Mechanical properties and thermal stability of hot-rolled Al–15%B 4 C composite sheets containing Sc and Zr at elevated temperature

Abstract

The microstructure, mechanical properties, thermal stability and tensile fracture of two hot-rolled Al-15 vol.% B₄C composite sheets (S40 with 0.4 wt.% Sc and SZ40 with 0.4 wt.% Sc and 0.24 wt.% Zr) were investigated. During multi-pass hot rolling, coarse Al₃Sc or Al₃(Sc, Zr) precipitations appeared and resulted in the loss of most of their hardening effect. In an appropriate post-rolling heat treatment, the hot-rolled sheets regained a significant precipitation hardening because of the precipitation of fine nanoscale Al₃Sc and Al₃(Sc,Zr) that uniformly distributed in the aluminum matrix. After the peak aging, the ultimate tensile strength at ambient temperature of the S40 and SZ40 sheets can reach 198 MPa and 215 MPa, respectively. During 2000 h of annealing at 300℃, the strengths at ambient temperature of both S40 and SZ40 composite sheets slowly decreased with increasing annealing time. However, the tensile strengths at 300℃ of both S40 and SZ40 composite sheets remained nearly unchanged and were less sensitive to the annealing time and more tolerable for precipitate coarsening, which demonstrated an excellent long-term thermal stability of both materials at elevated temperature. The tensile fracture at ambient temperature of both S40 and SZ40 composite sheets was dominated by the brittle B₄C particle fracture, whereas the interfacial decohesion of B₄C particles became the prominent characteristic of the fracture at 300℃.