A High-Strength and Biodegradable Zn–Mg Alloy with Refined Ternary Eutectic Structure Processed by ECAP

In this study, the microstructure, mechanical properties and corrosion behaviors of a Zn–1.6 Mg(wt%) alloy during multipass rotary die equal channel angle pressing(RD-ECAP) processing at 150 °C were systematically investigated. The results indicated that a Zn + Mg_2 Zn_(11) + MgZn_2 ternary eutectic structure was formed in as-cast Zn–Mg alloy. After ECAP, the primary Zn matrix turned to fine dynamic recrystallization(DRX) grains, and the network-shaped eutectic structure was crushed into fine particles and blended with DRX grains. Owing to the refined microstructure, dispersed eutectic structure and dynamically precipitated precipitates, the 8 p-ECAP alloy possessed the optimal mechanical properties with ultimate tensile strength of 474 MPa and elongation of 7%. Moreover, the electrochemical results showed that the ECAP alloys exhibited similar corrosion rates with that of as-cast alloys in simulated body fluid, which suggests that a high-strength Zn–Mg alloy was successfully developed without sacrifice of the corrosion resistance.     

Effect of Microstructure on Corrosion Behavior of Mg–Sr Alloy in Hank's Solution

Mg–Sr alloy has been studied as a potential biodegradable material with excellent bioactivity to promote the bone formation. However, its degradation behavior needs to be well controlled to avoid the negative effect, which is important for future application. Therefore in this study, the microstructure and its effect on corrosion behavior of an Mg–1.5 Sr alloy were investigated. The microstructures of the alloy under different processing procedures were characterized by both optical and scanning electron microscopes. The corrosion performance was studied in Hank's solution using immersion,potentiodynamic polarization and electrochemical impedance spectroscopy(EIS) tests. The results showed that the grain size and the amount and distribution of b-Mg_(17)Sr_2 had obvious effects on the corrosion behavior of Mg–Sr alloy. The smaller the grain size was, the more the protective surface layer formed on Mg–Sr alloy, and the higher the corrosion resistance was. For the as-cast Mg–Sr alloy, the network-like second phases precipitated along the grain boundaries could not hinder the corrosion due to their own corrosion cracking accelerating the intergranular corrosion. However, the refinement of second phases increased the corrosion resistance of the as-extruded alloy. After solution treatment at 450 °C for 5 h, the grains in the alloy did not grow much and b-Mg_(17)Sr_2 phases homogenously distributed in the alloy, resulting in the increase in corrosion resistance. However, after aging treatment, large amount of precipitated second phases increased the galvanic corrosion of the alloy, accelerating the development of corrosion.     

Precipitation behavior of 14H-LPSO structure in Mg–12Gd–2Er–1Zn–0.6Zr Alloy

The microstructures of as-cast and as-solution Mg–12Gd–2Er–1Zn–0.6Zr alloys were investigated by optical microscopy(OM), scanning electron microscopy(SEM), transmission electron microscopy(TEM), highresolution transmission electron microscopy(HRTEM)X-ray diffraction(XRD) and selected-area electron diffraction(SAED) in the present investigation. The results show that the primary eutectic phase Mg_5(Gd, Er, Zn) and some flocculent features are found in the as-cast alloy; the SAED pattern indicates that these flocculent features are the dense areas of stacking faults. The 14H-LPSO structure precipitates in the temperature range of 673–793 K, and the volume fraction of 14H-LPSO structure increases with the extension of heating time; however, there is no precipitation of 14H-LPSO structure when the temperature reaches up to 803 K. In addition, the Mg_5(Gd, Er, Zn) phase dissolves gradually along with the precipitation of 14H-LPSO structure.     

Effect of Different Scale Precipitates on Corrosion Behavior of Mg–10Gd–3Y–0.4Zr Alloy

A large amount of directional and willow-like β' phase was precipitated in Mg-10 Gd-3 Y-0.4 Zr(GW103 K) alloy after solution treatment and subsequently aged treatment(T6). In order to explore the effect of the precipitates on the corrosion behavior of the GW103 K alloy, the alloy was subjected to solution treatment(T4) at 773 K for 4 h at first, subsequently aged at 498 K for 193 h(T6). The microstructure evolution of the GW103 K alloy after this treatment was investigated by scanning electron microscopy and transmission electron microscopy. The high-angle annular detector dark-field scanning transmission electron microscopy was used to observe the typical corrosion morphologies of the nanoscale precipitation phases(β') in the T6-treated alloy. The corrosion rate was measured by potentiodynamic polarization test. Combining with the potential measurement results by scanning Kelvin probe force microscopy, the effects of the skeleton-like Mg_(24)(Gd,Y)_5 andf precipitates on the corrosion behavior of GW103 K alloy were explored. The results showed that the corrosion rate of the GW103 K alloy in different conditions was ranked as: as-cast alloy T4-treated alloy T6-treated alloy,attributing to the fact that the relative potential differences of skeleton-like Mg_(24)(Gd,Y)_5 were lower than those of the matrix, therefore Mg24(Gd, Y)5 phase formed micro-galvanic coupling with the matrix and corrosion dissolution occurred.The nanoscale β' precipitates in T6-treated alloy can retard the cathodic process.     

