TiO2与MnCl2对Mg合金旧料组织性能的影响

测试了含有不同量的TiO2或MnCl2的熔剂对Mg合金废旧料的力学性能、组织、断口形貌以及腐蚀行为的影响．结果表明，TiO2和MnCl2均可以降低Mg合金废旧料中的Fe含量，TiO2的除Fle效果可达0．0053％以下，优于MnCl2的效果．通过降低Fe量可以提高试样的σb和δ，MnCl2的效果优于TiO2．采用含30％TiO2或MnCl2的熔剂对Mg合金废旧料进行净化处理后，其σb和δ可分别大于185．3MPa和3．71％，即达到了AZ91Mg合金新料的性能指标．研究还表明，Ti02或MnCl2加入量一定时，均可以提高Mg合金的耐蚀性．但当熔剂中MnCl2的含量高于30％时，Mg合金的耐蚀性反而下降．Ti02有助于使γ相成粒状或小岛状析出，并具有很好的细化晶粒的效果．     

添加稀土Er于熔剂中对铸态AZ91镁合金组织与性能的影响

研究了熔炼时在熔剂(42%MnCl2 53%LiCl 5?F2,质量分数,%)中添加稀土Er对铸态AZ91镁合金显微组织、力学性能、断口形貌以及腐蚀行为的影响。结果表明:在熔剂中添加稀土Er能够去除镁合金熔炼过程中产生的熔剂夹杂,净化镁合金熔体,提高铸态AZ91镁合金的拉伸性能和耐腐蚀性能;当熔剂中添加10%的稀土Er时,镁合金的抗拉强度σb和伸长率δ分别从156MPa和1.8%上升到最大值220MPa和4.1%;同时,镁合金在5%NaCl水溶液中的腐蚀速率从1.20mg/(cm2.d)下降到最小值0.15mg/(cm2.d);然而,随着稀土Er在熔剂中添加量的进一步提高,合金中开始有φ-(Al7ErMn5)和τ-(Al66.7Mg23.3Er10)等含有稀土Er的相生成,消耗了合金中的Al和Mn元素,改变了β-(Mg17Al12)相的形态;而且沿枝晶界附近分布的粗大φ-(Al7ErMn5)相降低了枝晶之间的结合力,使得合金的σb和δ下降;同时,部分网状的β-(Mg17Al12)相断裂,呈离散的块状,导致合金的腐蚀速率增加;熔剂中添加稀土Er不改变镁合金的断裂机理,断裂机制仍为准解理断裂。     

原位自生Al—4Cu—0.8Mg／TiGp复合材料半固态挤压的组织与力学性能

本文对自生Al-4Cu-0.8Mg/TiCp复合材料采用T4和T6两种热处理制度，测试了该材料的σb、σs、E和δ。通过SEM观察和分析了半固态挤压原位自生Al-4Cu-0.8Mg/TiCp复合材料的显微组织和断口形貌。结果表明：在T6状态下ω（TiCp）为15％的复合材料的σb、σs、E分别达到540MPa、430MPa、92GPa,δ为3．2％，断裂形式为韧性断裂，由此可以认为自生TiCp/2024复合材料具有优良的综合力学性能。     

高低温处理条件下AZ31镁合金的力学性能与微观组织

针对月球环境温度变化情形,研究了长时间低温浸泡(-196℃)和多次高低温交变循环处理(-196～200℃)对挤压态AZ31镁合金在20℃下的力学性能、显微组织以及断口形貌的影响.研究表明:AZ31镁合金经过长时间液氮浸泡和高低温交变循环处理后,力学性能无明显变化;室温态合金的σb和δ分别为288 MPa和18.3％,经过10 d低温浸泡后σb和δ分别为292 MPa和18.7％,经过10次高低温循环后合金的σb和δ分别为294 MPa和16.9％;低温和高低温交变处理对断口形貌和相组成没有明显影响,均为准解理断裂.     

稀土Y及固溶处理对AM60镁合金组织和力学性能的影响

研究了添加少量稀土Y及固溶处理对AM60合金显微组织和室温力学性能的影响.结果表明：稀土Y的加入能显著提高合金的抗拉强度σb、屈服强度σ0.2、伸长率δ.AM60铸造合金中加入Y后,与Al形成颗粒状的稀土化合物Al2Y,使合金中的γ相Mg17Al12数量减少,合金组织得到细化.固溶处理（T4）后,γ-Mg17Al12相基本溶解,热稳定性较高的稀土化合物相未溶解,使合金的抗拉强度进一步提高.AM60-0.4%Y合金的拉伸试样断口为带有局部韧窝的解理断裂和韧性断裂的混合特征.     

