Effects of Ca on microstructure, mechanical and corrosion properties and biocompatibility of Mg–Zn–Ca alloys

Zn and Ca were selected as alloying elements to develop an Mg–Zn–Ca alloy system for biomedical application due to their good biocompatibility. The effects of Ca on the microstructure, mechanical and corrosion properties as well as the biocompatibility of the as-cast Mg–Zn–Ca alloys were studied. Results indicate that the microstructure of Mg–Zn–Ca alloys typically consists of primary α-Mg matrix and Ca₂Mg₆Zn₃/Mg₂Ca intermetallic phase mainly distributed along grain boundary. The yield strength of Mg–Zn–Ca alloy increased slightly with the increase of Ca content, whilst its tensile strength increased at first and then decreased. Corrosion tests in the simulated body fluid revealed that the addition of Ca is detrimental to corrosion resistance due to the micro-galvanic corrosion acceleration. In vitro hemolysis and cytotoxicity assessment disclose that Mg–5Zn–1.0Ca alloy has suitable biocompatibility.     

Effects of yttrium and zinc addition on the microstructure and mechanical properties of Mg–Y–Zn alloys

The effects of the yttrium and zinc additions on microstructure and mechanical properties of Mg–Y–Zn alloys were investigated. It was found that the addition of yttrium increases the eutectic temperature of Mg–Y–Zn alloys greatly. The addition of yttrium can also greatly increase the dynamic recrystallization (DRX) temperature of Mg–Y–Zn alloys. The volume fraction of DRX grains in Mg₉₇Y₂Zn₁ alloy is larger than that in Mg₉₆Y₃Zn₁ alloy but smaller than that in Mg_95.5Y₃Zn_1.5 alloy due to the effects of yttrium and zinc addition. The long period stacking (LPS) structures of 18R and 14H were observed in Mg–Y–Zn alloys. The increase in the yttrium content results in increase in strength and decrease in elongation in Mg–Y–Zn alloys. The increase in both yttrium and zinc contents results in increase in both strength and elongation in Mg–Y–Zn alloys. The high strengths of the alloys were thought due to the strengthening by the grain refinement, solid solution strengthening, strain strengthening, high density of plane faults of the LPS structures, and distribution of fine Mg₂₄Y₅ phase.     

Effect of Cu/Zn on microstructure and mechanical properties of extruded Mg–Sn alloys

In this paper, the effect of Cu and Zn addition on mechanical properties of indirectly extruded Mg–2Sn alloy was investigated. Mg–2Sn–0.5Cu alloy exhibits a moderate yield strength (YS) of 225?MPa and an ultimate strength of 260?MPa, which are much higher than those of the binary Mg–2Sn alloy, and the elongation (EL) evolves as ～15.5%. Mechanical properties of the Mg–2Sn–0.5Cu alloy are deteriorated with more 3 wt-% Zn addition, and YS and EL are reduced as 160?MPa and ～10%. The detailed mechanism is discussed according to the work-hardening rate and strengthening effect related to the grain sizes, second phases and macro-textures. Grain refinement and proper texture are believed to play a critical role in both strength and ductility optimisation.     

Structural characteristics and corrosion behavior of biodegradable Mg–Zn, Mg–Zn–Gd alloys

In this research, binary Mg–Zn (up to 3 wt% Zn) and ternary Mg–Zn–Gd (up to 3 wt% Gd, 3 wt% Zn) alloys were prepared by induction melting in an argon atmosphere. The structures of these alloys were characterized using light and scanning electron microscopy, energy dispersive spectrometry, X-ray diffraction and X-ray fluorescence. In addition, Brinell hardness measurements were taken to supplement these studies. Corrosion behavior was evaluated by immersion tests and potentiodynamic measurements in a physiological solution (9 g/l NaCl). Depending on the composition, structures of the as-cast alloys contained α-Mg dendrites, MgZn, Mg₅Gd and Mg₃Gd₂Zn₃ phases. Compared to pure Mg, zinc improved the corrosion resistance of binary Mg–Zn. Gadolinium also improved the corrosion resistance in the case of Mg–1Zn–3Gd alloy. The highest corrosion rate was observed for Mg–3Zn–3Gd alloy. Our results improve the understanding of the relationships between the structure and corrosion behavior of our studied alloy systems.     