Microstructure and corrosion behavior of Zr–1.0Cr–0.4Fe–xMo alloys

Possibility of using Mo as an alloying element in Zr-based alloys was attractive in terms of microstructure refinement and mechanical properties strengthening. In this research, Zr–1.0Cr–0.4Fe–xMo(0, 0.2, 0.4, and 0.6) alloys with different Mo contents were prepared by vacuum arcmelting method, the microstructure and the corrosion resistance of these alloys were investigated. Addition of Mo has a refinement effect on the microstructure; with the increase of Mo content, the a-laths in the as-cast samples and the grain size in the annealed samples decrease. Zr–1.0Cr–0.4Fe–xMo alloys have large numbers of fine second-phase particles(SPPs) in the matrix, the area fraction of the SPPs is more than 10 %. With the increase of Mo content, the population density of the SPPs increases significantly, while the average diameter of the SPPs decreases. Mo addition also affects the texture; the intensity of basal pole texture aligning normal direction decreases with the increase of Mo content in the alloys.Compared with Zr-4 and Zr–1Nb, Zr–1.0Cr–0.4Fe–xMo alloys have excellent corrosion resistance in 500 °C/10.3 MPa steam. The corrosion rates of Mo-containing alloys are higher than that of Mo-free alloy, which is mainly attributed to the solute Mo atoms in the Zr matrix.Change of the SPPs features due to the increase of Mo content alleviates the degradation of corrosion resistance in some degree, but it is not the dominant factor.     

Biodegradation Behavior of Coated As-Extruded Mg–Sr Alloy in Simulated Body Fluid

As-extruded Mg–Sr alloy, a kind of promising biodegradable biomedical material, was coated using micro-arc oxidation and also using a phosphate conversion coating. The corrosion behaviors were investigated using Hanks' solution. The corrosion of the as-extruded Mg–Sr alloy became more serious with increasing immersion time; that is, the corrosion pits became more numerous, larger and deeper. The micro-arc oxidation coating and the phosphate conversion coating were effective in improving the corrosion resistance of the as-extruded Mg–Sr alloy. The micro-arc oxidation coating was much more effective. Moreover, the as-extruded Mg–Sr alloy and the coated as-extruded Mg–Sr alloy exhibited lower corrosion rates than the as-cast Mg–Sr alloy and the corresponding coated as-cast Mg–Sr alloy, indicating that the corrosion properties of the coated samples are dependent on their substrates. The finer microstructure of the substrate of the as-extruded condition corroded much slower. The corrosion resistance of the coated Mg–Sr alloy depended on the coating itself and on the microstructure of the substrate.     

Microstructure,mechanical and biodegradable properties of a Mg–2Zn–1Gd–0.5Zr alloy with different solution treatments

Solution treatment is a useful way to improve the degradation resistance of Mg alloys.In this work,effects of solution treatment temperature on mechanical and biodegradable properties of an extruded Mg–2Zn–1Gd–0.5Zr alloy were studied.Microstructure analysis,tensile test, three-point bending test, immersion test and electrochemical test were performed.The results showed that increasing solution temperature decreases the mechanical properties of the alloy.However, three-point bending test revealed that the solution-treated alloy at 510 ℃ could maintain 95% of its maximum bending force(F_(max)) during the 28-day immersion period.After treatment at 510 ℃ for 5 h, all the second phases were dissolved into the alloy, the galvanic corrosion was inhibited, and the alloy exhibited good corrosion resistance with a corrosion rate of 0.35 mm·year~(-1) in Hank's solution.     

