Negative creep during compressive creep of as-cast ZA27 alloy

1　INTRODUCTIONAmongzinc aluminumcastalloy ,ZA2 7alloyex hibitsattractive physicalandmechanicalpropertiescombinedwithgoodfrictionandwearresistanceprop ertiesmakingitabearingalloyreplacingsomecopperalloys[1,2 ] .However ,somepropertiesofthisalloywhichmustbetakenintoaccountarecomparativelylowresistancetocreepdeformation ,poorstrengthanditsdimensionalinstabilityatmoderatelyelevatedtemperatures[35] .Thedimensionalchangesofas castZA2 7alloyonageingwerestudiedbysomework ers[1,3,6 ] ,butthesere…     

铸态ZA27合金的压蠕变行为

采用自制的实验装置研究了铸态ZA27合金在常温及高温时的压蠕变行为。在温度为20～160℃和压应力为50～137．5MPa的范围内，随温度和应力的升高，合金的压蠕变量增大，稳态蠕变速率的对数分别与应力和温度的对数曲线有较好的线性关系，稳态蠕变速率符合半经验公式。在不同的温度下，应力指数n相近，平均值为3．87；不同的应力下，表观激活能Qa相差不大，平均值为83．73kJ／mol，材料结构常数A为0．002，稳态蠕变速率由锌的点阵扩散和位错的攀移所控制。     

Effect of rare earths on phase transformation in as-cast ZA27 alloy dur-ing compressive creep

The effect of the mixed rare earths of Ce on the phase transformation in as cast ZA27 alloy during compressive creep was investigated under 37 MPa and at 160℃ by X-ray diffraction technique and SEM. The results showed that the as cast microstructure of ZA27-RE alloy consisted of a dendritic Al-rich a' surrounded by Zn-rich β' phase, interdendritic ε phase and Zn-rich η phase together with a complex Z phase which was a complex constitute compound, (RE,Cu)Al5Zn16, dispersed in crystal interfaces or branch crystal interfaces and stable during compressive creep test at 160'C. The phase transformations of ZA27-RE alloy, decomposition of β' phase and four transformation, were delayed by the addition of rare earths, also the lamellar structure and the spheroidized structure in ZA27-RE alloy were finer than in ZA27 alloy during compressive creep test at 160℃ at the same creep time, and the compressive creep resistance of ZA27-RE alloy was higher than that of ZA27 alloy.     

Superplasticity-like creep behavior of coarse grained ternary Al alloys

Enhanced tensile ductilities in coarse grained Al-Mg-Zn and Al-Mg-Fe materials were studied.The materials were Al-2Mg-5Zn,Al-3Mg-5Zn,Al-4Mg-5Zn,Al-3Mg-0.11Fe,Al-3Mg-0.27Fe,and Al-3Mg-0.40Fe.Tensile elongation-to-failure tests were conducted at constant cross-head speed and constant temperatures from 300 to 450℃.Strain rate change tests were conducted at a constant temperature from 300 to 450℃and in strain-rate range from 4.31×10-5to 1.97×10-2s-1.Experimental results show that over 100%ductilities are consistently achieved in these materials.This superplasticity-like behavior is rate-controlled by solute-drag creep.Although ternary Zn and Fe additions do not have an adverse effect on solute-drag creep and ductility,they increase stress exponent and its sensitivity to Mg content during solute-drag creep.     

Effect of Zr on behavior of compressive creep in as cast ZA27 alloy

1　INTRODUCTIONAmongzinc aluminumcastalloy ,ZA2 7alloyex hibitsattractivephysicalandmechanicalpropertiescombinedwith goodfrictionandwearresistance ,makingitabearingalloyreplacementofsomecopperalloys[1,2 ] ,alsothisalloytendstobeusedwidely .Butsomepropertiesofthisalloywhichmustbetakenintoaccountarecomparativelylowresistancetocreepde formation ,poorstrengthatmoderatelyelevatedtem peratures[35] .Additionofsomemodifyingelements ,suchasZr ,Mn ,Li,canindeedimprovetensilestrengthofthealloyatroo…     

High temperature deformation mechanism and evolution of dislocation structure during creep of Ni-Base superalloy 713LC

Creep deformation of cast nickel base superalloy 713LC has been investigated in a temperature range of 723 to 982°C. The values of the stress exponent and activation energy for creep of the alloy vary with a combination of temperature and stress. Introduction of threshold stress for creep of the alloy provided an explanation of the high values of the stress exponent and the apparent activation energy. Microstructural evolution of the alloy with creep deformation has also been studied. The analysis of the creep mechanism has been supplemented by microstructural observations after deformation under various test conditions. The dislocation structure of the alloy at high temperature and low stress was different from that at low temperature and high stress. Shearing of γ′ particles by dislocation pairs was the dominant creep mechanism at low temperature and high stress whereas dislocation climb over γ′ particles was the rate controlling process of creep at high temperature and low stress.     

