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Biodegradable magnesium-based alloys are very promising materials for temporary implants. However, the clinical use of magnesium-based alloys is often limited by rapid corrosion and by insufficient mechanical stability. Here we investigated RS66, a magnesium-based alloy with extraordinary physicochemical properties of high tensile strength combined with a high ductility and a homogeneous grain size of ~1 μm which was obtained by rapid solidification processing and reciprocal extrusion. Using a series of in vitro and in vivo experiments, we analyzed the biodegradation behavior and the biocompatibility of this alloy. In vitro, RS66 had no cytotoxic effects in physiological concentrations on the viability and the proliferation of primary human osteoblasts. In vivo, RS66 cylinders were implanted into femur condyles, under the skin and in the muscle of adult rabbits and were monitored for 1, 2, 3, 4 and 8 weeks. After explantation, the RS66 cylinders were first analyzed by microtomography to determine the remaining RS66 alloy and calculate the corrosion rates. Then, the implantation sites were examined histologically for healing processes and foreign body reactions. We found that RS66 was corroded fastest subcutaneously followed by intramuscular and bony implantation of the samples. No clinical harm with transient gas cavities during the first 6 weeks in subcutaneous and intramuscular implantation sites was observed. No gas cavities were formed around the implantation site in bone. The corrosion rates in the different anatomical locations correlated well with the local blood flow prior to implantation. A normal foreign body reaction occurred in all tissues. Interestingly, no enhanced bone formation could be observed around the corroding samples in the condyles. These data show that RS66 is biocompatible, and due to its interesting physicochemical properties, this magnesium alloy is a promising material for biodegradable implants., (Copyright © 2013 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.)

Strength-ductility trade-off is a common issue in Mg alloys. This work proposed that a synergistic enhancement of strength and ductility could be achieved through tuning interlayer dwell time (IDT) in the wire and arc additive manufacturing (WAAM) process of Mg alloy. The thermal couples were used to monitor the thermal history during the WAAM process. Additionally, the effect of different IDTs on the microstructure characteristics and resultant mechanical properties of WAAM-processed Mg alloy thin-wall were investigated. The results showed that the stable temperature of the thin-wall component could reach 290 °C at IDT=0s, indicating that the thermal accumulation effect was remarkable. Consequently, unimodal coarse grains with an average size of 39.6 µm were generated, and the resultant room-temperature tensile property was poor. With the IDT extended to 60s, the thermal input and thermal dissipation reached a balance, and the stable temperature was only 170 °C, closing to the initial temperature of the substrate. A refined grain structure with bimodal size distribution was obtained. The remelting zone had fine grains with the size of 15.2 µm, while the arc zone owned coarse grains with the size of 24.5 µm. The alternatively distributed coarse and fine grains lead to the elimination of strength-ductility trade-off. The ultimate tensile strength and elongation of the samples at IDT=60s are increased by 20.6 and 75.0% of those samples at IDT=0s, respectively. The findings will facilitate the development of additive manufacturing processes for advanced Mg alloys. [ABSTRACT FROM AUTHOR]

A detailed and systematic investigation on the effect post heat treatment has on the microstructure evolution and the resultant mechanical properties of the wire arc additive manufacturing processed Mg-5.9Gd-2.8Y-0.7Zr alloy is conducted in this work. The microstructure of the as-built sample is composed mainly of fine equiaxed α-Mg grain and Mg24(Gd, Y)5 phase. The solution heat treatment (400°C × 1 h) has relatively little effect on grain size, but it can effectively reduce the content of the Mg24(Gd, Y)5 phase, which leads to a significantly improved elongation with slightly decreased strength. Further ageing heat treatment at 200°C induces prismatic β' precipitates formation and does not influence other phases and grain size. The samples directly following the peak ageing heat treatment process demonstrate the best tensile properties with yield strength of 227 ± 9 MPa, ultimate tensile strength of 350 ± 4 MPa and elongation of 5.5 ± 0.6%. [ABSTRACT FROM AUTHOR]

Abstract: In course of a study of high strength, ductile alloys based on the Mg–Li system, we have identified a new quaternary phase with a composition of Mg31Zn26Ca13Li8. The structure of this phase was investigated by Transmission Electron Microscopy (TEM) using the Convergent Beam Electron Diffraction (CBED) technique. Full atomic model is proposed using direct methods applied to powder X-ray diffraction data. The phase has a cubic primitive unit cell with lattice parameter a = 9.386(8)Å and its crystal symmetry belongs to the (No. 200) space group. The unit cell of the new phase exhibits a new structure type, which is a variant of the Mg2Zn11 structure. The reliability factors characterizing the Rietveld refinement procedure are: R p = 8.6%, R wp = 12.4%, R B = 6.9% and R f = 4.4%. [Copyright &y& Elsevier]

The thin-wall Mg-3.82Y-2.46Nd-0.56Zr (WE43) alloy component was fabricated using cold metal transfer-based wire arc additive manufacturing technology (WAAM-CMT) and the way in which microstructure evolution influences the corresponding mechanical properties in different height zones was studied. The thin-wall WE43 alloy component was mostly composed of fully equiaxed grains that had low texture strength. As a result of the layer-by-layer deposition, its microstructure exhibited obvious layer characteristics, mainly including melt pools (MP) with coarse equiaxed grains and melt pool boundaries (MPBs) with fine equiaxed grains. The grain size of the thin wall in the building direction decreased from 25.3 ± 1.2 µm in the bottom zones to 22.3 ± 0.7 µm in the top zones, whereas the content of the second phase increased. No obvious anisotropy was observed in the mechanical properties of the thin wall. The top zone specimens were found to have the best mechanical properties with ultimate tensile strength (UTS) of 233 MPa, yield strength (YS) of 153 MPa and elongation (EL) of 10.4%. In comparison to the bottom zone specimens, improvement in the mechanical properties of the top zone specimens resulted from secondary phase strengthening and grain boundary strengthening. ● The fully equiaxed grain microstructure and low base texture strength of Mg-Y-Nd alloys fabricated by WAAM. ● No obvious anisotropy in the tensile properties of the thin wall was observed. ● The cold material transfer technology and oscillation treatment resulted in low heat input and melt pool disturbance. [ABSTRACT FROM AUTHOR]