Microstructure and superior quenching sensitivity of a novel Sc, Zr alloyed Al-Zn-Mg-Cu alloy.

• Quench-hardening depth of a novel Al-Zn-Mg-Cu-Sc-Zr alloy exceeds 150 mm. • Quenching rate is reduced to 1.5 °C/s, the hardness loss value of the aged alloy is < 8%. • The Al 6 Mn and E phase promote heterogeneous precipitation of η phase. • The coherent Al 3 (Sc, Zr) and fine G.P zones effectively strengthen the studied alloy. This paper studies a novel Al-Zn-Mg-Cu-Mn-Sc-Zr alloy that exhibits outstanding quenching sensitivity with a quench-hardening depth of more than 150 mm. Jominy end quenching allows the alloy to obtain different quenching rates. The Brinell hardness of the aged alloy with a quenching rate of 27 °C/s is 154 HB; when the quenching rate drops to 1.5 °C/s, its hardness value loses about 8%, which is 142 HB. The quenching-induced equilibrium precipitates heterogeneously precipitated at the grain boundary and the incoherent phase interfaces (E phase, Al 6 (Mn, Fe) phase), but no heterogeneous precipitates are observed along the coherent L1 2 -Al 3 (Sc, Zr) particles. After artificial aging, densely distributed nano-scaled atomic clusters and G.P zones, as well as grain boundary precipitation free zones (PFZs) were observed. [ABSTRACT FROM AUTHOR]