罗布泊沉积物多相态Mg同位素的分离提取及其古气候指示意义

晚中新世地球气候格局和生态系统转换的原因是学界长期关注并富有争议的科学问题。近期发现中高纬度海表温度在7~5.4 Ma期间发生了一次剧烈降温事件,支持大气CO_(2)下降驱动假说,但一直缺乏同时期陆地明显降温的证据。Mg是主要的造岩元素之一,在表生地质过程中会发生显著的同位素分馏,是古气候领域的新兴代用指标。本研究选取塔里木盆地的罗布泊深钻岩心,进行了不同深度沉积物的多相态Mg同位素(δ^(26)Mg)的淋滤提取,并与Rb/Sr、CIA等传统化学风化指标进行对比,探讨其古气候指示意义。结果显示,沉积物岩心中碳酸盐相、硅酸盐相和全岩样品之间存在显著的δ^(26)Mg组成差异,其平均值分别为(−2.37±0.47)‰、(−0.20±0.33)‰和(−0.80±0.24)‰(2SD,n=7)。沉积物碳酸盐相的δ^(26)Mg在化学淋滤提取过程中易受硅酸盐相污染,且难以区分湖泊自生碳酸盐和外来碎屑碳酸盐,记录的环境气候信号较为复杂。相反,分离提取实验结果表明,不同深度、不同岩性的罗布泊沉积岩心样品淋滤后的残余相基本由硅酸盐相组成,与Rb/Sr、CIA等传统化学风化指标相比,其δ^(26)Mg组成与晚中新世以来海表温度等其他气候记录有更好的一致性。研究结果表明,罗布泊沉积物硅酸盐相δ^(26)Mg可以指示其物源区化学风化强度的变化。因此,通过测定气候敏感区湖泊沉积物中硅酸盐相δ^(26)Mg记录,可以为探讨中国西部晚中新世以来的气候变化机制提供新的制约。

Ca含量对时效态Mg-6.5Al-xCa-1Sn-0.3Sr镁合金显微组织和性能的影响

通过XRD、SEM和性能测试研究了Ca含量的变化对时效态Mg-6.5Al-xCa-1Sn-0.3Sr(x=1,1.5,2,2.5)镁合金的显微组织和性能的影响。结果表明,时效态合金主要由α-Mg和Al_(2)Ca相组成,Al_(2)Ca相成网状分布。合金的抗拉强度和伸长率随着Ca加入量的增加而逐渐降低,当Ca含量为1%时合金的拉伸性能最佳,而合金的硬度随着Ca的加入而增加。在175℃、70 MPa下,Ca的添加使时效态合金的稳态蠕变速率降低。

Mg-Zn-Y系镁合金的研究现状与展望

镁合金作为“21世纪的绿色工程材料”,在航空航天、汽车、电子等领域具有广阔的应用前景。在诸多镁合金中,Mg-Zn-Y合金由于其独特的组织结构和优异的力学性能而成为研究热点。综述了近年来Mg-Zn-Y合金的研究现状。介绍了Mg-Zn-Y合金的物相与显微组织,主要对其存在的三种平衡相进行了简介,即准晶I相(Mg_(3)YZn_(6))、W相(Mg_(3)Y_(2)Zn_(3))和LPSO-Z相(Mg_(12)YZn);重点综述了主要合金元素(Zn、Y、Zr、Nd、Mn、Ca等)、变形加工处理对其微观组织及强韧化行为的作用规律,并总结了相应的铸态及变形态合金的力学性能。基于已有的研究基础展望了合金的未来发展方向。

等温处理对Mg-7Zn-x La镁合金半固态组织的影响

采用等温热处理法制备Mg-7Zn-xLa(x=0,0.1,0.3,0.5,wt.%)合金的半固态坯料。探索La元素及其含量对Mg-7Zn-xLa合金半固态组织的影响,分析La元素对固相颗粒粗化常数值的影响。结果表明:在相同的等温热处理工艺下,随La元素含量的增加,固相颗粒的平均尺寸和形状因子先减小后增加。当合金中La元素含量为0.3 wt.%时,对半固态组织的优化效果最佳。同时,添加La元素可以有效降低固相颗粒的粗化常数值,抑制固相颗粒的粗化。此外,通过分析二次凝固组织发现:随初生固相颗粒的部分熔化,液相中的Mg含量增加,导致次生α_(2)-Mg的数量和晶粒尺寸均明显增加。

Interplay of laser power and pore characteristics in selective laser melting of ZK60 magnesium alloys:A study based on in-situ monitoring and image analysis

