Mesoscopic structure control of spray formed high strength Al-Zn-Mg-Cu alloys

Several high solute, high strength 7xxx series aluminum alloys with solute contents close to equilibrium solid solubility limits of the Al-Zn-Mg-Cu system have been produced by rapid solidification using spray deposition (the Osprey process). This process yields massive preforms directly from the liquid state by combining atomization and consolidation into one step. Various elements, including chromium, manganese and silver are incorporated to produce a variety of microstructures and mechanical properties. The zinc to magnesium ratio is also varied to see the effect on the strength. Superior strengths in excess of 849 MPa are achieved and are attributed to two major substructures with different scale; nanometer sized η′ metastable precipitates and slightly larger, but finely distributed dispersoids which provide a fiber-like reinforcement. The remarkable strengthening is predominantly attributed to precipitation hardening and a large coherency strain.