Formation of Fine Spheroidal Microstructure of Semi-Solid Al–Zn–Mg–Cu Alloy by Hyperthermally and Subsequent Isothermally Reheating

摘要: The high strength 7xxx series aluminium alloys are usually difficult to be prepared as semi-solid feedstock, because some dispersoid particles (soluble only in liquid) could pin at grain and subgrain boundary make the alloy difficultly recrystallise. In this work, a novel multistep reheating regime is developed for recrystallisation partial melting (RAP) route prepare fine spheroidal microstructure of Al–Zn–Mg–Cu alloy. After 665 °C, holding 4 min subsequent isothermally 620 °C with total heating time 15 min, microstructures size ∼40 μm were without remained unrecrystallised grains directionality, which much finer than conventionally obtained (∼100 μm).