This study offers significant insights into the multi-physics phenomena of the SLM process and the subsequent porosity characteristics of ZK60 Magnesium(Mg)alloys.High-speed in-situ monitoring was employed to visualise process signals in real-time,elucidating the dynamics of melt pools and vapour plumes under varying laser power conditions specifically between 40 W and 60 W.Detailed morphological analysis was performed using Scanning-Electron Microscopy(SEM),demonstrating a critical correlation between laser power and pore formation.Lower laser power led to increased pore coverage,whereas a denser structure was observed at higher laser power.This laser power influence on porosity was further confirmed via Optical Microscopy(OM)conducted on both top and cross-sectional surfaces of the samples.An increase in laser power resulted in a decrease in pore coverage and pore size,potentially leading to a denser printed part of Mg alloy.X-ray Computed Tomography(XCT)augmented these findings by providing a 3D volumetric representation of the sample internal structure,revealing an inverse relationship between laser power and overall pore volume.Lower laser power appeared to favour the formation of interconnected pores,while a reduction in interconnected pores and an increase in isolated pores were observed at higher power.The interplay between melt pool size,vapour plume effects,and laser power was found to significantly influence the resulting porosity,indicating a need for effective management of these factors to optimise the SLM process of Mg alloys.

Mn对Mg-2Sn镁合金显微组织和力学性能的影响

研究微量Mn元素对Mg-2Sn铸态和挤压态合金力学性能提升机制。采用铸造和热挤压方法将质量分数为0.3%、0.5%和1.0%的Mn元素添加到Mg-2Sn镁合金中,分别获得铸态和挤压态两种合金。采用电子万能材料试验机研究其力学性能;利用光学显微镜(OM)、扫描电子显微镜(SEM)、X射线衍射(XRD)和电子背散射衍射(EBSD)研究其微观组织变化规律。随着Mn含量从0.3%增加到1.0%,铸态合金中第二相由Mg 2 Sn相向Mg 2 Sn与α-Mn相共存转变。第二相的转变使得铸态合金屈服强度和抗拉强度显著提升,延伸率变化不大,其中当Mn含量为0.5%时,其综合性能最佳,抗拉强度为210.3 MPa,屈服强度为117.5 MPa,延伸率为12.2%。挤压态合金随着Mn含量的增加,合金抗拉强度和屈服强度均增加,但延伸率降低,这可能与高Mn含量的合金形成较高的位错有关,其中挤压态Mg-2Sn-0.5Mn合金具有最佳的综合力学性能,抗拉强度为240.4 MPa,屈服强度为186.4 MPa,延伸率为13.1%。微量Mn元素可显著提升铸态和挤压态合金的抗拉强度和屈服强度,其中Mg-2Sn-0.5Mn合金综合力学性能最优。

Mg-6.42Al-3.22Sn镁合金轧制后的显微组织与力学性能

为了改善镁合金单道次大压下量轧制变形能力,提高轧制效率,采用扫描电镜和拉伸试验机等手段研究了不同变形量下单衬板轧制和双衬板轧制Mg-6.42Al-3.22Sn镁合金的显微组织和力学性能变化。结果表明,单衬板轧制镁合金试样的下表面裂纹状态优于上表面,轧制温度为400℃时镁合金试样上下表面未见裂纹,而双衬板轧制镁合金在轧制温度为350℃及以上时都未见明显裂纹。单衬板轧制和双衬板轧制镁合金试样的平均晶粒尺寸和第二相颗粒尺寸都随着变形量增加而减小。在相同变形量下,单衬板轧制和双衬板轧制镁合金的屈服强度和抗拉强度相当,且双衬板轧制镁合金的断后伸长率和应变硬化指数高于后者,更有利于后续加工变形,这主要与双衬板轧制有助于将镁合金试样上下表面的剪切应变转变为压应变,更有利于抑制裂纹扩展和具有更高的抵抗均匀塑性变形的能力有关。

