phase matrix.
· Cooling to room temperature (in thermo-dynamic equilibrium) will alter the weight ratio of these two phases in accordance with the lever rule applied to this region.
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