Plastic deformation behavior of Mg97Zn1Y2 extruded alloys

The mechanical properties of the Mg97ZnlY2 extruded alloy containing the long-period stacking ordered phase, the so-called LPSO-phase, with a volume fraction of 24%-25%, were examined by compression tests and cyclic tension-compression deformation tests. The plastic behavior of the extruded alloys with compositions of Mg99.2Zn0.2Y0.6 and Mg89Zn4Y7 （molar fraction, %）, which were almost the same compositions of Mg matrix phase and LPSO phase in Mg97Zn1Y2 Mg/LPSO two-phase alloy, respectively, were also prepared. By comparing their mechanical properties, the strengthening mechanisms operating in the Mg97Zn1 Y2 extruded alloy were discussed. Existence of the LPSO-phase strongly enhanced the refinement of Mg matrix grain size during extrusion, which led to a large increment of the strength of alloy. In addition, the LPSO-phases, which were aligned along the extrusion direction in Mg97Zn1Y2 extruded alloy, acted as hardening phases, just like reinforced fibers.     

Microstructure and Mechanical Properties of AZ91 Alloys by Addition of Yttrium

Effects of yttrium (Y) on the microstructure and properties of as-cast Mg-Al-Zn (AZ91) alloys were studied. Y additions not only change the microstructure but also influence the mechanical properties of AZ91 alloy. AZ91 unmodified alloys under as-cast state indicate that eutectic phase Mg₁₇Al₁₂ is continuous and reticulated. Yttrium addition to AZ91 casting alloys has an important influence on the primary-phase and precipitation. When the Y content is 0.3 wt.%, no Y-containing compound was observed. When the Y content is 0.6 and 0.9 wt.%, Al₂Y phase formed in the alloy and the growth morphology of eutectic Mg₁₇Al₁₂ phase is modified. When the Y content is further increased to 1.2 wt.%, the Al₂Y phase becomes coarser and Mg₁₇Al₁₂ transforms into a cotton-shape structure. The results showed that Y can improve significantly as-cast microstructure of AZ91 alloys, refining Mg₁₇Al₁₂ phase and increasing in hardness and strength and decreasing in impact toughness and elongation.     

Morphological evolutions of cast and melt-spun Mg_(97)Zn_1Y_2 alloys during deformation and heat-treating

Mg_(97)Zn_1Y_2 alloy has been studied as an elevated temperature creep resistant Mg-based alloy for nearly ten years.While, the strength of the cast Mg_(97)Zn_1Y_2 alloy with long-period stacking(LPS) structure is lower than that of the commercial AZ91 alloy at room temperature.The microstructure evolutions in Mg_(97)Zn_1Y_2(molar fraction,%) alloys with LPS phase,processed by rolling and annealing the as-cast alloy and rapidly solidifying/melt-spinning and age treating at different temperatures respecti...     

Mg94TM(Zn,Cu,Ni)2Y4合金的铸态组织及摩擦磨损性能

利用普通铸造法制备了Mg94TM(Zn,Cu,Ni)2Y4三种合金,并研究其铸态组织特征、物相组成及耐磨性能.Mg94Zn2Y4和Mg94Cu2Y4合金组织呈现[明显的树枝晶结构,而Mg94Ni2Y4以等轴晶为主;Mg94Cu2Y4和Mg94Ni2Y4两种合金的金属间化合物组成要比Mg94Zn2Y4合金复杂.三种合金材料中,Mg94Zn2Y4合金的硬度最低,耐磨性最差,其磨损机制均主要表现为犁沟磨损、粘着磨损和氧化磨损.     

Zn、Y含量的变化对Mg-Zn-Y合金组织和性能的影响

以Mg6Zn2Y为基础研究了Zn、Y含量的变化对Mg-Zn-Y基合金组织和性能的影响.结果表明铸态下增加1%Zn的合金的组织变得粗大,抗拉强度降低约10%,伸长率降低25%;同时添加1%Zn和1%Y的合金组织明显细化,抗拉强度和伸长率分别提高11%和17%;挤压后由于Y的加入形成了高熔点的化合物相,合金受这些相抑制,没有发生动态再结晶,力学性能因挤压变形得到不同程度的提高,对比分析Mg7Zn3Y合金拥有抗拉强度355 MPa和伸长率4.5%较好的综合性能.     

