Effects of Mg17Al12 phase on microstructure evolution and ductility in the AZ91 magnesium alloy during the continuous rheo-squeeze casting-extrusion process

•A novel and compact processing route integrates rheo-squeeze casting with extrusion.•Homogenization was unnecessary, and a high extrusion ram speed of 7 mm/s was obtained.•Ultrasonic vibration results in an uneven spread of Al in primary and secondary grains.•Microstructural hereditary laws between as-cast billets and as-extruded rods were revealed.•The Mg17Al12 fibrous bands showed the particle-stimulated nucleation (PSN) effect.