Effect of mechanical milling on microstructure evolution and mechanical properties of Al–Zn–Mg–Cu–Si alloy fabricated via spark plasma sintering

We investigated the effect of high-energy ball milling (HEBM) on the microstructure and mechanical properties of powders and spark plasma sintered samples of an Al–Zn–Mg–Cu–Si alloy. HEBM produced a nanocrystalline powder with an average grain size of 0.16 μm while increasing the amount of solid solution and the formation of fine amorphous aluminium oxide. The sintered alloy without HEBM consisted of η-Mg(Zn,Cu,Al)₂, T-Mg₃₂(Al,Zn)₄₉, β-Mg₂Si, and Q-Al₅Cu₂Mg₈Si₆ phases. The grain size of the sintered alloy decreased from 2.66 to 0.40 μm due to the application of HEBM. The amorphous aluminium oxide phase in the milled powder was transformed into MgO particles during sintering. The formation of MgO particles caused the depletion of Mg solid solutions, which resulted in the formation of Mg-free phases during sintering. High-energy ball milling (HEBM) improved the microhardness of the sintered alloy from 94 to 134 HV owing to grain refinement and the formation of fine secondary phases and MgO particles.