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In this study, a novel method, Tubular Channel Angular Pressing-Extrusion (TCAPE), is introduced for manufacturing ultrafine microtubes. This method, integrating Tubular Channel Angular Pressing (TCAP) and microtube extrusion (MTE) processes, reduces the number of stages in the fabrication of ultrafine microtubes while achieving favorable mechanical properties. In the TCAPE process, the tube undergoes Severe Plastic Deformation (SPD) in the shaping region and is subsequently shaped into the desired geometric dimensions through the extrusion process at the end. To investigate the effect of the number of SPD passes on the microstructure and mechanical properties of the produced microtubes, one-pass and two-pass SPD were applied. Metallography, XRD testing, tensile testing, and hardness measurement were employed for analysis. For a one-pass SPD, the sample was processed only through the TCAPE process (TCAP + MTE), while for a two-pass SPD, the sample underwent the TCAP process first and then underwent TCAPE for the second processing step (2TCAP + MTE). Tensile test results indicate an increase in Ultimate Tensile Strength (UTS) from the initial value of 73 MPa–103.1 MPa and 148 MPa, and elongation altered from the initial value of 10 to 7.1 and 17.5 after two-pass SPD. Metallography results show a reduction in grain size from the initial value of 160 μm to 15 μm and 3 μm after two-pass SPD. The TCAPE process, due to applying higher strain (1.955) compared to the TCAP process (1.64), exhibits better performance in refining the microstructure and improving mechanical properties. The hardness and ultimate strength of the TCAPE-processed sample are 13.33% and 13.5% higher than those of the TCAP-processed sample, respectively.

In this study, the Cyclic Contraction-Expansion Extrusion (CCEE) process, a novel severe plastic deformation (SPD) technique, is applied to the AZ91 magnesium alloy to enhance its mechanical properties through microstructural refinement. The CCEE method combines cyclic expansion extrusion (CEE) and cyclic extrusion compression (CEC), integrating their advantages while overcoming drawbacks. The CCEE process is capable of inducing substantial plastic strain (3.38) within a single processing cycle, eliminating the need for secondary punches or a synchronized backpressure system. The process is conducted at a temperature of 300 °C, resulting in a bimodal microstructure through the dynamic recrystallization (DRX) mechanism. This microstructure consists of refined equiaxed α-Mg grains with an average size of 2.8 μm, surrounded by a network of newly nucleated α-Mg grains and Mg17Al12 particles with an average size of 500 nm in the two-pass processed sample. Results obtained from the tensile test technique indicate a significant enhancement in the ultimate tensile strength (UTS) of the AZ91 alloy, increasing from 139 MPa to 276 MPa and 290 MPa, and a notable improvement in elongation, increasing from 4% to 8% and 12% after two passes of the CCEE process. Macro-texture X-Ray diffraction (XRD) measurements reveal the formation of a pyramidal deformation texture in the one-pass sample, contributing to the UTS improvement. This texture weakens during the second pass, leading to an increase in elongation. Furthermore, microhardness measurements show an increase from HV 62 to HV 85 after the first pass of the CCEE and HV 73 after the second pass.