Sr Alloy Research Articles

Mechanical properties and biocorrosion behaviour of as-cast Zn-xCu-Sr alloys for cardiovascular bioabsorbable devices

ABSTRACT In this study, the mechanical and biocorrosion behavior of as-cast Zn-xCu-0.1Sr (x = 1, 2, and 3wt%) alloys for potential application was studied. The microstructure, mechanical properties, and in vitro degradation of Zn-xCu-0.1Sr alloys were investigated. The results show that as Cu content increased from 1.0 to 3.0wt%, the number of CuZn5 phases increased and the average grain size of CuZn5 phases increased from 6.96 μm to 10.92 μm. The 2wt% addition of Cu resulted in the best mechanical properties with 129.4 MPa in ultimate tensile strength and 108.4 MPa in yield strength. Furthermore, the higher corrosion rate was experienced in the alloys with higher Cu content after immersion. Zn-xCu-0.1Sr alloys all presented appropriate in vitro degradation rates in a basically uniform degradation mode. The strength, ductility and biocorrosion property exhibited by the Zn-2Cu-0.1Sr alloy compositions make it a promising candidate for cardiovascular stent applications.

Effect of Sr on hot deformation behavior and microstructure of Al-4.6Mg alloy

The hot deformation behaviors of Al-4.6Mg and Al-4.6Mg-0.2 Sr alloys at temperatures of 300–450 ℃ and strain rates of 0.001–1 s−1 were comparatively studied. Optical microscopy (OM), electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM) were used to study the effect of Sr on the microstructures of the alloys. The constitutive equations of Al-4.6Mg and Al-4.6Mg-0.2 Sr alloys were established. The apparent activation energies of the two alloys were 165.632 and 157.456 kJ/mol, respectively. The microscopic analysis showed that Sr had no significant effect on the grains of the as-cast Al-4.6Mg alloy, the precipitation phase changed, and the needle-like Al4Sr phase was formed. During isothermal compression (IC), both alloy samples consisted of slender grains and new quasi-equiaxed grains. Compared with the Al-4.6Mg alloy, the Al-4.6Mg-0.2 Sr alloy had a lower LnZ value, a smaller grain size, and more sufficient dynamic recovery (DRV); in addition, the grain growth of the Al-4.6Mg-0.2 Sr alloy was suppressed. The main textures of the Al-4.6Mg alloy were Goss and cubic textures, which were replaced by cubic and brass textures after adding Sr. During the IC of the Al-4.6Mg-0.2 Sr alloy, a nanoscale precipitated τ phase, which was uniformly distributed inside spherical grains, was formed.

Modeling of Microstructure and Mechanical Properties of Heat Treated ZE41-Ca-Sr Alloys for Integrated Computing Platform

The main objective of this study is to present a methodology to model the microstructure and mechanical properties of ZE41-xCa-ySr alloys for integrated optimization calculation of the heat treatment process of gearbox casting. Firstly, the models of microstructure and mechanical properties of ZE41-xCa-ySr alloys (0 ≤ x ≤ 2, 0 ≤ y ≤ 0.2) are developed using an artificial neural network (ANN) and multivariate regression. The dataset for ANN and regression models is generated by investigating the microstructures and mechanical properties of the ZE41-xCa-ySr alloys. The inputs for ANN and regression models are Ca and Sr contents, aging temperature and aging time. The outputs are grain size, ultimate tensile strength, elongation and microhardness. The optimal ANN model is obtained by testing the performance of different network architectures. In addition, multivariate regression models have been built based on the Least Squares method. Secondly, based on SiPESC software, an Integrated Computing Platform is constructed by combining the scripting language with the command line operation of simulation software, realizing the “process—microstructure—property” optimization calculation. Finally, based on the developed regression model, an Integrated Computing Platform batch called MATLAB achieves the heat treatment process optimization based on mechanical property prediction. The optimum aging temperature of the ZE41-0.17Ca-0.2Sr alloy is 322 °C, and the corresponding aging time is 11 h. Furthermore, the optimized results are validated by the ANN model, suggesting that ANN predicted results are in good agreement with optimized results. As a consequence, this work provides a new strategy for the research and development of Mg alloys, contributing to acceleration in the development of magnesium alloys.

