Effect of thermo-mechanical treatment on properties improvement and microstructure changes in copper–gold alloy

• The anneal hardening effect appeared in Cu-4.5Au alloy.
• The increase in properties during the annealing was achieved through two hardening stages.
• Significant microstructural changes occurred during the thermo-mechanical treatment.
• EDS analysis showed a significant change in the concentration of gold atoms within the grain.

This paper reports on the changes in hardness, microhardness, electrical conductivity and microstructure using the optical and scanning electron microscopy of the copper-based alloy with 4.5 at.% gold, during the complex thermo-mechanical treatment, which is used to create the conditions for development of anneal hardening effect. It was shown that the increase of deformation degree during both the prefinal and final rolling resulted in the increase of hardness, microhardness and electrical conductivity values, due to changes in the microstructure caused by the cold plastic deformation. The differences in the initial microstructure of the homogenized and quenched samples created the different deformation strengthening rates. Low-temperature annealing of the finally rolled samples contributed to a further increase of the above properties due to the anneal hardening effect. The improvement of the properties during the annealing was accomplished in two stages, and the best combination of properties was achieved in the second stage of hardening after annealing at 260 °C. Minor changes in the microstructure were noticeable during the annealing at 260 °C, but the EDS analysis showed a significant change in the concentration of gold atoms within the grain.