ZA53镁合金的砂型铸造组织和力学性能研究

研究发现砂型铸造镁合金ZA53的主要相组成为δ-Mg基体相和τ[Mg32（Al，Zn）49]化合物相，τ相以半连续网状沿δ相晶界分布。对ZA53合金进行的固溶处理试验发现，在335℃固溶17h淬火后，合金室温抗拉强度和塑性得到大幅提高。在343℃固溶17h淬火后，合金组织完全转变为单相固溶体，合金的室温力学性能较好，σb=245MPa，伸长率为12％，合金的拉伸断口形貌由混合型断口转变为韧性断口。     

MnCl2对镁合金废旧料组织性能的影响

利用等离子发射光谱仪、金相分析、电镜、万能电子材料试验机、腐蚀试验等方法研究了含有不同量的MnCl2熔剂对镁合金废旧料的力学性能、组织、断口形貌以及腐蚀行为的影响。研究表明,MnCl2可以降低镁合金废旧料中的Fe含量,同时会增加镁合金的Mn量,使用含MnCl2的熔剂可将镁废旧料中的Fe含量降到0 0072%以下。采用含MnCl2的熔剂可以提高试样的σb和δ。当合金中的Mn量超过一定程度后,对镁合金的力学性能会产生不利的影响。金相观察表明,净化处理对断口形貌无明显的影响,不改变AZ91镁合金的断裂机理,断口均成准解理断裂。腐蚀试验表明,采用含30%MnCl2的熔剂可以使试样的腐蚀速率从20 9mg/(cm2·d)降到6 4mg/(cm2·d)。     

TiO2对镁合金废旧料组织性能的影响

利用等离子发射光谱仪、金相分析、电镜、岛津材料试验机等方法研究了含TiO2的熔剂对镁合金废旧料的力学性能、组织、断口形貌的影响。研究发现，对于AZ91镁合金废旧料，使用含TiO2的熔剂除了可以有效清除镁熔体中夹杂物外，还可将镁废旧料中的Fe含量降到0.0056%以下。试验结果表明，TiO2有助于使γ相成粒状或小岛状析出，并具有较强的细化晶粒的效果。采用含TiO2的熔剂净化处理后的AZ91镁合金废旧料的σb和δ可分别达到188.5MPa和4.13%，其性能达到了AZ91新料的水平。金相观察结果表明，净化处理对断口形貌无明显影响，不改变AZ91镁合金断裂机理，断口均成准解理断裂。     

半固态挤压原位自生Al-4Cu-0.8Mg/TiCP复合材料的组织与性能

对原位自生Al 4Cu 0 8Mg/TiCP 复合材料采用T4和T6两种热处理制度 ,测试了该材料的σb、σs、E和δ。通过SEM观察和分析了半固态挤压原位自生Al 4Cu 0 8Mg/TiCP 复合材料的显微组织和断口形貌。结果表明 ,在T6工艺处理下TiCP 含量为 15wt%的复合材料的σb、σs、E分别达到 5 40MPa、430MPa、92GPa ,δ为 3 2 % ,断裂形式为韧性断裂 ,由此可以认为 ,原位自生Al 4Cu 0 8Mg/TiCP复合材料具有优良的综合力学性能     

锑和稀土对Mg-9% Al-0.4% Zn合金铸态组织与力学性能的影响

锑和稀土均有细化Mg-9%Al-0.4%Zn合金铸态组织的作用，而且锑和稀土的同时加入，复合细化效果更显著，锑与合金中的镁元素形成短棒状的金属间化合物Mg3Sb2，稀土与合金中的铝元素形成片状金属间化合物Al11La3 和Al11Ce3。各相在a-Mg晶粒内和晶界均有分布，单独加入锑或稀土时对该合金的铸态室温力学性能基本没有影响，但同时添加0．8％RE和0．4％Sb时，合金的铸态室温力学性能显著提高，与Mg-9%Al-0.4%Zn合金相比，添加0.8%RE和0．4%Sb合金的铸态拉伸强度σb提高了33％，伸长率δ提高了70％，铸态Mg-9%AL-0.4%Zn-0.4%Sb-0.8RE拉伸断口具有明显的塑性变形特征。     

Die Wasserstoffaufnahme von Eisen bei der Korrosion in neutralen bis schwach sauren Elektrolyten