Mechanical properties and energy absorption of extruded Mg–2.0Zn–0.3Zr alloy with Y addition

The effects of the rare earth element Y addition on mechanical properties and energy absorption of a low Zn content Mg–Zn–Zr system alloy and the deformation temperature of optimized alloy were investigated by room tensile test, optical microscopy(OM), X-ray diffraction(XRD), scanning electron microscopy(SEM), and transmission electron microscope(TEM). The results show that,after homogenization at 420 °C for 12 h for the as-cast alloys, Mg Zn phase forms, which decreases the strength of Mg–2.0Zn–0.3Zr alloy with Y content of 0.9 wt%. The tensile strength and elongation of the alloy with a Y addition of 5.8 wt% reach the max value(281 ± 2) MPa and(30.1 ± 0.7) %, respectively; the strength and elongation of Mg–2.0Zn–0.3Zr–0.9Y alloy at the optimized extrusion temperature of 330 °C reach(321 ± 1) MPa and(21.9 ± 0.7) %, respectively. The energy absorption increases with the increase of Y content, the max value reached 0.79 MJ m-3with Y content of 5.8 wt%, and the energy absorption of Mg–2.0Zn–0.3Zr–0.9Y alloy at the optimized extrusion temperature of 330 °C reaches0.75 MJ m-3.     

Corrosion properties of plastically deformed AZ80 magnesium alloy

AZ80 magnesium alloys were deformed at 200,250,300,350 and 400℃ with different deformation degree of 50%,75%, 83%,87%and 90%,respectively.The corrosion properties of different deformed AZ80 samples were studied by galvanic test in 3.5%NaCl solution.The results show that plastic deformation could improve the corrosion resistance of AZ80 alloy;and the corrosion rate of AZ80 deformed at 250℃ with the deformation degree of 83%was the lowest,which was 33%of the as-cast AZ80 alloy.Further studies of the microstructure show that the refined grain size and continuously distribution ofβphase around the grain boundary did have a positive effect on the improvement of corrosion resistance of AZ80 alloys.For AZ80 alloys,the smaller the grain size is,the more homogeneous the structure is,and the better the corrosion resistance is.     

Achieving higher strength in Cu–Ag–Zr alloy by warm/hot rolling

High-strength Cu–3Ag–0.5Zr alloy plates were produced by multi-pass rolling in the temperature range of500–800 °C. An increase in strength was observed by rolling in the aforementioned range without significant loss in ductility. All the rolled samples show higher strength than solution-treated and aged samples. The maximum strength was observed for plates rolled at 500 °C with a yield strength and ultimate tensile strength of 311 and385 MPa, respectively, and retaining a ductility of 23 %.Transmission electron microscopy(TEM) studies showed uniform distribution of fine silver precipitates and high dislocation density in the rolled samples. Nevertheless, the size of precipitates and dislocation density varied with the rolling temperature. The superior strength achieved in the rolled samples is attributed to grain refinement, dislocation strengthening, and precipitation hardening. This method can be employed to produce high-strength plates of precipitation hardenable copper alloys.     

具有长周期结构的Mg–Gd–Zn–Zr合金的微结构和摩擦学行为

利用传统的熔铸法制备Mg-14.28Gd-2.44Zn-0.54Zr合金,研究铸态和固溶态合金的微结构。利用销-盘装置研究铸态和固溶态合金的室温润滑滑动摩擦磨损行为研究。在外载荷为40 N,滑动速度为30-300 mm/s以及滑行路程为5000 m情况下,测量磨损率和摩擦因数。研究结果表明：铸态合金主要由α-Mg固溶体、分布在基体内的层片状的14H型长周期结构（LPSO）和β-[（Mg,Zn）3Gd]相组成。经过温度为773 K固溶处理35 h后,大量的β相转变成具有14H型X相LPSO结构。由于固溶处理后大量β相转变为热稳定的韧性X-Mg12Gd Zn长周期结构相,固溶合金呈现较低的抗磨损能力。     

固溶处理对铸造AM50镁合金腐蚀力学性能的影响

研究了铸造AM50镁合金固溶处理后的组织及腐蚀力学性能的变化规律。结果表明,固溶处理后,由于大量Al固溶进α-Mg中,AM50镁合金相组成主要为α-Mg固溶体。此外,固溶处理没有改变AM50镁合金的断裂机制,仍为准解理断裂。受最大蚀坑深度和固溶强化理论影响,在腐蚀时间为24 h前,镁合金固溶处理后的腐蚀剩余强度高于铸态;而在72 h至336 h之间,固溶处理后的镁合金剩余强度低于铸态;在432 h时,固溶处理后的合金剩余强度重新高于铸态合金。铸态和固溶处理后AM50镁合金的腐蚀速率均呈现出先大后小的规律,这种现象主要由镁合金在NaCl溶液中的腐蚀原理决定的。     