Improved corrosion resistance and mechanical properties of biodegradable Mg–4Zn–xSr alloys: effects of heat treatment, Sr additions, and multi-directional forging

The effects of Sr additions, heat treatment (T4 and T6), and multi-directional forging on the microstructural evolution, mechanical properties and biodegradability of Mg–4Zn–xSr alloys were investigated. Corrosion behavior of the alloys was evaluated by the polarization and hydrogen evolution tests. Shear punch and hardness tests were employed to determine the mechanical properties. It was found that mechanical properties and corrosion resistance of the as-cast Mg–4Zn alloy increased by 0.3 wt% Sr addition. However, further increasing the Sr content not only did not improve the mechanical strength, but also had detrimental effects on the corrosion resistance, due to the increased size and volume fraction of the intermetallic particles. While T4 heat treatment decreased the corrosion current density of Mg–4Zn–0.3Sr alloy from 2.58 to 2.1 μA/cm2, it resulted in some mechanical softening. On the other hand, T6 heat treatment significantly improved mechanical strength of the Mg–4Zn–0.3Sr alloy by about 10 MPa, while its effect on corrosion resistance was minor. Multi-directionally forged Mg–4Zn–0.3Sr alloy also demonstrated improved mechanical and corrosion properties compared to the as-cast condition, which was mainly attributed to the smaller grain size as well as better distribution of the secondary phases.

A newly developed Mg-Zn-Gd-Mn-Sr alloy for degradable implant applications: Influence of extrusion temperature on microstructure, mechanical properties and in vitro corrosion behavior

The object of this study is to investigate the influence of extrusion temperature on the microstructure, mechanical properties and in vitro corrosion behavior of Mg–2Zn–1Gd–0.4Mn–0.1Sr (ZGMS) alloy. The results show that as–extruded ZMGS alloy mainly contains α–Mg and Mg3Zn3Gd2 (W) phases, and the W phase is uniformly distributed in the Mg matrix. With decreasing extrusion temperature, the grain size is refined, and numerous nano–sized W particles dynamically precipitate during extrusion process. The mechanical properties of as–extruded experimental alloy is significantly improved with decreased extrusion temperature.This is owing to the effects of grain boundary strengthening, precipitation strengthening and dislocation strengthening. The experimental alloy exhibits the lowest corrosion rate and relatively uniform corrosion after extrusion at 360 °C. The corrosion products layer are mainly composed of Ca10(PO4)6(OH)2, Ca3(PO4)2 Mg(OH)2 and MgHPO4. The as–extruded alloy owns excellent mechanical properties (yield strength of 206.3 MPa ultimate tensile strength of 261.1 MPa and elongation of 27.3%) and corrosion rate (0.17 mg/cm2/day) after extruded at 360 °C. The alloy presents tremendous potential in degradable implant applications. Additionally, the relationship between microstructure and corrosion behavior was systematically discussed.

Efficient alloy design of Sr-modified A356 alloys driven by computational thermodynamics and machine learning