铝含量对高铝锌基合金性能的影响

研究了Al≥27％的四种高Al锌基合金的组织和性能。由XRD衍射表明：高Al锌基合金的组织由α相、η相及ε相组成,随Al含量的提高,α相、η相细化,其中ZA40合金的抗拉强度及硬度最高,摩擦力矩、摩擦系数最小,在载荷800N和1100N下其耐磨性比ZA27分别提高了36．5％和69．2％。     

一种具有极高屈强比的高强钢的室温蠕变特性

利用MTS万能试验机研究了屈强比为99.7%的高强钢在不同加载应力条件下的室温蠕变行为,并对不同蠕变条件下的组织演变特征进行了分析。结果表明:在低于屈服强度的应力作用下,试验钢表现出明显的室温蠕变,且蠕变曲线呈现出以稳态阶段为主的双阶段室温蠕变特征。从蠕变曲线的拟合结果可知,曲线符合对数规律,并且蠕变速率随着蠕变时间的增加逐渐降低,其可相差两个数量级。在不同的室温蠕变条件下,该高强钢在室温蠕变过程中组织变化不明显,晶粒都以细小晶粒为主,多数为5 μm以下,且晶界都是以15°以下的小角晶界为主,而大角晶界多集中于50°~60°。     

GH4049镍基高温合金的高温蠕变行为

研究了镍基变形高温合金GH4049,在实际工作温度范围700～900℃,应力137～600 MPa下的高温拉伸蠕变行为,得到了蠕变后的高温应变恢复曲线.提出了应用参数优化估计的方法,在较大温度及应力范围内,计算稳态蠕变率的宏观唯象公式中的各参数,并用ZA27和GH4049合金的实验数据验证了该方法的可行性.GH4049合金各温度下的稳态蠕变速率与所施加的应力,在双对数坐标系下呈线性关系,应力指数平均值为7.685 1,平均稳态蠕变激活能为543.6 kJ/mol.     

锆对ZA27合金压蠕变行为的影响

采用自制的压蠕变试验装置研究了锆对ZA2 7合金压蠕变行为的影响。结果表明 ,在试验温度 2 0℃～ 1 60℃和压应力 50MPa～ 1 37 5MPa范围内 ,ZA2 7 Zr和ZA2 7合金压蠕变第一阶段的变形量和稳态蠕变速率随着温度和应力的增高而增大 ,但在 1 0 0℃以下时 ,ZA2 7 Zr合金第一阶段的蠕变量及稳态蠕变速率低于ZA2 7合金 ,合金的压蠕变抗力高于ZA2 7合金 ,在 1 60℃则相反。合金的压蠕变行为可用等式 :lnt=C -nlnσ +Q RT表达 ,其中 ,材料结构常数C不同导致两种合金的蠕变行为不同。ZA2 7 Zr合金的应力指数n和蠕变激活能Q分别为 3 63和 87 32kJ·mol-1 ,ZA2 7合金的应力指数和蠕变激活能分别为 3 46和 81 0 9kJ·mol-1 。表明Zr的加入并不影响ZA2 7合金的蠕变机制 ,均由锌的点阵自扩散和位错的攀移控制     

Fabrication of Al alloys reinforced with AlN particles formed byin-situ reaction

The tensile properties and microstructures of Al alloys reinforced with AlN particles formed byin-situ reaction under a nitrogen atmosphere were analyzed. It was found that AlN particle layers formed on the surface of the Al particles in the powder bed, which replaced the Mg₃N₂ coated layers through the reaction, Mg₃N₂+2A1 → 2AlN+3Mg. The tensile strength and 0.2% offset yield strength in the control alloys were significantly greater than those in commercial alloys. This increase was due to the fine AlN particles formed by the abovein-situ reactions of the Mg₃N₂ formation and its decomposition into AlN. This article is based on a presentation made in the symposium “The l^st KIM-JIM Joint Symposium: High Strength Ratio Aluminum Alloys”, held at Inha University, Inchon, Korea, October 22, 1999 under the auspices of The Korean Institute of Metals and Materials and The Japanese Institute of Metals.     