塔里木盆地鹰山组白云岩成因与Mg同位素证据

中—下奥陶统鹰山组作为塔里木盆地中央隆起区潜在的重要勘探接替层系,其白云岩成因认识仍不清楚,因此制约了对该区域的进一步勘探。鹰山组由下至上依次发育白云岩、白云质灰岩和灰岩,表明发生了灰岩向白云岩的交代转化过程。交代白云岩的形成需要足够的含镁流体和长期的镁泵输送机制,而新兴的Mg同位素技术在示踪白云石化流体来源和迁移路径方面已经取得良好效果。因此,本研究通过系统采集鹰山组白云岩、白云质灰岩和灰岩,开展岩石学、微量元素、碳氧同位素和Mg同位素测试。实验结果显示,鹰山组发育6类岩石,分别是泥晶-微晶白云岩(D1)、粉晶-细晶白云岩(D2)、颗粒白云岩(D3)、中晶-粗晶白云岩(D4)、白云质灰岩(DL)和灰岩(L)。鹰山组碳酸盐岩的δ^(13)C_(V-PDB)值为-2.10‰~-0.37‰(平均值-1.37‰),δ^(18)O_(V-PDB)值为-7.51‰~-3.54‰(平均值-5.41‰),δ^(26)Mg值为-4.03‰~-1.28‰(平均值-2.55‰)。δ^(26)Mg、Na含量、Sr/Ba、Mn/Fe、δ^(13)C_(V-PDB)、δ^(18)O_(V-PDB)、古盐度(Z)和古温度(T)在垂向上显示出一定的联动性和系统性。通过综合分析与讨论得出以下几点认识:(1)鹰山组δ^(26)Mg值垂向变化趋势与沉积旋回具有密切联系,沉积旋回的顶部为富镁流体源区,旋回界面为流体迁移通道;(2)识别出4种Mg同位素变化趋势与白云石化流体迁移规律,即云灰互层结构(L→DL→D)、准同生白云岩结构(D1→D2)、渗透回流白云岩结构(D1→D2→D3→D4→L)和埋藏白云岩结构(D4→DL/D);(3)鹰山组白云岩形成主要与海平面周期性波动有关,海平面下降时,蒸发作用促使局限水体中富集Mg^(2+),并且富镁流体会沿着下伏高孔高渗的颗粒灰岩垂向迁移至下伏地层,有利于白云石化作用的持续进行,当富镁流体遇到孔隙度不发育的泥晶灰岩时,富镁流体无法进入矿物晶格中,白云石化作用停止。海平面上升时,局限水体转变为开阔水体,海水与富镁流体源区相互混合,降低了流体的白云石化驱动力,致使白云石化作用逐渐减弱,从而发育灰质白云岩和灰岩;(4)除受海平面控制外,深埋藏阶段经历的多期交代、重结晶或热液作用也有利于鹰山组白云岩的形成;(5)白云石化作用对鹰山组沉积储层具有建设性意义,早期白云石化作用有利于孔隙的继承和保存,而晚埋藏和热液白云石化对储层起破坏作用。

Rheological behavior of semi-solid Mg_2Si/AM60 magnesium matrix composites at steady state

The microstructure and rheological behavior of semi-solid Mg2Si/AM60 magnesium matrix composite at steady state were investigated.The results show that the primary α-Mg phases are knapped by mechanical stirring and the Chinese script type reinforced Mg2Si phases exist in liquid phase and grain boundary.The analysis of apparent viscosity indicates that the apparent viscosity of semi-solid Mg2Si/AM60 magnesium matrix composite at steady state increases with increasing the volume fraction of Mg2Si and solid fraction of primary α-Mg,but decreases with increasing the shearing rate and shearing time,and the apparent viscosity keeps stable when shearing time reaches 300 s.

Effects of little Ce addition on as-cast microstructure and creep properties of Mg-3Sn-2Ca magnesium alloy

The effects of little Ce addition on the as-cast microstructure and creep properties of Mg-3Sn-2Ca magnesium alloy were investigated.The results indicate that adding 0.5%(mass fraction)Ce to Mg-3Sn-2Ca alloy does not cause the formation of any new phase in the alloy.However,an interesting microstructural change in the as-cast Mg-3Sn-2Ca alloy added with 0.5%Ce is observed. After adding 0.5%Ce to Mg-3Sn-2Ca alloy,not only the volume fraction of CaMgSn phase in the alloy is decreased but also the CaMgSn phases in the alloy are refined.In addition,adding 0.5%Ce to Mg-3Sn-2Ca alloy can also improve the creep-resistant properties of the alloy.After adding 0.5%Ce to Mg-3Sn-2Ca alloy,the second creep rate of the alloy at 150℃and 70 MPa for 100 h changes from 3.28×10-8to 1.81×10 -8s -1.

