A comparative study on microstructures of a high-Zn AlZnMgCuZr alloy fabricated by casting and melt spinning

A high-Zn Al-27Zn-1.5Mg-1.2Cu-0.08Zr alloy was prepared by traditional casting and melt spinning. The ascasted alloy consists of well-developed alpha-Al dendrites with many coarse-phase and low solute concentration, coarse network precipitates at grain boundaries and the alpha-Al/-phase eutectic structures at triple junctions. Due to these featured structures, the as-cast alloy exhibits a low tensile strength of 101 MPa with room temperature and high temperature (300 degrees C) damping capacity of 0.0058 and 0.027 respectively. Comparatively, the as-spun alloy reveals gradient cross-sectional microstructures after solidification: an ultrafine grained region near the wheel surface, a transition region and an equiaxed-grained region near the ribbon free surface, with changes of precipitate morphologies from granular shape to network shape via vermicular. High-density nano-sized '-phase/GP-zones within alpha-Al grains result in a higher tensile strength (121 MPa) of as-spun alloy with room temperature and high temperature (300 degrees C) damping capacity of 0.0049 and 0.048 respectively. Fracture analysis shows that the as-casted alloy fails in a mixed-mode fracture, comprised predominantly of transgranular fracture, quasi-cleavage fracture, cleavage fracture and dimple fracture, whereas the as-spun alloy failed in cleavage fracture and dimple fracture.