Mn添加对挤压态Mg-Zn-Y-Nd合金微观组织和腐蚀行为的影响

通过光学显微镜,配备能量色散光谱仪的扫描电子显微镜,X射线衍射仪,浸泡法和电化学测试的方法研究了Mn的添加对挤压Mg-Zn-Y-Nd合金在3.5wt.％NaCl溶液中的微观组织和腐蚀行为的影响。结果表明,在研究的Mg-Zn-Y-Nd合金中添加Mn可以诱导Mg3Y2Zn3（I相）沉淀,可以抑制热挤压过程中动态再结晶（DRX）晶粒的粗化。同时,添加了Mn也可以提高合金的耐腐蚀性。不含Mn的Mg-5.6Zn-1Y-0.4Nd合金与含锰1.0 wt.％的Mg-5.6Zn-1Y-0.4Nd合金腐蚀速率分别为18.78 mm·y-1和9.89mm·y-1。而耐腐蚀性的提高主要归因于腐蚀产物层保护性的增强。     

Effect of long-period stacking ordered phase on mechanical properties of Mg97Zn1Y2 extruded alloy

The mechanical properties of Mg97Zn1Y2 extruded alloy, composed of Mg matrix phase and a long-period stacking ordered phase, the so-called LPSO phase, with a volume fraction of approximately 24%, were investigated using compression tests at room temperature. The microstructure was varied to a large degree by various heat treatments at high temperatures above 400 °C, and the relationship between the microstructure and mechanical properties was clarified. The plastic behavior of the Mg/LPSO two-phase alloy was compared with that of Mg99.2Zn0.2Y0.6 alloy, composed almost Mg-solid-solution phase, and the strengthening mechanisms at work in the Mg97Zn1Y2 extruded alloy are discussed. The existence of the LPSO phase strongly enhanced the refinement of Mg matrix grains during extrusion, which led to a large increase in yield stress through the Hall–Petch relationship. In addition, the LPSO phases, which were aligned along the direction of extrusion in the Mg97Zn1Y2 extruded alloy, acted as hardening phases, being roughly coordinated with the short-fiber reinforcement mechanism.     

Microstructure,anticorrosion, biocompatibility and antibacterial activities of extruded Mg−Zn−Mn strengthened with Ca

To find suitable biodegradable materials for implant applications, Mg?6Zn?0.3Mn?xCa (x=0, 0.2 and 0.5, wt.%) alloys were prepared by semi-continuous casting followed by hot-extrusion technique. The microstructure and mechanical properties of Mg?6Zn?0.3Mn?xCa alloys were investigated using the optical microscope, scanning electron microscope and tensile testing. Results indicated that minor Ca addition can slightly refine grains of the extruded Mg?6Zn?0.3Mn alloy and improve its strength. When 0.2 wt.% and 0.5 wt.% Ca were added, the grain sizes of the as-extruded alloys were refined from 4.8 to 4.6 and 4.2 μm, respectively. Of the three alloys studied, the alloy with 0.5 wt.% Ca exhibits better combined mechanical properties with the ultimate tensile strength and elongation of 334 MPa and 20.3%. The corrosion behaviour, cell viability and antibacterial activities of alloys studied were also evaluated. Increasing Ca content deteriorates the corrosion resistance of alloys due to the increase of amount of effective cathodic sites caused by the formation of more Ca₂Mg₆Zn₃ phases. Cytotoxicity evaluation with L929 cells shows higher cell viability of the Mg?6Zn?0.3Mn?0.5Ca alloy compared to Mg?6Zn?0.3Mn and Mg?6Zn?0.3Mn? 0.2Ca alloys. The antibacterial activity against Staphylococcus aureus is enhanced with increasing the Ca content due to its physicochemical and biological performance in bone repairing process.     

