Metal flowing and microstructure characteristics of the micro inner gear ring fabricated by rheological extrusion

The 2A50 aluminum alloy micro inner gear rings were fabricated using a rheological extrusion process. Metal flowing and microstructure characteristics of the micro inner gear rings in rheological extrusion were investigated by finite element simulation and experiments, respectively. The microstructures of the tooth, bottom land, and non-dentiform region were considered as representative sections of the inner gear ring. Results reveal that during the rheological extrusion process, the metal exhibited a continuous flow from the periphery toward the center of the billet along the radial direction, meticulously filling the tooth spaces of the mandrel. Concurrently, a gradual decline in flow velocity was observed. The grains in the teeth and bottom lands were fine and elongated along the flowing lines, whereas those in the non-dentiform region were similar to the semi-solid slurry with nearly equiaxed grains. The microstructure of the micro inner gear rings predominantly consisted of recrystallized grains and substructures. In non-dentiform regions, the proportion of recrystallized grains was remarkably higher than that of the substructure. The average grain size of the microstructure of the inner gear ring ranged between 14.04 and 20.05 μm. The grain size in the tooth was sensitive to the extruded temperature and showed an increment of approximately 36.3% when the temperature increased from 575 °C to 590 °C. This phenomenon suggests that low temperature in the semi-solid range was advantageous for the microstructure and mechanical performance of the inner gear ring. No pronounced texture was detected in the micro inner gear rings, and the peak intensity (4.81) in the pole figures was found in the bottom land at the extruded temperature of 590 °C, suggesting a relatively weak {112} < 126 > texture. This process recommends a propitious technique for the fabrication of components with microfeatures.