Effects of Zn content on microstructures and mechanical properties of as cast Mg–Zn–Y–Zr alloys

Abstract

In the present work, the effects of Zn content on the microstructures and mechanical properties of as cast Mg–xZn–5Y–0·6Zr alloys (x?=?2, 5, 8 and 13 wt-%) have been investigated. The results show that the ternary Mg–Zn–Y phase compositions change with Zn/Y ratios induced by the change in Zn content. It is found that the fracture is mainly decided by the characteristics and distribution of second phase rather than the grain size. The influences of these phases, especially the W phase, on the mechanical properties of the alloys have been discussed. Both ultimate tensile strength (UTS) and elongation decrease with the increase in Zn content, while the instance of yield strength (YS) is just the reverse. The W phase is easily cracked because of its brittleness and easy to result in decohesion from the matrix because of the weak atomic bonding, which greatly degrade the UTS and elongation. It can be concluded that the YS closely depends on the grain size, while UTS and elongation closely depend on the volume fraction of eutectic compound (α-Mg+W phase).     

Effects of the enhanced heat treatment on the mechanical properties and stress corrosion behavior of an Al–Zn–Mg alloy

In this article, the effects of the enhanced solution treatment (EST) and high-temperature pre-precipitation (HTPP) on the microstructures, mechanical properties, and stress corrosion cracking resistance of an Al–Zn–Mg alloy have been investigated. The results indicated that EST and HTPP can substantially affect the microstructures of the alloy. The width of the continuously distributed grain boundary precipitates decreases after the EST, while the continuous grain boundary precipitation changes to a discontinuous precipitation structure after both the EST and HTPP. The yield strength, tensile strength, elongation, and fracture toughness of the specimens after the EST are much higher than those of the specimens only after traditional solution treatment, since the EST substantially decreases the size and volume fraction of the constituents. The stress corrosion cracking resistance of the specimens after both the EST and HTPP has been greatly improved due to the discontinuous distribution, and high Cu and low Mg concentrations of the grain boundary precipitates.     

Microstructure,mechanical and corrosion properties and biocompatibility of Mg–Zn–Mn alloys for biomedical application

Mn and Zn were selected to develop a Mg–Zn–Mn magnesium alloy for biomedical application due to the good biocompatibility of Zn and Mn elements. Microstructure, mechanical properties, corrosion properties and biocompatibility of the Mg–Zn–Mn alloys have been investigated by use of optical microscope, scanning electron microscope, tensile testing, and blood hemolysis and cell toxicity. Microstructure observation has shown that the addition of Zn and the extrusion significantly refined the grain size of both the as-cast and the extruded magnesium alloys, which mainly contributes to the high tensile strength and good elongation. Polarization test has shown Zn could accelerate the formation of a passivation film, which provides good protection to the magnesium alloy against simulate body fluid. Cell culture and hemolysis tests have shown that the magnesium alloy did not have cell toxicity, showing good cytocompatibility, but the alloy caused hemolysis to blood system. It was suggested that surface modification have to be adopted to improve the blood compatibility of the magnesium alloy for the application in blood environment.     

The influence of Gd content on the microstructure,mechanical properties,corrosion behavior and corrosion film deposition mechanisms of as-extruded Mg–Zn–Mn–Sr–Gd alloys for biomedical applications

Journal of Materials Science - The microstructure, corrosion behavior and corrosive film formation of as-extruded Mg–2Zn–0.4Mn–0.1Sr–xGd alloys (x?=?0, 0.5, 1...     

Effects of Sn on microstructure and mechanical properties of as-rolled Mg–5Zn–1Mn alloy

Effects of Sn on microstructure and mechanical properties of Mg–5Zn–1Mn alloy subjected to high strain rate rolling (9.1?s^-1), 300°C and 80% pass reduction are investigated. With higher Sn content, the dynamic recrystallisation (DRX) grain size gradually decreases due to the stronger pinning of nano-scale precipitates at grain boundaries and the DRX fraction first increases due to the enhanced effect on DRX by decreasing stacking fault energy and then decreases due to more precipitates at grain boundaries. Ultimate tensile strength (UTS) and elongation to rupture (Er) of as-rolled alloys increase and then decrease. Alloy with 0.9 mass% Sn exhibits the highest DRX fraction (95?vol.-%), the finer DRX grain size (1.22?µm), UTS of 358?MPa and Er of 20.4%.     

