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.     

Microstructures and mechanical properties of homogenization and isothermal aging Mg–Gd–Er–Zn–Zr alloy

The effects of homogenization and isothermal aging treatment on the mechanical properties of Mg–12Gd–2Er–1Zn–0.6Zr(wt%) alloy were investigated. The precipitated long-period stacking order(LPSO) structure and the aging precipitation sequence of the conditioned alloys were observed and analyzed, respectively. The results indicate that the 14H-LPSO structure occurs after the homogenization treatment and the b0 phase forms after the isothermal aging process. These two independent processes could be controlled by the precipitation temperature range. The significant increase in the elongation of the as-cast alloy after homogenization treatment is attributed to the disappearance of the coarse primary Mg5(Gd, Er, Zn) phase and the presence of the 14H-LPSO structure. The precipitation sequence of the investigated alloy is a-Mg(SSS)/b00(D019)/b0(cbco)/b.Furthermore, the yield tensile strength(YTS) and ultimate tensile strength(UTS) values of the isothermal aging alloy have a great improvement, which could be attributed to the high density of the precipitated b0 phase.     

Development of High Strength and Toughness Non-Heated Al–Mg–Si Alloys for High-Pressure Die-Casting

Based on the 3 factors and 3 levels orthogonal experiment method, compositional effects of Mg, Si, and Ti addition on the microstructures, tensile properties, and fracture behaviors of the high-pressure die-casting Al-x Mg-y Si-z Ti alloys have been investigated. The analysis of variance shows that both Mg and Si apparently infl uence the tensile properties of the alloys, while Ti does not. The tensile mechanical properties are comprehensively infl uenced by the amount of eutectic phase(α-Al + Mg_2Si), the average grain size, and the content of Mg dissolved into α-Al matrix. The optimized alloy is Al-7.49 Mg-3.08 Si-0.01 Ti(wt%), which exhibits tensile yield strength of 219 MPa, ultimate tensile strength of 401 MPa, and elongation of 10.5%. Furthermore, contour maps, showing the relationship among compositions, microstructure characteristics, and the tensile properties are constructed, which provide guidelines for developing high strength and toughness Al–Mg–Si–Ti alloys for high-pressure die-casting.     

Microstructures and Mechanical Properties of Mg–xAl–1Sn–0.3Mn( x = 1, 3, 5) Alloy Sheets

The influence of Al alloying on the microstructures and the mechanical properties of Mg–x Al–1 Sn–0.3 Mn alloy sheets was investigated. The microstructure of Mg– x Al–1 Sn–0.3 Mn consisted of α-Mg and Mg 17 Al 12 precipitates. Alloying with Al increased the amount of Mg_(17)Al_(12) and the average grain size. Uniaxial tensile tests were carried out along the extrusion direction(ED), the transverse direction(TD) and 45° toward the ED. Mg–5 Al–1 Sn–0.3 Mn alloy sheet exhibited the best combination of mechanical properties along the ED: a yield strength of 142 MPa, an ultimate tensile strength of 282 MPa and an elongation of 23%. The good performance of Mg–5 Al–1 Sn–0.3 Mn sheet was mainly attributed to the large quantity of Mg_(17)Al_(12) precipitates and a weak basal texture. Annealing caused static dynamic recrystallization, refined the grain size and enhanced the mechanical properties: yield strength of 186 MPa, ultimate tensile strength of 304 MPa, elongation of 21% along ED. Both strength and ductility were enhanced by Al alloying.     

Microstructure and mechanical properties of Mg–Zn–(Nd)–Zr alloys with different extrusion processes

The effect of Nd addition and the in?uence of extrusion processes on the microstructure and mechanical properties of Mg–6Zn–0.5Zr(ZK60) and Mg–6Zn–1.5Nd–0.5Zr(ZKNd602) alloys were investigated. Nd element can obviously re?ne the microstructure of both as-cast and asextruded Mg–Zn–Nd–Zr alloy. All of the extruded alloys exhibit a bimodal grain structure composed of equiaxed?ne recrystallized(DRXed) grains and elongated coarse un DRXed grains. It is necessary to achieve high strength,particularly the yield strength, for ZKNd602 alloy, when it is extruded with a lower extrusion temperature, a suitable extrusion ratio and a relatively lower extrusion ram speed. In this study, the ultimate tensile strength(UTS),yield strength(YS) and elongation(El) of the extruded ZKNd602 alloy were 421 MPa, 402 MPa and 6.7 %,respectively, with extrusion temperature of 290 °C, extrusion ratio of 18:1 and a ram speed of approximate0.4 mm·s~(-1). Meanwhile, the extrusion process has obvious effects on the room-temperature properties but weak effects on the high-temperature properties.     