• A reliable CALPHAD thermodynamic database of al-Si-Mg-Sr system was established. • The quantitative composition-microstructure-properties relation was constructed. • The optimal Sr additional amount in A356 alloys was designed as 0.005 wt.%. • The strengthening/toughening mechanisms of Sr-modified A356 alloys were analyzed. A356 alloys are widely used in industries due to their excellent comprehensive performance. Sr is usually added in A356 alloys to improve their mechanical properties. There have been various experimental reports on the optimal additional amount of Sr in A356 alloys, but their results are inevitably inconsistent. In this paper, a combination of computational thermodynamic and machine learning approaches was employed to determine the optimal Sr content in A356 alloys with the best mechanical properties. First, a self-consistent thermodynamic database of quaternary Al-Si-Mg-Sr system was established by means of the Calculation of PHAse Diagram technique supported by key experiments. Second, the fractions for solidified phase/structures of A356- x Sr alloys predicted by Scheil simulation, together with the measured mechanical properties were set as the input dataset in the machine learning model to train the relation of “composition-microstructure-properties”. The optimal addition of Sr in A356 alloy was designed as 0.005 wt.% and validated by key experiments. Furthermore, such a combinatorial approach can help to understand the strengthening/toughening mechanisms of Sr-modified A356 alloys. It is also anticipated that the present approach may provide a feasible means for efficient and accurate design of various casting alloys and understanding the alloy strengthening/toughening mechanisms.

Effect of Cooling Rate on Nano-Eutectic Formation in Laser Surface Remelted and Rare Earth Modified Hypereutectic Al-20Si Alloys

Laser Surface Remelting (LSR) was applied to arc-melted Al-20Si-0.2Sr, Al-20Si-0.2Ce, and Al-20Si hypereutectic alloys to refine microstructures. Experiments revealed that microstructures in the melt pool varied from fully eutectic to a mixture of Al dendrites and inter-dendritic eutectic. We calculated cooling rates using the Eagar-Tsai model and correlated cooling rates with characteristic microstructures, revealing that a cooling rate on the order of 104 K/s could lead to maximized fully eutectic microstructure morphology. Due to rapid solidification, the Si composition in the LSR eutectic was measured at 18.2 wt.%, higher than the equilibrium eutectic composition of 12.6 wt.%Si. Compared to Al-20Si, Ce addition had no significant effect on the volume fraction of the fully eutectic structure but refined Si fibers to approximately 30 nm in diameter. Sr addition did not further refine the diameter of eutectic Si fibers compared to Al-20Si but increased the volume fraction of the fully eutectic microstructure morphology. The refinement ratio (φ) of the Si fiber diameter from the bottom of the melt pool to the surface for the three alloys was similar, at around 28%. The established correlation between the cooling rate and the size and morphology of the microstructure within the melt pool will enable tailoring of the microstructure in laser-processed as well as deposited alloys for high strength and plasticity.

Effect of strontium on microstructure, mechanical, and biological responses of Mg–Al–Zn–Sr alloys

In the present study, Mg alloys were prepared with different strontium contents and investigated for applications as resorbable implants (screws, plates, stents etc.). Microstructural characterisation and phase analysis were performed by optical microscopy, scanning electron microscopy, X-ray diffraction, and transmission electron microscopy. Alloy with 0.5 wt-% strontium results in a microstructure with fine grains (179 ± 22 µm) and the highest second phase precipitates (area-fraction ∼1.55%). The immersion and electrochemical measurements were performed at different times in Hanks’ solution. The corrosion rate decreased with increasing strontium amount owing to precipitate barrier and protective corrosion products. In vitro biocompatibility test was carried out by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide assay. The cell viability decreases with an increase in strontium content owing to presumably higher fraction of the Mg17Sr2 phase.

In vivo comparison of the degradation and osteointegration properties of micro-arc oxidation-coated Mg-Sr and Mg-Ca alloy scaffolds.