Effects of trace Er addition on the microstructure and mechanical properties of Mg–Zn–Zr alloy

The effects of trace Er addition on the microstructure in Mg–9Zn–0.6Zr alloy during casting, homogenization, pre-heating, and hot extrusion processes were examined. The mechanical properties of alloys with and without Er were compared. The results showed that Er exhibited a lower solubility in solid magnesium and formed thermally stable Er- and Zn-bearing compounds. The Er-bearing alloy exhibited a considerably improved deformability, as well as a fine and uniform microstructure. Moreover, dynamic precipitation of fine MgZn₂ particles with a modified spherical morphology occurred during hot extrusion, resulting in a tensile yield strength of 313 MPa and a high elongation to failure value of 22%. Further aging of the Er-bearing alloy led to an increment of another 30 MPa in yield strength. In addition, Er markedly increased the thermal stability of the alloy structure.     

Effects of samarium on microstructure and mechanical properties of Mg–Y–Sm–Zr alloys during thermo-mechanical treatments

Microstructure and mechanical properties of Mg–4Y–xSm–0.5Zr (x = 1, 4, 8) alloys during thermo-mechanical treatments were investigated in this study. Mg–4Y–4Sm–0.5Zr alloy exhibits higher tensile strength but lower elongation than Mg–4Y–1Sm–0.5Zr alloy during the thermo-mechanical treatments. Large amount of intermetallic phases still remained at grain boundaries in Mg–4Y–8Sm–0.5Zr alloy after solution. These undissolved phases can strengthen the grain boundaries at temperatures higher than 573 K. But the room temperature mechanical properties of Mg–4Y–8Sm–0.5Zr alloy during the thermo-mechanical treatments were greatly weakened for the brittleness of these undissolved intermetallic phases.     

Effects of Sc(Zr) on the microstructure and mechanical properties of as-cast Al–Mg alloys

Both the addition of 0.6% Sc and simultaneous addition of 0.2% Sc and 0.1% Zr exerted a remarkable effect on grain refinement of as-cast Al–Mg alloys, changing typical dendritic microstructure into fine equiaxed grains. Such effect was found to be related to the formation of primary particles, which acted as heterogeneous nucleation sites for α-Al matrix during solidification. Primary particles formed in Al–Mg–Sc–Zr alloy could be identified as the eutectic structure consisting of multilayer of ‘Al₃(Sc,Zr)?+?α-Al?+?Al₃(Sc,Zr)’, with a ‘cellular-dendritic’ mode of growth. In addition, an attractive comprehensive property of as-cast Al–5Mg alloy due to the addition of 0.2% Sc and 0.1% Zr was obtained.     

The microstructure and mechanical properties of as-cast Mg–4Y/Nd–2Zn alloys

Optical microscopy, scanning electron microscopy, X-ray diffraction and tensile testing were performed to investigate the microstructure and mechanical properties of as-cast Mg–4Y/Nd–2Zn alloys. The results show that the secondary dendritic arm spacing for the Mg–4Y–2Zn alloy is smaller than that for the Mg–4Nd–2Zn alloy, and that X-Mg₁₂YZn or W-Mg₃Zn₃Nd₂ form in Mg–4Y/Nd–2Zn alloys. The lamellar X phase distributes at the grain boundary, pointing into the grains, whereas the rod-like W phase preferentially segregates at the triangle junction of the grain boundary. The greater grain boundary strengthening effect and the smaller fragmentation effect of the brittle eutectic phases leads to the as-cast Mg–4Y–2Zn alloy having better comprehensive mechanical properties. The fracture mechanism for as-cast Mg–4Y/Nd–2Zn alloys is quasi-cleavage fracture.     

Effect of forging process on microstructure,mechanical and corrosion properties of biodegradable Mg–1Ca alloy

The performance of Mg–1Ca alloy, a biodegradable metallic material, may be improved by hot working in order that it may be of use in bone implant applications. In this study, Mg–1Ca cast alloy was preheated to different temperatures before undergoing forging process with various forging speeds. Macro- and microstructure of the samples were examined by stereo and scanning electron microscopes (SEM) equipped with energy dispersive X-ray spectroscopy (EDS), respectively. To determine the mechanical properties of the alloy, hardness value and plastic deformation ability of the samples were measured. To investigate the corrosion behaviour of the alloy, immersion and electrochemical tests were performed on the samples in simulated body fluid and the corrosion products were characterized by SEM/EDS. The results showed that increasing forging temperature decreased grain size led to improved hardness value and plastic deformation ability of the alloy, whereas no significant effect was observed by changing forging speed. Moreover, forging at higher temperatures led to an increase in the amount of Mg₂Ca phase at grain boundaries resulted in higher corrosion rates. It can be concluded that although forging process improved the mechanical properties of the alloy, it does not satisfy the corrosion resistance criteria required for bone healing.     