Obtaining Ultra-High Strength and Ductility in a Mg–Gd–Er–Zn–Zr Alloy via Extrusion,Pre-deformation and Two-Stage Aging

The Mg–12Gd–1Er–1Zn–0.9 Zr(wt%) alloy with ultra-high strength and ductility was developed via hot extrusion combined with pre-deformation and two-stage aging treatment.The age-hardening behavior and microstructure evolution were investigated.Pre-deformation introduced a large number of dislocations,resulting in strain hardening and higher precipitation strengthening in the subsequent two-stage aging.As a result,the alloy showed a superior strength–ductility balance with a yield strength of 506 MPa,an ultimate tensile strength of 549 MPa and an elongation of 8.2% at room temperature.The finer and denser β' precipitates significantly enhanced the strength,and the bimodal structure,small β-Mg_5RE phase as well as dense γ' precipitates ensured the good ductility of the alloy.It is suggested that the combination of pre-deformation and two-stage aging treatment is an eff ective method to further improve the mechanical properties of wrought Mg alloys.     

A High-Ductility Mg–Zn–Ca Magnesium Alloy

A new kind of Mg–2 Zn–0.6 Ca(wt%) alloy was fabricated by casting and hot extrusion as a high-ductility structural material. The extruded alloy exhibits a superior elongation of ～30%, yield strength of 130 MPa and ultimate tensile strength of 280 MPa along the extrusion direction at room temperature. Microstructure, texture and tensile properties of the extruded alloy were investigated in details. The remarkable improvement of ductility is ascribed to the weakened basal texture, refined grains and a small number of second phase in the alloy.     

Enhancing Mechanical Properties of Mg–6Zn Alloy by Deformation-Induced Nanoprecipitation

We presented the solution of deformation-induced precipitation after homogenization to enhance the mechanical properties of Mg–6 Zn alloys. The results show that the improved strategy exhibits more effective strengthening role than grain refinement methods based on low-temperature severe plastic deformation under the same strain. The low-temperature deformation with larger extrusion ratio results in massive nano-sized precipitates and excellent mechanical properties with the yield strength of 355 MPa and the ultimate tensile strength of 405 MPa. The increased mechanical properties are strong and tough enough to resist the stress and not be worn away when the alloy nail penetrates through the pig thigh bone, potentially extending more orthopedic surgery applications for Mg–Zn alloys.     

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.     

Hot corrosion behavior and mechanical properties degradation of a Ni–Cr–W-based superalloy

The effect of molten salts on the mechanical properties of a Ni–20Cr–18W(wt%)-based superalloy was investigated in this work. The hot corrosion characteristics and the microstructural evolution during the hot corrosion process were analyzed. The corrosion scale forms on the surface of the substrate, and its thickness increases gradually during the process. The element of S invades the substrate. The corrosion products mainly include Ni O,Ni_3S_2 and Cr_2O_3. The hot corrosion in molten salt makes the specimens rough and flawed. The serration grain boundaries are observed in the hot corroded specimens.The tensile strength and elongation of the original alloy are~1023 MPa and ~15 %, respectively. After corroded for5 h, the tensile strength and elongation of the specimen decrease to ~771 MPa and ~7 % and diminish to~814 MPa and ~9 % for the specimen corroded for 10 h.The hot corrosion process deteriorates the mechanical properties of the alloys. And the tensile strength and elongation of the specimen corroded for 20 h sharply decrease to ~539 MPa and ~3 %, respectively. The nonmonotonic variation of the mechanical properties of the specimen occurs for the specimens corroded for 10 h,which is related to the competition between the depredation of the molten salts and the strengthening process by carbides and the serrated grain boundaries.     

Al和Li含量不同的时效态Mg-Gd-Zn-Zr-Ag合金的组织和力学性能

研究了铝和锂元素含量不同的Mg-12Gd-1Zn-0.5Zr-0.5Ag(质量分数,%)合金经T6热处理后的组织演变和力学性能。结果表明,T6热处理后,有新的Mg3Gd颗粒从Mg-12Gd-1Zn-0.5Zr-0.5Ag合金中析出,且Mg-12Gd-4Al-3Li-1Zn-0.5Zr-0.5Ag和Mg-12Gd-6Al-5Li-1Zn-0.5Zr-0.5Ag合金中的大多数Al2Li3相变得更细小,分布更均匀。时效态Mg-12Gd-4Al-3Li-1Zn-0.5Zr-0.5Ag和Mg-12Gd-6Al-5Li-1Zn-0.5Zr-0.5Ag合金中的晶粒尺寸和c/a比值相比时效态Mg-12Gd-1Zn-0.5Zr-0.5Ag合金有显著的减小,这有利于提高抗拉强度和塑性。时效态Mg-12Gd-6Al-5Li-1Zn-0.5Zr-0.5Ag合金具有最佳的抗拉强度、弹性模量和塑性匹配,其抗拉强度为210 MPa,弹性模量为50.7 GPa,延性率为24.8%。     

