A Study of the Constitution Heat Treatment and Mechanical Properties of Several Duplex and Complex Aluminium Bronzes.

The effect has been studied of quenching in water and oil, of air-cooling, and of subsequent tempering, on several binary, ternary and quaternary hypo-eutectoid aluminium bronzes. Jominy tests, and 5/16" square bars were used to study the effect of mass on depth hardening, and finally, mechanical properties were determined on selected combinations of alloys and heat-treatments. The hypo-eutectoid binary alloys showed that the maximum hardness obtained varied from that of the lowest aluminium content water-quenched to the highest hypo-eutectoid alloy air-cooled, oil-quenching sometimes giving the maximum hardness. Tempering caused considerable increases in hardness when carried out at 300-400°C. For the complex alloys, the highest hardness was given by oil-quenching, followed by water-quenching, with air-cooling giving little hardening. Again, tempering gave a marked peak hardness at 400°C, and in the case of two alloys, a narked secondary peak at 600°C. The water-cooled Jominy tests showed a soft quenched end (correspending to the water-quenched specimen) followed by a rise to a peak hardness (approximating to the tempered hardness) followed by a precipitation, and, a decrease to the air-cooled hardness. The results obtained on all alloys are ascribed partly to the martensitic transformation beta→beta', and partly to ageing which may take place during a slot cooling rate (e.g., oil-quenching), possibly due to a varying solubility line for the a phase. The behaviour during isothermal transformation can also be explained in this way, except where the aluminium content is high enough to allow eutectoidal decomposition to take place. Determinations of mechanical properties show that isothermally transformed specimens, for the same hardness, give lower elongation