Hydrogen uptake by iron during corrosion in neutral to weakly acid electrolytes During atmospheric corrosion and corrosion by aqueous solutions, hydrogen can enter into steel. The hydrogen activity built up in iron during corrosion by dilute aqueous solutions of hydrochloric acid, sulfuric acid and iron salts has been measured as a function of pH using a permeation technique. Below pH = 5 in oxygen free solutions and pH = 4 in air saturated solutions the hydrogen activity \documentclass{article}\pagestyle{empty}\begin{document}$ a_{\rm H} {\rm = }\sqrt {{\rm p}_{{\rm H}_{\rm 2} } {\rm /(}\mathop {{\rm p}_{{\rm H}_{\rm 2} } }\limits^{\rm o} {\rm = 1}\,{\rm bar)}} $\end{document} reaches values of more than 0.1 sufficient to cause delayed cracking of steels susceptible to hydrogen embrittlement. The anions and Na⁺-ions have no markable influence. The influence of Fe³⁺ and O₂ is discussed.     

Precipitate Characteristics and Mechanical Performance of Cast Mg-6RE-1Zn-xCa-0.3Zr (x = 0 and 0.4 wt%) Alloys

In this study, the Mg-4Y-1Gd-1Nd-xCa-1Zn-0.3Zr (x = 0 and 0.4 wt%) cast alloys with low rare earth concentration were prepared in different routes of heat treatments, and their microstructures and mechanical properties were investigated. The Mg-4Y-1Gd-1Nd-1Zn-0.4Ca-0.3Zr cast alloy with ultimate tensile strength (UTS) of 264 ± 7.8 MPa, tensile yield strength (TYS) of 153 ± 1.2 MPa and elongation to failure (EL) of 17.2 ± 1.2% was successfully developed by appropriate heat treatment. The improved mechanical performance was attributed to the combined strengthening effects of fine grains, Mg₂₄RE₅, $\beta ^{\prime}$, $\beta _{1}$, $\gamma ^{\prime}$ and LPSO phases. In the heat treatment process, cooling method of T4 treatment affected the microstructure, which consequently determined the mechanical properties air cooling, rather than water cooling, gave rise to the formation of $\gamma ^{\prime}$ phase in the alloy without Ca addition. However, Ca addition facilitated the formation of $\gamma ^{\prime}$ phase, and the $\gamma ^{\prime}$ phase precipitated in the alloy after T4 treatment either by water cooling or by air cooling, but the air cooling increased the number density of $\gamma ^{\prime}$ phase in comparison to the water cooling. Although the $\gamma ^{\prime}$ phase strengthened the studied alloys, the formation of $\gamma ^{\prime}$ phase inhibited the precipitatition of $\beta ^{\prime}$ and $\beta _{1}$ phases in the following T6 treatment, and consequently reduced the strengthening effect of $\beta ^{\prime}$ and $\beta _{1}$ phases. The results showed that the mechanical performance of the studied alloys was largely determined by the precipitation of $\gamma ^{\prime}$ phase, which was regulated by the Ca addition and the cooling method of T4 treatment.     

Galvanic Corrosion of Al Alloys

In a systematic study of galvanic corrosion of Al alloys the effects of the dissimilar metal, the solution composition and area ratio have been studied using galvanic current and weight loss measurements, In 3.5% NaCl, galvanic corrosion rates of the Al alloys 1100, 20324,2219, 6061 and 7075 decrease with the nature of the dissimilar metal in the order AG>Cu> 4130 steel ?stainless steel ≈Ni>>Inconel 718?Ti-6A1-4V≈?Haynes 188>Sn>Cd. Coupling to zinc did not lead to cathodic protection of all A1 alloys. The potential difference of uncoupled dissimilar metals have been found to be a poor indication of galvanic corrosion rates. Dissolution rates of A1 alloys coupled to a given dissimilar material are higher in 3.5% NaCl than in tapwater and distilled water where they are found to be comparable. In assessing the galvanic corrosion behavior of a given A1 alloy as a function of environment, one has to consider the effect of the dissimilar metal. The dissolution rate of Al 6061 is, for example, higher in tapwater with Cu as cathode than in 3.5% NaCl with SS304L or Ti-6AI-4V as cathode. The effect of area ratio \documentclass{article}\pagestyle{empty}\begin{document}$ \frac{{A^C }}{{A^A }} $\end{document} has been studied in 3.5% NaCl for area ratios of 0.1, 1.0 or 10. The galvanic current was found to be independent of the area of the anode, but directly proportional to the area of the cathode. The galvanic current density \documentclass{article}\pagestyle{empty}\begin{document}$ i_{^g }^A $\end{document} with respect to the anode has been found to be directly proportional to the area ratio (\documentclass{article}\pagestyle{empty}\begin{document}$ \frac{{A^C }}{{A^A }} $\end{document}), while the dissolution rate r_A of the anode was related to area ratio by \documentclass{article}\pagestyle{empty}\begin{document}$ r_A = k_{_2 } (1 + \frac{{A^C }}{{A^A }}) $\end{document}. The results obtained have been explained in terms of mixed potential theory.     

