Strengthening and thermal conductivity behaviors of cast Cu-La-Zn alloys

A new Cu-La-Zn alloy system with high thermal conductivity was developed for die casting, and the thermal conductivity of this alloy system was 200-300 W/(m center dot K), which was twice as that of ordinary brass. The effects of Cu6La intermetallic compounds and Zn solute atoms on the strengthening and thermal conductivity behaviors were quantitatively studied in as-cast binary Cu-La (2.0-4.5 wt.% La) and ternary Cu-2La-xZn (0-3.0 wt.% Zn) alloys, respectively. The results showed that for the increase of per 1 wt.% La or Zn, the thermal conductivity decreased by about 34 W/(m center dot K). In Cu-2La-xZn alloys, the lattice constant of alpha-Cu matrix increased from 3.6163 to 3.6239 angstrom. Due to the solid solution strengthening of Zn atoms, the hardness of the alpha-Cu matrix showed a parabolically increasing tendency, from 1.495 to 1.597 GPa. According to the calculations of the Maxwell-Eucken model based on the microstructure, the thermal conductivity of Cu6La phase was determined to be about 35.37 W/(m center dot K), and the reduction in thermal conductivity of alpha-Cu matrix caused by Zn solute atoms was quantified to be 51.38 W/(m center dot K) per 1.0 at.% Zn increase.