On the microstructure and mechanical property of as-extruded Mg-Gd-Y-Zn alloy with Sr addition

In this study, microstructure evolutions of Mg-6Gd-3Y-0.1Zn-xSr (x=0, 0.2, 0.6) alloys (named as sample 0Sr, 0.2Sr, 0.6Sr) during heat-treatment and extrusion were investigated. As-cast sample 0Sr contains typical long period stacking ordered (LPSO) phases and MgRE. With Sr addition, amounts of LPSO phases decrease and are gradually replaced by the MgSr phases. After homogenization and annealing treatment, profuse strip LPSO phases readily precipitate in grain interiors of sample 0Sr, while only MgSr and MgRE phases are detected in samples 0.2Sr and 0.6Sr. It suggests that the Sr addition would inhibit LPSO phases. After extrusion, the bimodal grain structures, the bulk and strip LPSO phases are detected in sample 0Sr, which can contribute to providing strengthening and extra strain hardening. In as-extruded sample 0.2Sr, finer recrystallized grain size, bulk MgSr and LPSO phases (micron-scale) and MgRE phase (nano-scale) are found due to the pre-annealing treatment. However, lower amounts of both nano-sized and macro-sized LPSO phases lead to the low ultimate strength (300 MPa). In sample 0.6Sr, the strip LPSO phases are readily formed even though the length and total amounts of LPSO phases decrease. More bulk MgSr phases and LPSO phases are also precipitated, which lead to the more superior yield and ultimate strengths of 0.6Sr sample under higher temperature, as compared with the 0Sr sample

Editorial: Hexagonal close-packed metals and alloys: Processing, microstructure and properties

In comparison with face-centered cubic (FCC) and body-centered cubic (BCC) metals and alloys, hexagonal close-packed (HCP) metals and alloys show distinct characteristics, such as atomic site occupation, anisotropic microstructure, and fewer slip systems, owing to their HCP lattice structure. Therefore, HCP metals and alloys have distinguished processing, microstructure, and properties. Several types of HCP metals and alloys, involving titanium, zirconium, magnesium, and so on, are extensively used in a variety of industrial and military sectors. Up to date, an increased requirement is still needed to improve the understanding of the relationships among processing, microstructures, and the resultant properties of HCP metals and alloys. In the meantime, surface modification may be conducted on the HCP metals and alloys to obtain better surface properties. However, many challenges are still open for the surface modification of HCP metals and alloys. In the contents of this topic, many endeavors are made to highlight the recent advances related to the processing methods (including surface modification), microstructures, and properties of HCP metals and alloys

Homogenization and growth behavior of second-phase particles in a deformed Zr-Sn-Nb-Fe-Cu-Si-O alloy

Homogeneous distribution of fine second-phase particles (SPPs) fabricated by cycles of deformation and annealing in zirconium alloys is a critical consideration for the corrosion resistance of fuel claddings. Different deformation degrees of zirconium alloys would result in distinctive microstructures, leading to a distinct growth of SPPs during subsequent annealing. Unfortunately, the homogenization and growth behavior of SPPs in deformed zirconium alloys have not been well studied. In this work, a β-quenched Zr–Sn–Nb–Fe–Cu–Si–O alloy was rolled and annealed at 580◦C or 680◦C. The morphologies, distributions, and sizes of SPPs resulting from the different processing procedures were investigated. A linear distribution of SPPs is found in the β-quenched sample. Afterward, SPPs grow and are randomly distributed during heat treatment as the deformation degree or annealing time (or temperature) increases. The homogenization and growth of SPPs are attributed to the Ostwald ripening mechanism that is governed by lattice diffusion and short-circuit diffusion. The sample with a higher deformation degree is speculated to have a larger number of defects that provide more shortcuts for the mass transfer of SPPs, thereby facilitating a homogeneous distribution of fine SPPs during annealing

Homogenization and growth behavior of second-phase particles in a deformed Zr-Sn-Nb-Fe-Cu-Si-O alloy

Homogeneous distribution of fine second-phase particles (SPPs) fabricated by cycles of deformation and annealing in zirconium alloys is a critical consideration for the corrosion resistance of fuel claddings. Different deformation degrees of zirconium alloys would result in distinctive microstructures, leading to a distinct growth of SPPs during subsequent annealing. Unfortunately, the homogenization and growth behavior of SPPs in deformed zirconium alloys have not been well studied. In this work, a β-quenched Zr–Sn–Nb–Fe–Cu–Si–O alloy was rolled and annealed at 580◦C or 680◦C. The morphologies, distributions, and sizes of SPPs resulting from the different processing procedures were investigated. A linear distribution of SPPs is found in the β-quenched sample. Afterward, SPPs grow and are randomly distributed during heat treatment as the deformation degree or annealing time (or temperature) increases. The homogenization and growth of SPPs are attributed to the Ostwald ripening mechanism that is governed by lattice diffusion and short-circuit diffusion. The sample with a higher deformation degree is speculated to have a larger number of defects that provide more shortcuts for the mass transfer of SPPs, thereby facilitating a homogeneous distribution of fine SPPs during annealing

Corrosion behavior and characteristics of passive films of laser powder bed fusion produced Ti-6Al-4V in dynamic Hank’s solution

The corrosion behavior of laser powder bed fusion produced (L-PBF-produced) titanium alloys involving flowing body fluid is still unclear. Therefore, this work investigates in vitro corrosion behavior and the characteristics of passive films formed on L-PBF-produced Ti–6Al–4V in both static and dynamic Hank’s solutions. Electrochemical measurements, immersion tests, X-ray photoelectron spectroscopy and scanning electron microscopy were conducted. In comparison to the L-PBF-produced Ti–6Al–4V in static Hank’s solution, the samples showed lower charge transfer resistance and higher passivation current density (anodic current density as well) in dynamic Hank’s solution. Meanwhile, a more apparent deposition of apatite and hydroxyapatite is found on the L-PBF-produced Ti–6Al–4V in dynamic Hank’s solution. Such outcomes mainly result from the enhancement of film/solution interfacial transportation in dynamic Hank’s solution. The dynamic Hank’s solution provides more calcium and phosphate ions to the surface of the passive film and also takes away the dissolved metal ions. Therefore, more salt deposition and a lower-quality passive film are found