Effects of Zn on the microstructure,mechanical property and bio-corrosion property of Mg–3Ca alloys for biomedical application

The effects of the addition of Zn element on the microstructures, mechanical properties and bio-corrosion properties of Mg–3Ca alloys are investigated. The microstructure and X-ray diffraction topography indicate that as-cast Mg–3Ca alloys are composed of primary Mg and eutectic (α-Mg + Mg₂Ca) phases, while Mg–3Ca–2Zn alloys are constituted of primary Mg and eutectic (α-Mg + Mg₂Ca + Ca₂Mg₆Zn₃) phases. Mechanical properties results show that the element Zn could improve both tensile strength and elongation of Mg–3Ca alloys. The ultimate tensile strength is enhanced by 22%. Meanwhile, the corrosion resistance is increased by the addition of Zn element. It is thought that the presence of Ca₂Mg₆Zn₃ phase mainly contributes to these improvements. Mg–3Ca–2Zn alloy provides moderate strength and excellent corrosion resistance for biomedical application.     

Improvement of mechanical properties and corrosion resistance of biodegradable Mg–Nd–Zn–Zr alloys by double extrusion

Mg–Nd–Zn–Zr alloy is a novel and promising biodegradable magnesium alloy due to good biocompatibility, desired uniform corrosion mode and outstanding corrosion resistance in simulated body fluid (SBF). However, the corrosion resistance and mechanical properties should be improved to meet the requirement of the biodegradable implants, such as plates, screws and cardiovascular stents. In the present study, double extrusion process was adopted to refine microstructure and improve mechanical properties of Mg–2.25Nd–0.11Zn–0.43Zr and Mg–2.70Nd–0.20Zn–0.41Zr alloys. The corrosion resistance of the alloys after double extrusion was also studied. The results show that the microstructure of the alloys under double extrusion becomes much finer and more homogeneous than those under once extrusion. The yield strength, ultimate tensile strength and elongation of the alloys under double extrusion are over 270 MPa, 300 MPa and 32%, respectively, indicating that outstanding mechanical properties of Mg–Nd–Zn–Zr alloy can be obtained by double extrusion. The results of immersion experiment and electrochemical measurements in SBF show that the corrosion resistance of Alloy 1 and Alloy 2 under double extrusion was increased by 7% and 8% respectively compared with those under just once extrusion.     

Effect of the Zn content on the microstructure and mechanical properties of indirect-extruded Mg–5Sn–xZn alloys

Mg–5Sn–xZn alloys with varying Zn contents were subjected to indirect extrusion and the effects of the Zn content on the microstructure and mechanical properties of the as-extruded alloys were investigated. It was found that, the grain size and the basal texture are basically similar, however, the amount of fine particles consisting of Mg₂Sn and MgZn phases increases markedly as the Zn content increases. A higher number of these particles would be responsible for the better comprehensive mechanical properties as well as a lower degree of yield asymmetry.     

Microstructure,mechanical properties and machinability of Cu–Zn–Mg and Cu–Zn–Sb brass alloys

Lead-free alloys have attracted great attentions recently due to the toxic nature of lead for the human body. In this study, low amounts of Mg and Sb were added to the Cu65–Zn35 brass and microstructure, mechanical properties and machinability of samples were compared to Cu65–Zn35 brass. Both Mg and Sb led to the promotion of β′ phase as well as the formation of new ternary copper rich intermetallic particles. It was found that these particles had a significant role in the reduction of the ultimate tensile strength, toughness, work hardening and elongation while increasing the hardness of samples. Results of machinability evaluation of samples showed that the cutting forces were decreased significantly and morphology of chips were improved compared to Cu65–Zn35 brass sample.     

Effects of solution treatment on the microstructure and mechanical properties of Al–Cu–Mg–Ag alloy

The effects of solution treatment on the microstructure and mechanical properties of Al–Cu–Mg–Ag alloy were studied by optical microscopy (OM), scanning electron microscopy (SEM), energy dispersive X-ray (EDX), differential scanning calorimeter (DSC), transmission electron microscopy (TEM) and tensile test, respectively. The results show that the mechanical property increases and then decreases with increasing the solution temperature. And the residual phases are dissolved into the matrix gradually, the number fraction of the precipitation and the size of recrystallized grains increase. Compared to the solution temperature, the solution holding time has less effect on the microstructure and the mechanical properties of Al–Cu–Mg–Ag alloy. The overburnt temperature of Al–Cu–Mg–Ag alloy is 525 °C. The yield strength and the elongation get the best when the alloy is solution treated at 515 °C for 1.5 h, is 504 MPa and 12.2% respectively. The fracture mechanism of the samples is ductile fracture.