挤压态Mg-6Zn-xEr合金的微观结构和力学性能

研究铸态、挤压态和挤压峰值态的Mg-6Zn-xEr合金的微观组织和力学性能。结果表明,Er的加入可显著改善Mg-6Zn合金的力学性能,经过峰值时效后合金的力学性能得到进一步提高;挤压态Mg-6Zn-0．5Er合金经过峰值时效处理后具有最佳的拉伸强度。该合金的抗拉强度和屈服强度分别为329MPa和183MPa,伸长率为12％。这表明添加0．5％Er可显著提高Mg-6Zn合金的时效硬化行为。挤压峰值态Mg-6Zn-0．5Er合金较好的力学性能归因于结构的细化和β1相的析出强化。     

Effect of ageing treatment on microstructures,mechanical properties and corrosion behavior of Mg-Zn-RE-Zr alloy micro-alloyed with Ca and Sr

Effects of ageing treatment on the microstructures, mechanical properties and corrosion behavior of the Mg-4.2Zn-1.7RE-0.8Zr-xCa-ySr [x=0, 0.2 (wt.%), y=0, 0.1, 0.2, 0.4 (wt.%)] alloys were investigated. Results showed that Ca or/and Sr additions promoted the precipitation hardening behavior of Mg-4.2Zn-1.7RE-0.8Zr alloy and shortened the time to reaching peak hardness from 13 h to 12 h. The maximum hardness of 77.1±0.6 HV for the peak-aged Mg-4.2Zn-1.7RE-0.8Zr-0.2Ca-0.2Sr alloy was obtained. The microstructures of peak-aged alloys mainly consist of α-Mg phase, Mg₅₁Zn₂₀ phase and ternary T-phase. The Zn-Zr phase is formed within the α-Mg matrix, and the Mg₂Ca phase is formed near T-phase due to the enrichment of Ca in front of the solid-liquid interface. Furthermore, fine short rod-shaped β′₁ phase is precipitated within the α-Mg matrix in the peak-aged condition. The peak-aged Mg-4.2Zn-1.7RE-0.8Zr-0.2Ca-0.2Sr alloy exhibits optimal mechanical properties with an ultimate tensile strength of 208 MPa, yield strength of 150 MPa and elongation of 3.5%, which is mainly attributed to precipitation strengthening. In addition, corrosion properties of experimental alloys in the 3.5wt.% NaCl solution were studied by the electrochemical tests, weight loss, hydrogen evolution measurement and corrosion morphology observation. The results suggest that peak-aged alloys show reduced corrosion rates compared with the as-cast alloys, and minor additions of Ca and/or Sr improve the corrosion resistance of the Mg-4.2Zn-1.7RE-0.8Zr alloy. The peak-aged Mg-4.2Zn-1.7RE-0.8Zr-0.2Ca-0.2Sr alloy possesses the best corrosion resistance, which is mainly due to the continuous and compact barrier wall constructed by the homogeneous and continuous second phases.

     

Effect of Alloyed Mo on Mechanical Properties,Biocorrosion and Cytocompatibility of As-Cast Mg-Zn-Y-Mn Alloys

The influences of Mo contents on mechanical properties,biocorrosion and cytocompatibility of as-cast Mg-6Zn-8.16Y-2.02Mn-xMo(x=0.0,0.1,0.3,0.5,0.7 wt%) alloys were firstly investigated.Appropriate amount of Mo was conducive to grain refinement and the formation of long-period stacking ordered structure with continuous distribution,which was advantageous to mechanical properties and corrosion resistance.Mg-6Zn-8.16Y-2.02Mn-0.3Mo exhibited the ultimate tensile strength of 265.0 MPa,elongation of 13.5% and the lowest weight loss rate in Hank's solution.Moreover,the cell toxicity cultured in 25% extract was evaluated and the alloy with 0.3 wt% Mo exhibited the best cytocompatibility.Thus,the alloy was expected to become a novel biodegradable implant material.     

