ABSTRACT
Alloys that are rich in manganese have better castability due to their lower melting points and greater fluidity. Bearing in mind that 6% manganese is equivalent to 1% aluminium, the equivalent aluminium content of copper–manganese-aluminium system is 2% higher than actual. The solubility of manganese in the α-phase above 650°C is 8%, whereas that in the ß phase at 650°C is 26% and increases sharply with temperature. The light etching α-phase is a copper–rich solid solution with a face-centred cubic (fcc) space lattice arrangement. The dark etching ß phase is a copper–rich solid solution with an aluminium content approximately twice that of the α-phase. Manganese also lengthens considerably the time of transformation of ß into the α+γ2 eutectoid and lowers to 400°C the temperature at which it takes place. Manganese-aluminium bronze alloys experience only limited corrosive attack which is concentrated in certain more anodic phases.
