Effect of doping with refractory rare-earth metals on the structure and properties of Al–5Zn–3Mg alloys produced by powder metallurgy and casting methods

Abstract

The effect of doping with transition refractory metals on the structure and properties of Al–Zn–Mg alloys produced by different methods is studied. It is ascertained that the strength of cast alloys is increased by scandium and zirconium doping due to the modifying action of scandium that arrests recrystallization and precipitation of the fine-grained phase matrix-coherent Al3(Sc1–x Zr x ) phase; the strength of alloys obtained by powder metallurgy (P/M) methods increases to a smaller extent, in which the ultrahigh cooling rate of melt atomized by high-pressure water plays the basic role in forming the fine-grained structure. The strength of powder metallurgy alloys based on wateratomized powders is substantially higher than that of similar alloys produced by the conventional casting method (standard commercial cast alloys and alloys produced by granular technology). The advantages of P/M alloys over cast alloys are especially prominent in the absence of scandium doping. The highest strength of the P/M alloys with scandium (σb = 651 MPa and σ0.2 = 596 MPa) is shown by Al–5Zn–3Mg–0.5Mn–0.7Zr–0.3Sc. Among the P/M alloys without scandium, the highest strength is shown by Al–5Zn–3Mg–0.85Zr–0.22Cr–0.17Ni–0.15Ti alloy (σb = 618 MPa and σ0.2 = = 553 MPa).