Effect of solid solution treatment on in vitro degradation rate of as-extruded Mg-Zn-Ag alloys

The degradation behaviors of the as-extruded and solution treated Mg-3Zn-xAg (x=0, 1, 3, mass fraction, %) alloys, as well as as-extruded pure Mg, have been investigated by immersion tests in simulated body fluid (SBF) at 37 °C. The as-extruded Mg-Zn(-Ag) alloys contained Mg₅₁Zn₂₀ and Ag₁₇Mg₅₄. While the quasi-single phase Mg-Zn(-Ag) alloys were obtained by solution treatment at 400 °C for 8 h. The quasi-single phase Mg-Zn(-Ag) alloys showed lower degradation rate and more homogeneous degradation than corresponding as-extruded Mg alloys. Degradation rate of solid-solution treated Mg-3Zn-1Ag and Mg-3Zn-3Ag was approximately half that of corresponding as-extruded Mg alloy. Moreover, the degradation rate of solid-solution treated Mg-3Zn and Mg-3Zn-1Ag was equivalent to that of as-extruded pure Mg. However, heterogeneous degradation also occurred in quasi-single phase Mg-Zn-Ag alloys, compared to pure Mg. So, preparing complete single-phase Mg alloys could be a potential and feasible way to improve the corrosion resistance.     

热处理对HA/Mg-Zn-Ca生物复合材料显微组织及性能的影响

采用剪切搅拌铸造结合热挤压工艺制备了1HA/Mg-3Zn-0.2Ca(质量分数,%)复合材料,研究了固溶及时效处理对挤压态1HA/Mg-3Zn-0.2Ca复合材料显微组织、力学性能及电化学腐蚀行为的影响。结果表明:挤压态复合材料经固溶处理(T4)后,第二相数量减少,晶粒尺寸增大,屈服强度降低,但延伸率和耐蚀性能有所提高。固溶超过3 h后,由于晶粒尺寸过分长大耐蚀能力又出现下降;固溶后时效处理(T6),复合材料屈服强度提高,耐蚀性变化不大。因此,对挤压态HA/Mg-Zn-Ca复合材料进行适当的固溶及时效处理可以提高复合材料的耐蚀性及延伸率。     

稀土Y元素对铸态镁合金组织与力学性能的影响

采用熔炼工艺制备了Mg-2.0Zn-0.2Ca与Mg-2.0Zn-0.2Ca-2Y合金,研究了两种合金的铸态组织及力学性能。结果表明,Y元素的添加细化了Mg-2.0Zn-0.2C合金的铸态组织。Mg-2.0Zn-0.2Ca合金主要由α-Mg与少量Mg₇Zn₃相组成,添加2wt%的Y后,改变了Zn在Mg基体中的固溶度,降低了其固溶强化效果,同时组织中形成了I相和W相。添加Y元素后,合金的规定塑性延伸强度升高,从41.0 MPa升高到50.6 MPa;伸长率降低,从12.6%降低到4.0%。     

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%。     

Effects of calcium addition on as-cast microstructure and mechanical properties of Mg-5Zn-5Sn alloy

The effects of Ca addition on the as-cast microstructure and mechanical properties of the Mg-5Zn-5Sn (mass fraction,%) alloy were investigated.The results indicate that an addition of 0.5%-1.5% (mass fraction) Ca to the Mg-5Zn-5Sn alloy not only refines the as-cast microstructure of the alloy but also causes the formation of the primary and/or eutectic CaMgSn phases with high thermal stability;an increase in Ca amount from 0.5% to 1.5% (mass fraction) increases the amount and size of the CaMgSn phase.In addition,Ca addition to the Mg-5Zn-5Sn alloy improves not only the tensile properties at room temperature and 150 ℃ but also the creep properties.Among the Ca-containing Mg-5Zn-5Sn alloys,the one added 0.5% (mass fraction) Ca obtains the optimum ultimate tensile strength and elongation at room temperature and 150 ℃,however,the alloy added 1.5% (mass fraction) Ca exhibits the optimum yield strength and creep properties.     

Zr含量对Mg-3Zn-1Y合金显微组织和腐蚀行为的影响

采用传统重力铸造法制备了Mg-3Zn-1Y-xZr (x=0,0.2,0.4,0.6)合金,并通过光学显微镜(OM)、扫描电镜(SEM)、失重和电化学实验研究了Zr含量对Mg-3Zn-1Y显微组织和腐蚀行为的影响.结果 表明:Mg-3Zn-1Y主要由α-Mg基质和Mg3YZr6(Ⅰ)相组成,Zr的加入没有改变第二相的类...