Improving thermal management materials is critical to many industries including the microelectronics where smaller components lead to larger heat densities. Performance of thermal management materials are largely governed by the thermal conductivity of the material. Commercial diamond particles have a very high thermal conductivity, but their inclusion into conductive metals such as copper is challenging due to a lack of compatibility which creates a poor interface between materials. This study uses a powder metallurgy approach employing an alloyed powder blend to act as an agent to improve the interface leading to improved thermal properties. Results show that minor additions of zirconium to the copper matrix is successful in improving the interface and allows for improvement of thermal conductivity up to a maximum of 533 W/m K with 40 vol.% diamond. Energy-dispersive X-ray spectroscopy mapping analysis shows that additions of zirconium are vastly better than chromium for improvement of interface. It is shown that caution must be taken when adding alloying elements because small additions result in a rapid decrease in conductivity of the alloy before diamonds are added.