Increasing the Operating Temperatures of High-Strength Wrought Al-Zn-Mg-Cu Alloys by Means of Doping with Transition Metals

The effect of doping with scandium, zirconium, and hafnium on the thermal stability of high-strength wrought Al-Zn-Mg-Cu (of 7XXX series) alloys at 80 degrees & Scy; for 100 hours is investigated. The study is performed on rods produced by a two-stage hot extrusion of 1500 g ingots. As shown, the doping with scandium and zirconium has improved the hardness and strength characteristics due to the occurrence of two ensembles of dispersed precipitates: intermetallics eta '-phase (MgZn2) and Al3(Sc1-xZrx) particles coherently bonded with the aluminium matrix. As proved, in the 7XXX alloy, which is additionally doped with the (Sc + Zr + Hf) complex, the composition of nanosize precipitates based on Al3Sc intermetallic compound includes zirconium and hafnium. The alloying of the base alloy with the complex (Sc + Zr + Hf) stabilizes the structural state of the alloy and, after holding at 80 degrees & Scy;, no significant changes in the size and distribution of strengthening particles are observed. This makes it possible to obtain high strength characteristics of Al- Zn-Mg-Cu alloys with a high level of plasticity at long-term holding at 80 degrees & Scy;.