Microstructure Evolution and Corrosion Resistance of As-Extruded AZ91–Ca Alloy During Friction Stir Back Extrusion

In this research, the influence of extrusion speed during friction stir back extrusion on the microstructure, mechanical properties, and corrosion resistance of AZ91–Ca alloy wires was investigated. Our findings reveal that the grain size increased after friction stir back extrusion, and uniform-sized grains formed on both the surface and at the core of the extruded wires. As the extrusion speed increased from 40 to 80 mm/min, the average grain size of the extruded wires decreased from 24.3 ± 2.7 to 21.9 ± 2.1 μm. Conversely, reducing the extrusion speed from 80 to 40 mm/min resulted in a decrease in the average hardness from 76.36 ± 0.96 to 73.06 ± 0.78 HV0.1. The maximum yield strength and ultimate tensile strength in the sample created with an extrusion speed of 80 mm/min are 183.96 ± 10.91 and 238.56 ± 10.42 MPa, respectively. Notably, the corrosion rate decreased by 9.1% and reached 1.19 mm/year as the extrusion speed increased from 40 to 80 mm/min.