Copper, bronze, brass

Aluminum bronze

phase diagram of the copper-aluminum
phase diagram of the copper-aluminum

Aluminum bronze - based alloys where the main alloying element is aluminum. Apply two-and multicomponent alloys. Phase diagram of the Cu-Al in the equilibrium state is shown in figure.


The figure shows that the maximum solubility of aluminum in solid copper is 9.4% (by weight). As the temperature increases from 565 to 1037 ° C the solubility of aluminum in the copper decreases and reaches 7.5%.
By the stable phase of Cu-Al are α, β, γ2 and α2 phase.
Phase α - primary solid solution that is isomorphic with the unit face-centered cubic crystal lattice. Onslow cooling the alloy to a temperature of 400 ° C α-phase forms a short-range order, which leads to a marked reduction in its electrical resistivity, which continues at a temperature below 200 ° C by eliminating the stacking fault.

Phaseβ - solid solution formed on the basis of the stoichiometric composition Cu3Al directly from the melt at a temperature of 1036-1079 °C, with a unit-centered cubic crystal lattice. Age β - malleable, electrically conductive and stable at temperatures above 565 ° C. Rapidcooling of the alloy (at a rate of> 2 ° C / min), it undergoes sharpmartensitic transformation type, forming the intermediate phase (Fig. 1). Byslow cooling (<2 ° C / min) β-phase is divided into eutectoid α + γ2form a coarse γ2 phase precipitating in the form of continuous chains, giving the alloy brittle. Ageγ2 (Cu9AI4), formed from the phase γ ', is stable at low temperatures, brittle and hard, with a conductivity lower than that of β-phase.

Ageα2, formed at 363 ° C as a result of reaction between the phases peritectoid α and γ2, has face centered cubic lattice, but with different parameters.

Metastablephases in alloys: β1 - from elementary centered cubic lattice (a - 5,84Å, Al - 11.9%), ordered; β '- with elemental face-centered cubic crystal lattice (Al - 11.6%), very deformed;β1 '- with elementary rhombic lattice (a = 3,67 Å, ​​a = 7,53 Å, Al - 11,8%), ordered; γ1-phase with the orthorhombic unit cell (a = 4.51 Å, a = 5,2 Å, a = 4,22 Å, Al - 13,6%), ordered. The existence of other phases, which are a kind of phase β1 '.