Effect of Cu addition on microstructure and properties of Mg-10Zn-5Al-0.1Sb high zinc magnesium alloy

To improve the strength,hardness and heat resistance of Mg-Zn based alloys,the effects of Cu addition on the as-cast microstructure and mechanical properties of Mg-10Zn-5Al-0.1Sb high zinc magnesium alloy were investigated by means of Brinell hardness measurement,scanning electron microscopy (SEM),energy dispersive spectroscopy (EDS),XRD and tensile tests at room and elevated temperatures.The results show that the microstructure of as-cast Mg-10Zn-5Al-0.1Sb alloy is composed of α-Mg,t-Mg32(Al,Zn)49,φ-Al2Mg5Zn2 and Mg3Sb2 phases.The morphologies of these phases in the Cu-containing alloys change from semi-continuous long strip to black herringbone as well as particle-like shapes with increasing Cu content.When the addition of Cu is over 1.0wt.%,the formation of a new thermally-stable Mg2Cu phase can be observed.The Brinell hardness,room temperature and elevated temperature strengths firstly increase and then decrease as the Cu content increases.Among the Cu-containing alloys,the alloy with the addition of 2.0wt.% Cu exhibits the optimum mechanical properties.Its hardness and strengths at room and elevated temperatures are 79.35 HB,190MPa and 160MPa,which are increased by 9.65%,21.1% and 14.3%,respectively compared with those of the Cu-free one.After T6 heat treatment,the strengths at room and elevated temperatures are improved by 20% and 10%,respectively compared with those of the as-cast alloy.This research results provide a new way for strengthening of magnesium alloys at room and elevated temperatures,and a method of producing thermally-stable Mg-10Zn-5Al based high zinc magnesium alloys.     

Y对Mg-3Al-1Zn镁合金铸态组织的影响

研究Y对Mg-3Al-1Zn镁合金铸态组织的影响。结果表明,在Mg-3Al-1Zn合金中加入w(Y)=0.3%和w(Y)=0.6%对合金组织中合金相种类没有影响,但当w(Y)=0.9%时有Al3Y相存在。同时,加入微量Y使合金组织中Mg17Al12相基本上转变为断续状和颗粒状分布,且其分布具有一定方向性,同时其数量也逐渐减少。此外,研究结果还发现微量Y对Mg-3Al-1Zn合金的组织有一定的细化作用。     

通过凝固冷却速率调整Zn-1Mg-(0.5Mn,0.5Ca)合金的显微组织和显微硬度

生物可降解锌基合金,特别是添加合金元素的锌-镁(Zn-Mg)合金,已获得广泛研究以改善其力学性能和腐蚀性能.由于这些性能主要依赖于合金的显微组织,因此任何评价都应该从了解影响其形成的条件开始.本研究旨在探讨凝固冷却速率对Zn-1Mg-(0.5Ca,0.5Mn)(质量分数,％)合金瞬态凝固过程中显微组织演化的影响.结果表...     

Single and double aging treatments on Mg97Zn1Y2 alloy

The development of magnesium alloys was limited due to the low absolute strength and poor corrosion resistance. It was found that the optimal performance could not be achieved in some alloys by a single quenching and aging treatment, but could be achieved after a graded aging or multiple-stage aging heat treatment. The Mg97Zn1Y2 alloy was prepared and subjected to single and double aging treatments. Single aging was carried out at 250 ℃ for 6 to 15 h. For double aging, the first step was performed the same as the single aging. The second step was performed at 350 ℃ for 12 h. The microstructure and properties of the alloy with single and double aging were analyzed by means of hardness measurement, optical microscopy, scanning electron microscopy, X-ray diffraction, and polarization curve measurements. Results show that the precipitated nanoscale phases are formed during aging, and evenly distributed in the matrix. Compared with the single aging treatment, the hardness and corrosion resistance of the alloy are further improved due to the double aging treatment.     