Microstructures and tensile properties of as-cast Mg-5Sn-1Si magnesium alloy modified with trace elements of Y,Bi,Sb and Sr

The microstructures and mechanical properties of as-cast Mg-5 Sn-1 Si magnesium alloy modified with trace elements Y,Bi,Sb and Sr were investigated and compared.Results show that the microstructure of the as-cast Mg-5 Sn-1 Si alloy consists ofα-Mg,Mg_(2) Si,Mg_(2) Sn and Mg_(2)(Si_xSn_(1-x))phases.After adding 0.8 wt.%Y,0.3 wt.%Bi,0.9 wt.%Sb and 0.9 wt.%Sr,respectively into the Mg-5 Sn-1 Si magnesium alloy,Mg_(24)Y_(5),Mg_(3) Bi_(2),Mg_(3) Sb_(2) and Mg_(2) Sr phases are precipitated accordingly.Trace elements can refineα-Mg grain and Chinese scriptshaped Mg_(2) Si phase.Refinement efficiency of different trace elements onα-Mg grain and Mg_(2) Si phase is varied.Sr element has the best refinement effect,followed by Sb and Bi,while Y has the least refinement effect.Mg-5 Sn-1 Si-0.9 Sr alloy has higher tensile properties than the other three modified alloys.The refinement mechanism of Y,Bi and Sr elements on Mg-5 Sn-1 Si magnesium alloy can be explained by the growth restriction factors and the solute undercooling.For Mg-5 Sn-1 Si-0.9 Sb alloy,the heterogeneous nuclei of Mg_(3) Sb_(2) phase is the main reason for the refinement of grains and second phases.

Effects of RE on the Microstructure of Mg-8Zn-4Al Magnesium Alloys

The effects of RE on the microstrcture of as-cast Mg-8Zn-4Al magnesiu m alloys were investigated. The results show that the solidification range of Mg-8Zn-4Al -xRE alloys increases with RE additions. A binary eutectic reaction can arise and produce a new phase (Mg3Al4Zn2RE) and the temperature of phase transformation point of the ne w phase is 412.85℃. In Mg-8Zn-4Al-1.5RE alloy, a small amount of Mg3Al4Zn2RE phase and ε phases are found besides α(Mg),φ and τ phases. Also microstructures of Mg-8Zn-4Al alloy s can be refined by addition of 1.5% RE obviously.

Corrosion resistance of cerium conversion film electrodeposited on Mg-Gd-Y-Zr magnesium alloy

The cerium conversion film was applied to improving the corrosion resistance of Mg-Gd-Y-Zr magnesium alloy. The film was electrodeposited on the surface of the Mg-RE alloy in cerium nitrate solution. The compositions and morphologies were analyzed by X-ray diffraction(XRD), scanning election microscopy (SEM). The corrosion behaviors of the film were investigated electrochemical impedance spectroscopy (EIS), potentiodynamic polarization tests and immersion tests. The results show that the optimum parameters for electrochemical deposition are as follows: pH 10.0, time 30 min, 50 mmol/L Na2CO3 and temperature 25 ℃ by the designed experiments according to the orthogonal table L(9, 34). The corrosion protection efficiency is dependent on the deposition parameters. The cerium conversion film shows better corrosion protection behavior than chromate conversion film on Mg-Gd-Y-Zr magnesium alloy.

Microstructure and mechanical properties of Mg-6Al magnesium alloy with yttrium and neodymium

The effects of rare earth(RE) elements Y and Nd on the microstructure and mechanical properties of Mg-6Al magnesium alloy were investigated.The results show that a proper level of RE elements can obviously ref ine the microstructure of Mg-6Al magnesium alloys,reduce the quantity of β-Mg17Al12 phase and form Al2Y and Al2Nd phases.The combined addition of Y and Nd dramatically enhances the tensile strength of the alloys in the temperature range of 20-175℃.When the content of RE elements is up to 1.8%,the values of tensile strength at room temperature and at 150℃ simultaneously reach their maximum of 253 MPa and 196 MPa,respectively.The main mechanisms of enhancement in the mechanical properties of Mg-6Al alloy with Y and Nd are the grain ref ining strengthening and the dispersion strengthening.

Effects of heat treatment on corrosion behaviors of Mg-3Zn magnesium alloy

The effects of two kinds of heat treatments T4(solution treatment) and T6(aging treatment) on the corrosion behaviors of Mg-3Zn magnesium alloy were studied by electrochemical measurements and scanning electron microscopy(SEM) .It is found that zinc element enriches along grain boundaries to exhibit a network microstructure for both T4-and T6-treated alloy.For T6 treatment,larger MgZn particles form mainly on grain boundary and fine MgZn particles precipitate on matrix.Compared with cast alloy,T4 treatment could decrease the amounts of MgZn particles,and decrease the zinc content of zinc-rich net-segregation.Electrochemical measurements show that T4 treatment increases the corrosion resistance while T6 treatment decreases the corrosion resistance of Mn-3Zn alloy.

