Effect of Trace Silver on Precipitation Behavior of Strengthening Phases and Mechanical Properties of Aluminum-Copper Alloys

The effects of trace silver (Ag) on the precipitation behavior of strengthening phases and the mechanical properties of Al-Cu alloys have been investigated by performance testing, scanning electron microscopy, and transmission electron microscopy. Ag retarded the aging response of the Al-Cu alloys. The density of the θ′′ and θ′ phases decreased with increasing Ag content in under- and peak-aged alloys, and there was almost no θ′ phase in the 0.12 wt.% Ag alloy in the under-aged state. The θ′ phase morphology was narrower and longer after addition of Ag. Fatigue striations became more obvious and their spacing reduced at the fracture surface of experimental alloys with increasing Ag content, reflecting an improvement in the fatigue life of the alloys. On addition of 0.06 wt.% or 0.12 wt.% Ag, the fatigue life of the Al-Cu alloys was increased by 72.7% and 155.5%, respectively.