Dehnungsinduzierte Korrosionsprozesse

Strain-induced corrosion phenomena When investigating stress corrosion cracking phenomena in the past, application of a static load σ played a major role in the performance of experiments. A further influencing factor, to which until now was payed less attention, is the strain ? caused by a mechanical stress. Increasing attention is payed also to the variations with time of these influencing factors, \documentclass{article}\pagestyle{empty}\begin{document}$ \dot \sigma $\end{document} and \documentclass{article}\pagestyle{empty}\begin{document}$ {\dot \varepsilon }$\end{document}. A strain, induced by a load may have the following effects: (i) break-up of a protective layer and/or (ii) mechanical stimulation of anodic metal dissolution. Both types of failures are discussed. The type of failure (i) is referred to as stress-induced, the type of failure (ii) as strain-induced corrosion. The authors discuss the question, whether type of failure (ii) is always involved in stress corrosion cracking. For some corroding systems, this question can clearly be answered in the negative, while in numerous systems the occurrence of stress corrosion cracking is markedly influenced by the strain rate. The relevant systems are described in detail. Essential for the authors' considerations is the existence of an upper and lower critical strain rate for the occurrence of stress corrosion cracking. Transition from strain-induced stress corrosion cracking to corrosion fatigue is given with relatively high upper critical strain rates. From the influence of strain rate upon stress corrosion cracking, conclusions are derived for the application of test methods for detecting susceptibility of metallic materials to stress corrosion cracking.     

Hot Deformation Behavior and Processing Maps of 0.3C-15Cr-1Mo-0.5N High Nitrogen Martensitic Stainless Steel

Hot deformation behavior of 0.3 C-15 Cr-1 Mo-0.5 N high nitrogen martensitic stainless steel(HNMSS) was investigated in the temperature range of 1173-1473 K and at strain rates of 0.001-10 s~(-1) using a Gleeble 3500 thermal-mechanical simulator.The true stress-strain curves of the studied HNMSS were measured and corrected to eliminate the effect of friction on the flow stress.The relationship between the flow stress and Zener-Hollomon parameter for the studied HNMSS wsa analyzed in the Arrhenius hyperbolic sine constitutive model by the law of Z=3.76×10~(15) sinh(0.004979σ_p)~(7.5022).The processing maps at different strains of the studied HNMSS were plotted,and its flow instability regions in hot working were also confirmed in combination with the microstructure examination.Moreover,the optimal hot deformation parameters of the studied HNMSS could be suggested at T=1303-1423 K and ε=5-10 s~(-1) or T=1273-1473 K and ε=0.005-0.04 s~(-1).     

Relationship of Ca, B, and AlP in Al–12.6Si alloy

P modification has been widely used in Al-Si piston industry, but trace of Ca element has great influence on the P modification efficiency. In this work, it is found that primary Si can be heterogeneously nucleated by AlP in near eutectic Al-12.6Si alloy, but Ca element may destroy the P modification efficiency, whereas the addition of B can recover the P modification efficiency in near eutectic Al-12.6Si alloy with high Ca containing. The microstructure transformation was related to the reaction of Ca, B, and AlP. According to the thermodynamic calculation, Ca may react with AlP and form Ca3P2 compound in Al-Si alloy, whereas, when B was added into the melt, AlP could be reformed. The reaction of Ca, B, and AlP can be shown as follows: 2AlP +3Ca→Ca3P2+2Al; Ca3P2+18B+2Al→3CaB6+2AlP. In addition, with B added into the Al-12.6Si alloy with Ca and P addition, the mechanical properties were improved compared with single Ca and/or P addition.     

