No abstract

D ue to low Young's modulus (~45GPa), low density (1.7-2.0 g•cm-3), and good biodegradable properties, magnesium and magnesium alloys are in a region of interest as potential orthopedic, craniofacial, and cardiovascular materials [1]. Many researchers are currently developing new biodegradable magnesium alloys and investigating all kinds of properties [2]. Among all the alloys, Mg-Zn-Ca especially attracts the scientists' attention because of their high strength (yield strength>200 MPa, ultimate tensile strength>250MPa), high ductility (elongation>20%), moderate bio-corrosion properties, and good biocompatibility [3, 4]. Summarizing the development status of Mg-Zn-Ca alloys, it is found that Zn content generally surpasses or equals to 4wt.% if Ca addition is less than 1wt.% [1,5-13] or Zn concentration <10wt.% if Ca addition is ≥1wt. % [14-20]. The purpose of high Zn addition is to ensure high mechanical properties by solid-solution strengthening, grain boundary strengthening and precipitation strengthening, while the role of Ca is to refi ne the grain size and enhance the ignition point [21]. However, it is also noted that high Zn or high Ca concentration is generally detrimental to corrosion resistance [15, 22-25]. Therefore, the growing trend in

No abstract

In the anastomotic surgery, the currently used degradable magnesium alloys are facing some bottleneck problems such as lower mechanical properties and slower degradation rate. In this study, the novel biodegradable extruded Mg-1Zn-0.2Ca-xAg (x=0, 1, 2, 4) alloys will be developed and the corresponding microstructure, mechanical, and corrosion properties after Ag addition will be investigated. The results indicate that with the Ag addition, the grain size is refined due to fully dynamic recrystallization and Ag 17 Mg 54 phase, an important strengthening phase, begin to be precipitated in the Ag-contained alloys. Due to the stronger solution strengthening and precipitation strengthening, the Mg-1Zn-0.2Ca-4Ag alloy attains the highest ultimate tensile strength among all the alloys. Moreover, Ag element also enhances the electrode potential of the matrix, reduces the susceptibility of pitting corrosion and accelerates the corrosion rate of the alloys by micro-galvanic corrosion between the second phases and the matrix from the analyses of corrosion products and 3D Volta potential map. As a result, 4Ag alloys attain the fastest degradation rate among all the alloys. Combing the mechanical and corrosion results, it can be seen that 4Ag alloys, as novel biodegradable magnesium alloys, can meet the requirement of anastomotic surgery preferably, exhibiting the better application prospects.

In this study ZK60/WE43 bimetal composite rods were manufactured by a special method of hot diffusion and co-extrusion. Interface microstructure, deformation mechanism, and yield asymmetry between tension and compression for the composite rods were systematically investigated. It was observed that the salient deformation mechanism of the ZK60 constituent was {10-12}<−1011> extension twinning in compression and prismatic slip in tension, and different deformation modes resulted in yield asymmetry between tension and compression. In contrast, the WE43 constituent tends to be more isotropic due to grain refinement, texture weakening, solid-solution and precipitation strengthening, which were deformed via basal slip, prismatic slip, and {10-12}<−1011> extension twinning in both tension and compression. Surprisingly, it was found that yield asymmetry between tension and compression for the ZK60/WE43 composite rods along the extrusion direction was effectively reduced with a compression-to-tension ratio of ~0.9. The strongly bonded interface acting as a stress transfer medium for the ZK60 sleeve and WE43 core exhibited the coordinated deformation behavior. This finding provides an effective method to decrease the yield asymmetry between tension and compression in the extruded magnesium alloys.