Magnesium (Mg) alloy have biodegradation and mechanical properties that are similar to those of human bone, making it a promising candidate material for inclusion in implantable medical devices. The osteointegration effect of Mg alloy scaffolds with different corrosion rates were studied and evaluated in large bone defect models. Mg-Sr and Mg-Ca alloy scaffolds with a 20-μm Micro-arc oxidation (MAO) coating were used to repair critical bone defects for subsequent assessment of each alloy's degradation and osteointegration by X-ray, Micro-CT, fluorescence and histological examination. At 12 weeks post-implantation, each defect was found to be effectively reconstructed by either of the Mg alloys based on X-ray and Micro-CT images. The corrosion rate (CR) of each Mg alloy - as calculated based on micro-computed tomography information - demonstrated that the MAO coating could provide effective protection for only 4 weeks post-surgery. From weeks 8 to 12, the CR of the Mg-Ca alloy scaffold increased from 1.34±0.23mm/y to 1.57±0.16 mm/y. In contrast, the CR of the Mg-Sr alloy scaffold decreased from 0.58±0.14mm/y to 0.54±0.16mm/y. However, fluorescence and histological examination revealed more mature, closely and regularly arranged newborn osteocytes at the Mg-Ca scaffold-fracture interface e from weeks 8 to 12 after surgery. The Mg-Sr scaffold was more corrosion resistant and the Mg-Ca scaffold yielded a better overall repair, which indicates that the CR of magnesium alloys matches the rate of new bone formation and is the key to repair bone defects as a bone substitute.

Experimental research on machinability characteristics of Al-9Si alloy: Effect of Sr and Mg additives

In this study, the effects of strontium (Sr) and magnesium (Mg) elements in certain rates added to Al-9Si alloy manufactured using permanent mold casting technique on the structural, mechanical, and machinability properties of these alloys were investigated. While microstructural images of the alloys were obtained with an optical microscope, hardness, tensile strength, and elongation to fracture were determined by conventional methods. The resultant cutting force ( F) and average surface roughness ( Ra) were measured as experimental outputs in the turning process. It was observed that Al-9Si alloy comprised of α-Al, eutectic Al-Si, β, and primary Si phases. The addition of Sr to the Al-9Si alloy led to the formation of the Al4Sr phase and the transformation of the β phase into the δ phase. The addition of Mg to Al-9Si-0.1Sr alloy caused the δ phase to transform into the π phase. The hardness of the tested alloy increased significantly with the Mg addition. The yield strength and tensile strength of them increased with both Sr and Mg additions. On the other hand, elongation to fracture value of the Al-9Si alloy increased with Sr addition while it decreased with the Mg addition. The F and Ra values obtained from the Al-9Si alloy increased with Sr addition in the turning process while decreased with Mg addition. The results obtained from turning tests were discussed based on the mechanical properties of alloys.

Investigation of Structural and Mechanical Properties of Nanostructured TiMgSr Alloy for Biomedical applications

In this study, Nanostructured TiMgSr alloy is produced by cold Isostatic Pressing (CIP) followed by microwave sintering. The fabricated alloy results in the formation of solid binary solutions along with the elemental phases. The CIP compacted alloy was characterized using X-ray diffraction (XRD) and scanning electron microscopy (SEM) to investigate the phases and the morphology. The presence of intermetallic phases SrTiO3 and Mg17Sr2 along with elemental Ti, Mg, and Sr crystallites with a narrow peak during the sintering process is prevalent; however, the crystallite size was retained in the nanoscale regime around 58 nm. The developed titanium alloy exhibits a low Young's modulus and good strength. The young's modulus of Ti–Mg–Sr alloys was around 48.11 GPa, significantly closer to human cortical bone (10–30 GPa). Among so far developed Ti-based alloys, the CIP consolidated Ti-Mg-Sr alloy results in low young modulus and hardness. In the future, it may be used practically for biomedical applications.