锆元素对Mg_(97)Y_2Zn_1镁合金微观组织和力学性能的影响(英文)

研究锆元素对Mg97Y2Zn1镁合金微观组织和力学性能的影响。锆元素的添加可以细化铸态Mg97Y2Zn1合金的组织。在挤压过程中,Mg97Y2Zn1镁合金在原始晶界和第二相周围优先形核。锆元素的添加促进合金的再结晶过程,这是因为锆元素的添加使合金形成更多的晶界,从而提高了再结晶的形核率。此外,锆元素的添加还能够提高合金的强度和伸长率等力学性能。     

Tensile fracture of as-cast and hot rolled Mg-Zn-Y alloy with long-period stacking phase

An experimental Mg97Zn1Y2(molar fraction,%)alloy was produced by rolling the as-cast alloy.The microstructure of the alloy is composed of theα-Mg(also marked as 2H-Mg with reference to long-period stacking structure according to hexagonal close packed structure)and long-period stacking(LPS)phase.Tensile tests of Mg97Zn1Y2 alloy in comparison with pure Mg were conducted.The fracture morphologies of the tensile specimens were characterized and the microstructures near fracture surface were observed.The results show that the rolled Mg97Zn1Y2 alloy shows a mixed fracture mode including dimples indicating a ductile fracture pattern and a small fraction of cleavage planes indicating a brittle fracture pattern,which is different from the single brittle fracture of the as-cast alloy.In addition,the plastic deformation is mainly from dislocations induced strain with small strengthening effect during plastic deformation in the as-cast Mg97Zn1Y2 alloy,and the strain hardening rate is similar to that of the as-cast pure magnesium.The deformation mechanism of Mg97Zn1Y2 alloy is different from that of the pure magnesium according to a metallographical observation that whether twins are found or not.The strengthening effect hardly exists in the rolled Mg97Zn1Y2 alloy under the same dislocations induced strain,which is different from that of the as-cast alloy with moderate strengthening effect.     

Effects of titanium addition on structural,mechanical, tribological,and corrosion properties of Al−25Zn−3Cu and Al−25Zn−3Cu−3Si alloys

To investigate the effect of grain refinement on the material properties of recently developed Al−25Zn−3Cu based alloys, Al−25Zn−3Cu, Al−25Zn−3Cu−0.01Ti, Al−25Zn−3Cu−3Si and Al−25Zn−3Cu−3Si−0.01Ti alloys were produced by permanent mold casting method. Microstructures of the alloys were examined by SEM. Hardness and mechanical properties of the alloys were determined by Brinell method and tensile tests, respectively. Tribological characteristics of the alloys were investigated by a ball-on-disc type test machine. Corrosion properties of the alloys were examined by an electrochemical corrosion experimental setup. It was observed that microstructure of the ternary A1−25Zn−3Cu alloy consisted of α, α+η and θ (Al₂Cu) phases. It was also observed that the addition of 3 wt.% Si to A1−25Zn−3Cu alloy resulted in the formation of silicon particles in its microstructure. The addition of 0.01 wt.% Ti to the Al−25Zn−3Cu and Al−25Zn−3Cu−3Si alloys caused a decrement in grain size by approximately 20% and 39% and an increment in hardness from HRB 130 to 137 and from HRB 141 to 156, respectively. Yield strengths of these alloys increased from 278 to 297 MPa and from 320 to 336 MPa while their tensile strengths increased from 317 to 340 MPa and from 334 to 352 MPa. Wear resistance of the alloys increased, but corrosion resistance decreased with titanium addition.     

固溶态和挤压态Mg-xLi-3Al-2Zn-0.5Y(x=4,8,12)合金的显微组织和腐蚀行为

研究固溶态和挤压态Mg-xLi-3Al-2Zn-0.5Y(x=4,8,12,质量分数,%)合金的显微组织和腐蚀行为。结果表明,当锂含量从4%增加到12%,合金基体由α-Mg单相转变为α-Mg+β-Li双相,再转变为β-Li单相。Mg-4Li-3Al-2Zn-0.5Y和Mg-12Li-3Al-2Zn-0.5Y合金具有晶间腐蚀和点蚀的混合腐蚀特征,前者与沿晶界析出的AlLi相有关,后者与第二相与基体之间的高电位差有关。挤压态合金的耐蚀性优于固溶态合金。挤压态Mg-8Li-3Al-2Zn-0.5Y合金具有最低腐蚀速率(P_W=(0.63±0.26)mm/a),主要归因于该合金的第二相分布更均匀、通过牺牲β-Li相形成的保护性α-Mg相和相对完整的更均匀分布的氧化膜。     

