Accumulative spin-bonding (ASB) as a novel SPD process for fabrication of nanostructured tubes

Research highlights: → High strain rate without considerable temperature rise accompanied by a high value of Zener-Hollomon parameter is achieved by ASB. → An average grain thickness and length of 186 and 419 nm are developed accompanied by increase of the grain boundary misorientation by four cycles of ASB. → While the hardness is increased from the inner regions to the outer ones, its homogeneity is increased with increase of the ASB cycles leading to decrease of the ratio of tensile strength to yield strength and consequently to decrease of the uniform elongation → The yield and tensile strengths of the material are significantly increased up to the values of 194 and 235 MPa, respectively. - Abstract: A novel SPD process for manufacturing of high strength tubes and cylinders by accumulative spin-bonding (ASB) is proposed. It is demonstrated that due to incremental deformation in this process, high strain rate without considerable temperature rise is achieved. This is accompanied with a high value of Zener-Hollomon parameter as a characteristic of this SPD process. ASB was applied to a commercially pure aluminum up to four cycles and its effects on the microstructure and mechanical properties were examined by optical microscopy, TEM, EBSD, microhardness and tension tests. The results show that ultra-fine grains are developed during the process by formation of subgrains at early stages followed by increase of the misorientations at later stages. This leads to a nanostructure with average grain thickness and length of 186 and 419 nm, respectively. It is indicated that while the hardness of outer regions is more than the inner ones, the hardness and its homogeneity is increased with the ASB cycles. Periodical presence of external layers within the thickness and consequent hardness saturation are responsible for this hardness evolution. As a result of grain refinement and the scheme of hardness development, the yield and tensile strength of material are significantly increased. Moreover, the ratio of the yield strength to the tensile strength and consequently the uniform elongation is decreased with the ASB cycles.