T6处理工艺对Mg-Y-Cu-Zr合金显微组织和耐腐蚀性能的影响

为研究T6热处理工艺对Mg-6.6Y-2.6Cu-1.2Zr镁合金组织和耐腐蚀性能的影响,对合金进行了不同工艺的固溶处理和相同工艺的时效处理。固溶处理工艺为420℃、440℃和460℃保温12h水冷,时效处理工艺为200℃×12h。采用光学显微镜和扫描电镜观察合金的显微组织,通过电化学法测试合金的耐蚀性能。结果表明:随着固溶温度的升高,合金中β相数量减少,且其形貌从不规则形状转变为条状;LPSO结构的体积分数先增多后减少;合金的腐蚀速率先增大随后显著降低。经460℃×12h水冷随后200℃×12h时效处理的Mg-6.6Y-2.6Cu-1.2Zr合金的耐蚀性能显著提高,为铸态合金的4.6倍,表明合适的T6处理工艺可有效提高Mg-6.6Y-2.6Cu-1.2Zr镁合金的耐蚀性能。     

Effects of Solution and Aging Treatments on Corrosion Resistance of As-cast 60NiTi Alloy

60NiTi alloy has become a competitive candidate for bearing applications due to its shape memory effect, superelasticity, high strength, hardness, excellent abrasion resistance and corrosion resistance, etc. However, the relationship between its corrosion resistance and heat treatment is not clearly understood. Therefore, we used OM, XRD, SEM and EDS to study the evolution of microstructure in as-cast, solution-treated and aged 60NiTi alloy. Besides, the potentiodynamic polarization and salt spray test were used to compare corrosion resistance of 60NiTi alloy and 316 stainless steel and to study the effect of microstructures on corrosion resistance of 60NiTi alloy. The results show that the corrosion resistance of as-cast 60NiTi alloy is comparable to that of 316 stainless steel, but the corrosion resistance of solution-treated and aged 60NiTi alloys is much superior. The significantly reduced Ni₃Ti phase after the solution and aging treatments is responsible for the remarkable improvement in the corrosion resistance of as-cast 60NiTi alloy.     

Mg-6Gd-3Y-2Zn-0.5Zr镁合金的组织和性能

设计了新型Mg-6Gd-3Y-2Zn-0.5Zr镁合金,并用光学显微镜、扫描电镜及拉伸试验机对合金铸态、均匀化态及挤压态的显微组织特征和力学性能进行了研究。结果表明,铸态Mg-6Gd-3Y-2Zn-0.5Zr合金组织主要由α-Mg基体和沿晶界分布的块状长周期堆垛有序结构相组成,均匀化处理(450℃×16h)促使细小层片状的长周期堆垛有序结构相由晶界向晶内生长。挤压态Mg-6Gd-3Y-2Zn-0.5Zr合金在200℃下时效处理,无明显时效硬化现象,但挤压态合金具有优良的强韧性能,室温抗拉强度、屈服强度和伸长率分别为335MPa、276MPa和17%。     

Controlling Corrosion Resistance of a Biodegradable Mg–Y–Zn Alloy with LPSO Phases via Multi-pass ECAP Process

Mg-RE(rear earth) alloys with long period stacking(LPSO) structures have great potential in biomedical applications. The present work focused on the microstructure and corrosion behaviors of Mg 98.5 Y_1 Zn_(0.5) alloys with 18 R LPSO structure after equal channel angular pressing(ECAP). The results showed that the ECAP process changed the grain size and the distribution of LPSO particles thus controlled the total corrosion rates of Mg 98.5 Y_1 Zn_(0.5) alloys. During the ECAP process from 0 p to 12 p, the grain size reduced from 160–180 μm(as-cast) to 6–8 μm(12 p). The LPSO structures became kinked(4 p), then started to be broken into smaller pieces(8 p), and at last comminuted to fine particles and redistributed uniformly inside the matrix(12 p). The improvement in the corrosion resistance for ECAP samples was obtained from 0 p to 8 p, with the corrosion rate reduced from 3.24 mm/year(0 p) to 2.35 mm/year(8 p) in simulated body fluid, and the 12 p ECAP alloy exhibited the highest corrosion rate of 4.54 mm/year.     