The evolution of microstructure and mechanical properties of Zn-0.8Mg-0.2Sr alloy prepared by casting and extrusion

Zinc-based alloys containing elements well-tolerated by the organism (Mg, Ca, Sr) are considered as perspective biodegradable materials for an application like medical devices such as fixations of fractured bones or even stents. In the presented paper we characterize the relations between microstructure and mechanical properties of extruded Zn-0.8Mg-0.2 Sr alloy (wt%) depending on various parameters like extrusion temperature (150–300 °C) and ratio (11 or 25). Typical analysis including SEM with EBSD and mechanical tests indicate a strong dependence of obtained data on both extrusion temperature and ratio. Relatively wide range of elongation to fracture (2–22%) and anisotropy in compression yield strengths regarding loading direction (50–150 MPa) are explained by the huge effect of grain size, material texture and also the existence of dislocation substructures in materials extruded at elevated temperatures. Based on obtained results, appropriate extrusion conditions (200 °C, extrusion ratio 25) are suggested to reach the combination of superior mechanical properties 244 MPa, 324 MPa and 22% for tensile yield strength, ultimate tensile strength and elongation to fracture, respectively.

Effect of Sr on the microstructure and corrosion properties of the as-cast Mg–Zn–Zr alloy

Abstract The effect of Sr on the microstructure of Mg–Zn–Zr alloys was investigated by means of scanning electron microscopy, energy dispersive X-ray spectroscopy and X-ray diffraction. An immersion experiment and electrochemical experiment were designed to study the effect of Sr on the corrosion performance of the alloys. The results show that the addition of Sr promotes the formation of Mg17Sr2 phase in the alloy, and this stripe phase appears at the alloy grain boundaries. With the increase in Sr content, a network structure is formed at the grain boundary, creating a corrosion barrier to prevent further corrosion of the alloy. The study found that Mg-4Zn-0.4Zr-1.0Sr alloy has the best corrosion performance.

Microstructure selection map for rapidly solidified Al-rich Al–Sr alloys

Abstract The effect of rapid solidification on the microstructure of Al-5Sr, Al-10Sr and Al-23Sr (wt.%) alloys has been investigated using X-ray diffraction and transmission electron microscopy. The phases present in the melt-spun Al –Sr alloys are the equilibrium phases a-Al and tetragonal Al4Sr. The microstructure of the melt-spun Al –Sr alloys is quite different from that of the ingot-like alloys. Microstructure selection map is established for the rapidly solidified Al-rich Al –Sr alloys, in light of the microstructure together with the estimated cooling rates. The undercooling obtained through quenching at ≈ 9.5 × 105 K s–1 is sufficient for the Al-10Sr alloy but insufficient for the Al-23Sr alloy to completely suppress the formation of primary Al4Sr. Rapid solidification has a significant effect on the morphology of primary Al4Sr and the higher level of undercooling enhances the formation of the Al4Sr dendrites with 45° branches in the melt-spun Al-23Sr alloy.

Determination of Optimum Zn Content for Mg-0.5mn-0.5sr Alloy in Terms of Mechanical Properties and in Vitro Corrosion Resistance

Determination of Optimum Zn Content for Mg-0.5mn-0.5sr Alloy in Terms of Mechanical Properties and in Vitro Corrosion Resistance

Modeling heats of solution for CuNixM(1−x): M = Rh, Sr, and Ir alloys

So far, many research works have been carried out on the heats of solutions for binary alloy systems, but research studies on ternary heats of solutions are still scarce. The thermodynamic properties of the ternary CuNixM(1−x) system, where M = Rh, Sr, and Ir, were predicted using the concept of the thermodynamic properties of binary systems for the ternary system. The idea of predicting CuNixM(1−x) values was regarded as the calculation of the values of heats of solutions and Gibbs free energy for the ternary alloys. The embedded atom method formalism was used to calculate the parameters for the heats of solutions of binary alloys in reasonable compliance with the available experiment and was extended to the prediction of the thermodynamic properties of ternary alloys. The calculated heats of solutions of the ternary systems Cu–Ni–Rh, Cu–Ni–Sr, and Cu–Ni–Ir are −0.814, 16.840, and −1.504 eV, respectively. It was observed that the heat of solution decreases as the value of x increases with Rh and Sr, while the heat of solution increases as x increases for Ir. The stability order is Cu–Ni–Ir, Cu–Ni–Rh, and Cu–Ni–Sr. The liquidus temperature TL at various values of x = 0.00, 0.25, 0.50, 0.75, and 1.00 for the ternary alloys is presented.

