Microstructural evolution of gas atomized Al-Zn-Mg-Cu-Zr powders during semi-solid rolling process

Under H2 atmosphere, the green strips were prepared from Al-5.8Zn-1.63Mg-2.22Cu-0.12Zr (mass fraction, %) powders by the semi-solid rolling process with a relative density from 76.1% to 88.0%. The role of temperature on microstructure and mechanical properties was investigated. With increasing rolling temperature from 580 to 610 °C, the disappearance of primary powder boundary and isolated pores, inter-diffusion of species and the change of grain boundary were accelerated. Moreover, the mechanism of microstructure evolution changes from the densification dominant regime to the coarsening dominant regime; the amount of η (MgZn2) phase decreased and more Al2Cu particles precipitated at grain boundaries. The optimum temperature for semi-solid rolling of Al-5.8Zn-1.63Mg-2.22Cu-0.12Zr powders was determined. The liquid fraction in the range of 53% to 67% corresponds with a high density level of green strips. The present experimental analysis suggests that semi-solid powder rolling can be optimized to manufacture strips with high mechanical properties.