Properties and microstructure changes in Au-Cu-based alloy with indium addition

In this work, the effects of indium addition on the microstructure, corrosion resistance and hardness in as-cast Au-Cu-based alloys were investigated. The experimental results indicated that as-cast Au-Cu-based shown a typical dendritic structure, and the secondary dendrite arm spacing of alloy was significantly decreased by adding indium element, especially when the In-rich phase existed at interdendritic region. The as-cast samples without indium and with 1 wt.% In were a single Au-Cu-based solid solution with face-centered cubic (f.c.c.) structure. Moreover, the In-rich phase of the alloy with 3 wt.% In shown granular structure, but with 5 wt.% In was network structure. With the indium content increasing, the hardness of alloy was significantly increased and exhibited better Hall-Petch type relationship with the secondary dendrite arm spacing. Minor indium addition enhanced the corrosion resistance of alloy, but when an In-rich phase generated at interdendritic region, the corrosion rate was increased due to the micro-galvanic effect and also affected by the structure of the In-rich phase.