Growth process and corrosion resistance of micro-arc oxidation coating on Mg-Zn-Gd magnesium alloys

A Mg-6Zn-3Gd(mass fraction,%) alloy,noted as ZG63,was coated by different micro-arc oxidation(MAO) processes,and the coating structure and corrosion resistance of the alloy were studied using scanning electron microscopy(SEM),glancing angle X-ray diffractometry(GAXRD) and various electrochemical methods.The micro-arc oxidation process consists of three stages and corresponds with different coating structures.In the initial stage,the coating thickness is linearly increased and is controlled by electrochemical polarization.In the second stage,the coating grows mainly inward and accords with parabolic regularity.In the third stage,the loose coating forms and is controlled by local arc light.The looser coating is mainly composed of MgSiO3 and the compact coating is mainly composed of MgO.From micro-arc oxidation stage to local arc light stage,the corrosion resistance of the coated alloy firstly increases and then decreases.The satisfied corrosion resistance corresponds to the coating time ranging from 6 to10 min.

Fracture behavior of high strength Mg-Gd-Y-Zr magnesium alloy

The fracture behavior of a permanent mould casting Mg-8.57Gd-3.72Y-0.54Zr(mass fraction,%)(GW94) alloy was investigated under different thermal conditions,including as-cast,solution-treated,peak-aged,and over-aged states.Scanning electron microscopy(SEM) and optical microscopy(OM) were employed to examine the crack nucleation and fracture model.The results indicate that the GW94 alloy shows different behaviors of crack initiation and fracture under different thermal conditions. During tensile test at room temperature,the fracture model of the as-cast GW94 alloy is quasi-cleavage,while that of the solution-treated alloy is transgranular cleavage.It is a mixed pattern of transgranular and intergranular fracture for both the aged conditions.Large cavities formed at grain boundaries are observed in the peak-aged sample tested at 300℃,corresponding to the intergranular fracture.Localized plastic deformation at grain boundaries is also observed and corresponds to the high elongation at 300℃.

Hot compression deformation behavior of the Mg-Al-Y-Zn magnesium alloy

The hot deformation behavior of a Mg-Al-Y-Zn magnesium alloy was investigated by hot compressive testing on a Gleeble-1500 thermal simulator at the temperature ranging from 523 to 673 K with the strain rate varying from 0.001 to 1 s^-1. The relationships among flow stress, strain rate, and deformation temperature were analyzed, and the deformation activation energy and stress exponent were calculated. Microstructure evolution of the alloy under different conditions was examined. The results indicated that the maximum value of the flow stress increased with the decrease of deformation temperature or the increase of strain rate. Under the present deformation conditions, dynamic recrystallization （DRX） occurred in the alloy, which was the main softening mechanism during deformation at elevated temperature. The deformation temperature and strain had significant effects on the microstructure of the alloy.

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.

Effects of Cu addition on microstructureand mechanical properties of as-cast Mg-6Znmagnesium alloy

The application of Mg-Zn binary alloys is restricted due to their developed dendritic microstructure and poor mechanical properties. In this study, an alloying method was used to improve the mechanical properties of Mg-Zn alloy. The Mg-6Zn magnesium alloys microalloyed with varying Cu content(0, 0.8, 1.5, 2.0 and 2.5wt.%) were fabricated by permanent mould casting, and the effects of Cu content on the microstructure and mechanical properties of as-cast Mg-6Zn alloys were studied using OM, SEM, XRD and tensile tests at room temperature. The obtained results show that the addition of Cu not only can refine the grains effectively, but also can modify the eutectic morphology and improve the mechanical properties of the alloys. The main phases of the studied alloys include α-Mg, MgZn_2, Mg_2Cu and CuMgZn. When the content of Cu exceeds 0.8wt.%, Mg_2Cu phase appears. Meanwhile, the eutectic morphology is modified into dendritic shape or lamellar structure, which has an adverse effect on the tensile properties. Furthermore, among the investigated alloys, the alloy containing 0.8% Cu shows an optimalultimate tensile strength of 196 MPa, while the alloy with 1.5wt.% Cu obtains an excellent elongation of 7.22%. The experimental alloys under different Cu contents show distinguishing fracture behaviors: the fracture of the alloy with 0.8wt.% Cu reveals a mixed mode of inter-granular and quasi-cleavage, while in other investigated alloys, the fracture behaviors are dominated by cleavage fracture.