Effect of Zn Addition on the Microstructure and Mechanical Properties of Cast Mg-10Gd-3.5Er-xZn-0.5Zr Alloys

In this work, the effects of Zn content (0-2 wt%) on microstructural evolution and mechanical properties of cast Mg-10Gd-3.5Er-0.5Zr alloys are studied. The results show that the as-cast Mg-10Gd-3.5Er-xZn-0.5Zr alloys are mainly composed of Mg matrix and secondary (Mg, Zn)₃(Gd, Er) phases distributed along grain boundaries. With the increase in Zn content, the volume fraction of secondary (Mg, Zn)₃(Gd, Er) phases increases and the grains get refined. In the process of solid solution treatment, Zn addition can lead to the formation of long-period stacking ordered (LPSO) structures and the volume fraction of LPSO structures increases with Zn content. In addition, the Zn addition can reduce the vacancy formation energy and accelerate the diffusion rate of RE elements in Mg matrix. Because of the comprehensive effect of secondary phases and the accelerated diffusion rate, the base alloy and 2Zn alloy have less grain growth after solid solution treatment than that of the 0.5Zn alloy and 1Zn alloy. The precipitation process is also accelerated by enhanced diffusion rate. At room temperature (RT), the strengthening effect of β^'+ β₁ precipitates is more effective than that of LPSO structures, so the peak-aged 0.5Zn alloy exhibits the most excellent mechanical performance at RT, with yield strength of 219 MPa, ultimate tensile strength 296 MPa and elongation of 6.4%. While LPSO structures have stronger strengthening effect at elevated temperature than that of β^'+ β₁ precipitates, so the 1Zn alloy and 2Zn alloy have more stable mechanical performance than that of the base alloy and 0.5Zn alloy with the increase in tensile temperature.     

Mg-3Ce-1.2Mn-0.9Sc和Mg-3Ce-1.2Mn-1Zn镁合金铸态组织和力学性能的比较(英文)

比较研究了Mg-3Ce-1.2Mn-0.9Sc和Mg-3Ce-1.2Mn-1Zn镁合金的铸态组织和力学性能。结果表明:含Sc合金主要由α-Mg、Mg12Ce和Mn2Sc相组成,而含Zn合金则主要由α-Mg和Mg12Ce相组成。然而,含Sc和含Zn铸态合金中Mg12Ce相的形貌是不同的。含Sc合金中的Mg12Ce相主要呈颗粒状,而含Zn合金中的Mg12Ce相则主要呈连续和/或准连续的网状。同时,含Sc合金的晶粒较含Zn合金的相对较为细小。此外,虽然含Sc合金和Zn合金在室温和300°C下具有相似的抗拉性能,但含Sc合金在300°C和30MPa下持续100h后的抗蠕变性能较Zn合金的好。     

Effect of Solution Treatment on the Microstructure and Mechanical Properties of Sand-Cast Mg–9Gd–4Y–0.5Zr Alloy

Sand-cast Mg–9Gd–4Y–0.5 Zr(wt%) alloy was solution-treated at 500–565 ℃ in the time range of 0.5–30 h in air or vacuum to investigate its microstructure evolution and mechanical properties. The results showed that solution treatment temperature had a significant influence on the dissolving rate of eutectic phase and grain growth. Taken both of them into consideration, 510–520 ℃ was considered to be the optimum solution treatment temperature range for this alloy.It should be noted that the trace(0.4–0.9 vol%) and insoluble cuboid-shaped phase precipitated during solution treatment was identified to be YH2, of which the hydrogen was thought to come from both the melting and solution heating process.In addition, the 3D morphology and dissolving process of Mg24(Gd,Y)5 eutectic phases in the as-cast alloy were also discussed via in-situ observation under X-ray tomography.     

热挤压对铸态Mg-1Zn-0.3Zr-1Y-2Sn镁合金组织和性能的影响（英文）

通过光学显微镜(OM)、扫描电镜(SEM)、浸泡实验、析氢实验、电化学试验、拉伸试验等方法,研究了不同挤压温度(340、360、380、400℃)下,热挤压对铸态Mg-1Zn-0.3Zr-1Y-2Sn合金组织和性能的影响。结果表明:热挤压后,合金的第二相沿挤压方向破碎成颗粒,微观组织中存在动态再结晶和变形晶粒。随着挤压温度的升高,第二相的含量变化较小,动态再结晶晶粒尺寸逐渐增大。热挤压后,合金的力学性能得到改善,但其耐腐蚀性最终减弱。热挤压处理可以在腐蚀的早期阶段提高合金的耐腐蚀性能,但随着腐蚀的进行,在后期合金的耐蚀性能会降低。当热挤压温度为360℃时,合金具有较好的力学性能和耐腐蚀性能。