Mn-promoting formation of a long-period stacking-ordered phase in laser-melted Mg alloys to enhance degradation resistance

Magnesium (Mg) alloys are promising candidates for use as biomedical implant materials. However, their very fast degradation rate greatly restricts their application. A rare earth phase possessed with a long-period stacking-ordered (LPSO) structure was in favor of enhancing the degradation resistance of Mg alloys. In fact, the formation of the LPSO phase in Mg alloys depends on their stacking fault energy. The lower the stacking fault energy, the more the LPSO phase formed. In this study, manganese (Mn) was alloyed to Mg alloy ZK30–10Gd (containing 3 wt.% Zn and 10 wt.% Gd) via selective laser melting to promote the formation of the LPSO phase. As an alloying element, Mn could be in favor of reducing stacking fault energy due to the fact that the large difference between the atomic radius of Mn and that of Mg induced large lattice distortion to facilitate forming stacking faults. The results showed that as the Mn content increased from 0 to 1.2 wt.%, the area fraction of LPSO phase increased from 12.22% to 22.37%, meanwhile the area fraction of (Mg,Zn)₃Gd phase decreased from 9.31% to 2.32%. The ZK30–10Gd–0.6Mn possessed the highest degradation resistance (weight loss rate 0.38 mg · cm⁻² · day⁻¹). The enhancement of degradation resistance had two reasons. On the one hand, more LPSO phase provided more sites for nucleation of degradation products, which could promote the formation of a homogeneous and compact degradation product film to protect the Mg matrix. On the other hand, the inhibition of (Mg,Zn)₃Gd phase precipitation could reduce galvanic corrosion.     

Correlations among stress corrosion cracking,grain-boundary microchemistry,and Zn content in high Zn-containing Al–Zn–Mg–Cu alloys

The correlations among the corrosion behaviour, grain-boundary microchemistry, and Zn content in Al–Zn–Mg–Cu alloys were studied using stress corrosion cracking (SCC) and intergranular corrosion (IGC) tests, combined with scanning electron microscopy (SEM) and high-angle angular dark field scanning transmission electron microscopy (HAADF-STEM) microstructural examinations. The results showed that the tensile strength enhancement of high Zn-containing Al–Zn–Mg–Cu alloys was mainly attributed to the high density nano-scale matrix precipitates. The SCC plateau velocity for the alloy with 11.0 wt.% Zn was about an order of magnitude greater than that of the alloy with 7.9 wt.% Zn, which was mainly associated with Zn enrichment in grain boundary precipitates and wide precipitates-free zones. The SCC mechanisms of different Zn-containing alloys were discussed based on fracture features, grain-boundary microchemistry, and electrochemical 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...     

Cr-Bi对Mg-8Zn-4Al合金铸态组织及时效沉淀相演变的影响

利用扫描电子显微镜(SEM)和X射线衍射(XRD)等分析手段研究了Bi、Cr-Bi复合添加对Mg-8Al-4Zn合金铸态组织及时效沉淀相演变的影响。结果表明:Cr-Bi复合添加能有效改善合金的铸态组织,使连续网状相断开呈短杆或颗粒状。Bi、Cr-Bi复合添加的合金经350℃×12 h+160℃时效,其沉淀硬化曲线呈现典型的温时效。Cr-Bi复合添加的合金时效初期硬化速率较高,20 h就达到峰值硬度的97%,时效48 h达到峰值硬度92.44 HV,过时效阶段硬度下降速度比较缓慢。Mg-8Zn-4Al-0.5Bi合金经350℃×12 h+160℃×120 h时效后主要有MgZn2、Mg3Bi2和单Bi相,呈短杆或细小颗粒状弥散分布在基体上;Cr-Bi复合添加的合金经350℃×12 h+160℃×144 h时效后,除短杆或细小颗粒状的MgZn2相外还有Cr、Al12Cr3等沉淀相,没有发现粗大的MgZn相,且沉淀相与单独添加Bi经120 h时效的合金相比更加细小、致密、弥散均匀分布。