Extended Hall–Petch Relationships for Yield,Cleavage and Intergranular Fracture Strengths of bcc Steel and Its Deformation and Fracture Behaviors

Extended Hall–Petch relationships for yield (\( \sigma_{y} \)), cleavage (\( \sigma_{\text{cl}} \)) and intergranular fracture (\( \sigma_{\text{ig}} ) \) strengths of pure iron have been established through the direct calculation of the proportional constant \( (k) \) and the estimation of the friction stress \( (\sigma_{0} ) \). The magnitude orders of \( k \) and \( \sigma_{0} \) are generally \( k_{y} < k_{\text{cl}} < k_{\text{ig}} \) and \( \sigma_{y0} < \sigma_{\text{cl0}} < \sigma_{\text{ig0}} \), respectively. Based on the Hall–Petch relationships, micro-yielding in a bcc steel occurs at the instance that the pile-up dislocations within a specific grain showing the Schmid factor of 0.5 propagate into the neighboring grain. The initial brittle crack is formed at the instance that the flow strength exceeds the brittle fracture strength. Once the brittle crack is formed, it grows catastrophically. Due to the smallest and \( k_{y} \) and \( \sigma_{\text{y0}} \), the cleavage and the intergranular fracture occur always after micro-yielding. The {100} cleavage fracture of the steel is due to the lowest theoretical {100} cleavage strength. Due to the thermal components included in cleavage and intergranular fracture strengths, they show also the temperature and strain rate dependence observed in yield strength. The increase in susceptibility to brittle fracture with decreasing temperature and increasing strain rate is due to the increase in dislocation density which causes the high work hardening rate.     

Mechanical and Corrosion Behavior of a Biomedical Mg-6Zn-0.5Zr Alloy Containing a Large Number of Twins

The strong texture of Mg alloys can lead to strong tension–compression yield asymmetry and corrosion anisotropy, and this will consequently affect the effectiveness of hard tissue implants. A biomedical Mg–6Zn–0.5Zr alloy containing a large number of {10$\overline{1}$2} primary twins and {10$\overline{1}$2}–{10$\overline{1}$2} secondary twins is successfully prepared by cross compression. The dual twin structure not only removes the tension–compression yield asymmetry completely, but effectively reduces the corrosion anisotropy without compromise of corrosion resistance. The difference between the largest corrosion rate and smallest one is ~ 1.2 times compared to ~ 1.6 times of the original materials. It is found that the reduced corrosion anisotropy is related to re-distribution of crystallographic orientations by twins.     

The Effect of Texture on the Corrosion Behavior of AZ31?Mg Alloy

Magnesium (Mg) grains show anisotropic corrosion behavior, which implies that the single-phase, hot-rolled Mg alloy AZ31 sheet, if highly textured, will have different corrosion performance depending on its crystallographic orientation of the grains. Its rolling surface, dominated by (0001) basal crystallographic planes, is more corrosion resistant than its cross-section surface, which is mainly composed of $ \{ 10\overline{1} 0\} $ and $ \{ 11\overline{2} 0\} $ prismatic crystallographic planes. Furthermore, grain refinement by hot rolling is beneficial to the overall corrosion resistance of AZ31 because of the dissolution of AlMn(Fe) intermetallic precipitates in the alloy. Surface compressive deformation machining can lead to refined grains and an expected preferred grain orientation, thus improving the corrosion resistance of AZ31 alloy.     

Detailed Structures and Formation Mechanisms of Well-Known Al_(10)RE_2Mn_7 Phase in Die-Cast Mg-4Al-4RE-0.3Mn Alloy

The detailed structures and the corresponding formation mechanisms of the well-known Al_(10)RE_2Mn_7 phase in the conventional die-cast Mg–4Al–4RE–0.3Mn alloy were thoroughly investigated using transmission electron microscopy(TEM). The results indicate that the Al_(10)RE_2Mn_7 phase ordinarily contains both normal (111) twins and orientation twins.Both detailed TEM observations and density functional theory calculations indicate that the Al_(10)RE_2Mn_7 phase is transferred from the Al_8REMn_4 phase following an orientation relationship as [010]_(Al_8REMn_4)//[101]_(Al_(10)RE_2Mn_7) and (101)_(Al_8REMn_4)//(110)_(Al_(10)RE_2Mn_7). Moreover, forming orientation twins in the Al_(10)RE_2Mn_7 phase is attributed to the blurry regions at incoherent twin boundaries in the Al_8REMn_4 phase. Finally, these formed orientation twins result in the (111) twins in the Al_(10)RE_2Mn_7 phase.