Increased precipitation hardening response in Al-Si-Cu based aluminum casting alloy with In trace addition

Abstract The influence of In trace addition on the microstructure and hardening response for the A319-type aluminum casting alloy has been studied using thermodynamic calculations and high-resolution transmission electron microscopy. Indium addition to Al-8Si-1.5Cu (wt. %) alloy increases both in the aging rate and in the hardening magnitude by about 20 % (90 HV vs 75 HV). High-resolution transmission electron microscopy has revealed that the increased hardness is caused by the previously unidentified spherical shape “super” nanoprecipitates formed by three different phases: the θ' phase and most likely pure silicon Si and indium In.