Biodegradable Zn–Sr alloys with enhanced mechanical and biocompatibility for biomedical applications

Zinc (Zn) is a new generation of biodegradable metal as temporary biomedical implants with a promising degradation rate. However, its clinical applications have been limited because of the insufficient mechanical properties. Considering the degradation property and biocompatibility, we proposed Zn–Sr alloys after extrusion treatments to simultaneously improve the mechanical strength and ductility. The in vitro and in vivo degradation and biocompatibility were also evaluated using electrochemical and immersion corrosion tests, various cell and bacterial models, together with subcutaneous and femoral implantations in rats. Results showed that the extruded Zn-0.7Sr alloys exhibited two times higher mechanical strengths (∼120 ​MPa) and better ductility (∼10%) than the pure Zn counterparts. The Zn–Sr alloys provided enhanced in vitro and in vivo biocompatibility along with promising antibacterial properties.

Synthesis and characterization of mechanically alloyed nanostructured ternary titanium based alloy for bio-medical applications

This research article interprets the findings of experimental investigation on synthesis and characterization of a Ti alloy powder by using a high-energetic ball milling (HEBM) process. The work focuses on the synthesis of alloy powder with 70:10:20 (atomic %) of Ti, Mg, and Sr powders by process of mechanical alloying thereby decreasing the grain size of the particles to a Nanoscale regime from a micron scale. Tungsten carbide milling media was selected to synthesize alloy due to its higher density compared to elemental powder mixtures. Furthermore, the production of ternary Ti alloy with Mg and Sr additions could enhance the structural properties with density reduction which are quite suitable for biomedical applications. Mechanically alloyed powders are then characterized by X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM) with EDS, and High-Resolution Transmission electron microscope (TEM) to investigate the structural, phase transformation, compositional, morphology, and topography. XRD results revealed that the crystallite size decreased to 32.07 nm, and the formation of nonequilibrium intermetallic phases such as MgTiO3, Mg23Sr6, Mg2Sr, and Sr3Ti2O7, with an increase in ball-milling duration. However, the absence of sharp peaks indicates partial amorphization of crystalline powders as the milling progresses. SEM analysis at 30 h of milling time, the powder particles fractures, disintegrate to finer size and agglomerates by the process of welding. TEM revealed nano crystallites and amorphous structures, whereas the selected area diffraction pattern shows a halo amorphous image as well as crystalline brilliant rings, indicating a shift from crystalline to the partial amorphous structure during the ball milling process. The developed novel Ti–Mg–Sr alloy (wherein, Titanium for longer life span, Sr and Mg improve mineral density and bone strength) could be useful for biomedical application.

Effect of extrusion on the microstructure and corrosion behavior of Mg-Zn-Mn-(0, 1.5)Sr alloys in Hank’s solution

The microstructure, corrosion behavior, and cytocompatibility of as-cast and extruded Mg-Zn-Mn-(0, 1.5)Sr alloys in Hank’s solution are investigated. Grain refinement and preferred texture are confirmed after extrusion, while increase in dislocation density and fragmentation of Mg17Sr2 phases are the distinct features of Sr-free and Sr-containing alloys, respectively. Corrosion rate of Sr-free alloy is significantly accelerated by extrusion, while alloyed Sr eliminates this deterioration process. Alloying of Sr decreases the corrosion rate and enhances the cytocompatibility of the extruded Mg-Zn-Mn alloy without affecting the corrosion penetration depth, demonstrating the superiority of Sr alloying for the extruded magnesium alloy as implant materials.

Theoretical investigations of structural, mechanical, electronic, and thermodynamic properties of BaNYO (Y = Mg, Ca, and Sr) alloys

Theoretical investigations of structural, mechanical, electronic, and thermodynamic properties of BaNYO (Y = Mg, Ca, and Sr) alloys