Liren Cheng

The hot deformation behavior of a Mg-9.2Er-4.9Sm-2.2Zn-0.6Zr (wt.%) alloy, with emphasis on the role of grain size and long-period stacking-ordered (LPSO) phases, was examined via comparison experiments. Two types of samples were obtained through distinct heat treatment schedules: sample A had a smaller grain size, featuring block-shaped LPSO phases at grain boundaries and lamellar LPSO phases within grains, while sample B had a larger grain size and few LPSO phases. The hot deformation behavior was characterized by the true stress–strain curve within the processing window of 300–450 °C and 0.001–1 s⁻¹. The block-shaped LPSO phases contributed more significantly to strain hardening, leading to elevated flow stress in sample A, particularly under low-temperature and high-strain-rate conditions. Through the particle-stimulated nucleation (PSN) mechanism, block-shaped LPSO phases demonstrated greater efficiency in promoting Dynamic recrystallization (DRX) compared to lamellar LPSO phases; additionally, the synergistic effect between LPSO phases and grain boundary density further improved DRX efficiency. During hot deformation, dynamic precipitation of both block-shaped and lamellar LPSO phases occurred. The formation of block-shaped phases required a longer duration than that of lamellar ones. The presence of the LPSO kink exerted an influence on DRX, while a significant angle kink can promote DRX.

Invasive tumors are difficult to be completely resected in clinical surgery due to the lack of clear resection margins, which greatly increases the risk of postoperative recurrence. However, chemotherapy and radiotherapy as the traditional means of postoperative adjuvant therapy, are limited in postoperative applications, such as multi-drug resistance and low sensitivity, etc. Therefore, an engineered magnesium alloy rod is designed as a postoperative implant to completely remove postoperative residual tumor tissue and inhibit tumor recurrence by gas and mild magnetic hyperthermia therapy (MMHT). As a reactive metal, magnesium alloy responds to the acidic tumor microenvironment by continuously generating hydrogen. The in-situ generation of hydrogen not only protects the surrounding normal tissue, but also enables the magnesium alloy to achieve MMHT under low-intensity alternating magnetic field (AMF). Furthermore, the numerous reactive oxygen species (ROS) produced by heat stress will combine with nitric oxide (NO) generated in situ, to produce more toxic reactive nitrogen species (RNS) storm. In summary, engineered magnesium alloy can completely remove residual tumor tissue and inhibit tumor recurrence by MMHT and RNS storm under low-intensity AMF, and the biodegradability of magnesium alloy makes great potential for clinical application.

Isothermal compression behaviors of as-extruded AA 2055 alloy (T6 state) were studied at temperature of 320, 380, 440 and 500 °C with strain rate of 0.001, 0.01, 0.1 and 1 s⁻¹ by a Gleeble-3800 testing machine. A modified Johnson–Cook model fitted by polynomial and power-exponential functions were established to describe the flow stress of the alloy. The constitutive models fitted by higher-order polynomials were more accurate than the ones fitted by second-order polynomial and power-exponential functions. The constitutive model fitted by a fourth-order polynomial was chosen for the optimal constitutive model in order to balance the prediction accuracy and model complexity. The modified Johnson–Cook constitutive model could predict the flow stress well, especially in high-temperature zone (around 500 °C) and low-temperature zone (around 320 °C). The dynamic precipitation and dissolution of the T₁ phase during hot compression were discussed. The unusual dynamic precipitation of the T₂ phase was investigated during hot compression by XRD and TEM. The massive dense fine precipitates effectively pinned dislocations or subgrain boundaries to accelerate DRV but suppressed DRX, leading to a low frequency of HAGBs in compressed samples.

Wrought AZ (Mg–Al–Zn) series alloys have attracted lots of researches, due to low cost, high strength and good formability. Few researches focus on creep characteristics of wrought AZ series alloys, which might be of significance to extensive use of low-cost wrought Mg–Al based alloy at elevated temperature. The microstructures, tensile properties and creep characteristics of as-extruded Mg-9Al-Zn-0.5RE-0.5Ca-0.5Si (wt.%, named AZXSE91000) alloy were investigated by optical microscopy (OM), scanning electron microscopy (SEM), X-ray diffractometer (XRD), TEM (transmission electron microscopy), tensile tests and tensile creep tests (40–100 MPa, 125–150 °C). The as-extruded AZXSE91000 alloy exhibited good tensile strength both at room temperature and elevated temperature. The co-addition of Si, Ca and rare earth elements can improve the heat resistance of as-extruded AZ91 alloy resulting from fragmented heat-resistant particles hindering grain boundaries sliding. The steady creep rates of as-extruded AZXSE91000 alloy can be comparable with that of as-cast AZ91 alloy under similar experimental conditions. Dislocation climbing and grain boundary slip should dominantly contribute to the creep of as-extruded AZXSE91000 alloy. The asymmetric discontinuous precipitation in crept samples revealed that diffusion played an unneglected role during the creep process.

The microstructures and tensile properties of as-cast and as-extruded Mg–4Sm–xZn–0.5Zr (x = 0, 1, 2, 3, 4 wt %) alloys were systematically investigated by optical microscope, X-ray diffractometer (XRD), scanning electron microscope (SEM) and transmission electron microscope (TEM). Numerous nanoscale dynamic precipitates could be observed in the as-extruded alloys containing high content of Zn, and the nanoscale particles were termed as (Mg,Zn)₃Sm phase. Some basal disc-like precipitates were observed in as-extruded Mg–4Sm–4Zn–0.5Zr alloy, which were proposed to have a hexagonal structure with a = 0.556 nm. The dynamic precipitates effectively pinned the motions of DRXed (dynamic recrystallized) grain boundaries leading to an obvious reduction of DRXed grain size, and the tensile yield strength of as-extruded alloy was improved. The as-extruded Mg–4Sm–4Zn–0.5Zr alloy exhibits the best comprehensive mechanical properties at room temperature among all the alloys, and the yield strength, ultimate tensile strength and elongation are about 246 MPa, 273 MPa and 21% respectively.