Effect of si addition on mechanical alloying behavior and creep properties of Al-10Ti-xSi alloys

Al-10Ti-xSi alloys (x=0∼6wt.%) have been mechanically alloyed under Ar atmosphere using an attritor and the alloying process has been investigated. From Al-10Ti composite powders, supersaturated Al(Ti) powders were obtained after mechanical alloying. In the ternary mixture, fine Si particles were observed to be distributed in the Al(Ti) matrix due to both the negligible solid solubility of Si in the Al matrix and the weaker chemical interaction of Si with Al, as compared with Ti. The sealed compacts were hot extruded to full density at 450°C with an extrusion ratio of 12:1. The microstructures and creep properties of the hot extruded alloys were examined. During consolidation, Si particles were dissolved in Al₃Ti up to 4 wt.% Si to form the (Al(Si))₃Ti phase, and the Ti₇Al₅Si₁₂ phase was formed beyond the solubility limit of Si in Al₃Ti. The transition from the Coble creep mechanism at low stresses and temperatures to dislocation one at high stresses and temperatures was observed. The stress and temperature of the transition from diffusional to dislocation creep became higher as Si concentration increased. This was due to an enhancement of Al₃Ti particle strength with increasing Si content as a result of Si incorporation. Thus, the addition of Si enhances the creep resistance of the MA Al-10Ti alloy.     

Mg-Al-Nd/Sr耐热镁合金的组织结构与蠕变性能

以Mg-6Al合金为基体,分别单一添加稀土Nd、Sr和复合添加稀土Nd和碱土Sr元素,采用水冷模工艺制备Mg-6Al-6Nd,Mg-6Al-2Sr和Mg-6Al-2Sr-2Nd耐热镁合金,并比较研究单一添加Nd或Sr和复合添加稀土Nd和碱土Sr对合金组织结构和蠕变性能的影响。结果表明:复合添加稀土Nd和碱土Sr后,合金中除了析出第二相Al2Nd、Al11Nd3和Al4Sr外,还析出Sr和Nd相互取代的Al4(Sr,Nd)和Al11(Nd,Sr)3复合相;在Mg-6Al-2Sr基础上添加2%Nd,不仅细化合金枝晶间距,还显著地提高第二相的分布密度,增强合金蠕变过程中位错与第二相交互作用,提高合金的蠕变性能。     

Mechanical properties and creep resistance of Mg-Li composites reinforced by MgO/Mg_2Si particles

1　ＩＮＴＲＯＤＵＣＴＩＯＮＭｇ Ｌｉａｌｌｏｙｉｓａｎｅｗａｎｄｓｕｐｅｒ ｌｉｇｈｔｓｔｒｕｃｔｕｒａｌｍａ ｔｅｒｉａｌ.Ｉｔｉｓｗｉｄｅｌｙｕｓｅｄｉｎｓｐａｃｅａｎｄｗｅａｐｏｎｉｎｄｕｓｔｒｙｂｅｃａｕｓｅｏｆｈｉｇｈｅｒｓｐｅｃｉｆｉｃｓｔｒｅｎｇｔｈａｎｄｒｉｇｉｄｉｔｙ .Ｓｏｍｅｒｅｓｅａｒｃｈ[1～8] ｉｎｄｉｃａｔｅｄｔｈａｔ:1 )ｔｈｅｓｔｒｅｎｇｔｈｏｆｂｉｎａｒｙａｌｌｏｙｉｓｌｏｗｅｒａｎｄｔｈｅｃｒｅｅｐｒｅｓｉｓｔａｎｃｅｉｓｖｅｒｙｐｏｏｒ;2 )ｔｈｅｓｔｒｅｎｇｔｈｃａ…     

Melting characteristics of magnesium—lithium alloys

Mg-Li-Al alloys containing 4–14 wt% Li and 1.5 wt% Al have been prepared by melting Mg/Mg-Al master alloy and Li separately under MgCl2 + KCl + MgO + CaF₂ and LiCl + LiF flux covers, respectively, and mixing the two together. The observed lithium loss and the pick-up of impurity elements in the melt have been correlated with various physico-chemical phenomena occurring during melting. The effect of holding time on melt composition was also examined. The results indicate that it is possible to control the alloy composition within specified limits by the selection of proper melting fluxes and crucible materials and by restricting the holding time to the minimum possible. These findings suggest that flux-cover melting is a viable route for the production of sound cast ingots of highly reactive magnesium—lithium alloys.     

Damage mechanisms in the particle reinforced aluminum alloy 6061 under creep loading

The creep behaviour of the particle reinforced aluminium alloy 6061 is investigated using experimental and numerical techniques. In order to describe the influence of ceramic particles on the overall creep curve of the composite an idealised unit cell model with a periodic arrangement of particles is generated. The particles are assumed to react linear elastically. Particle cleavage is taken into account. For the matrix an additive viscosity hardening law coupled with an isotropic damage variable is used. The results show that the fracture time is strongly influenced by the presence of particles. Qualitative good agreement with experimental data is found.     

不同Si/Al比和变质处理对ZA27合金中Si相形态的影响

分析了Al-Si合金中初生Si相的变化规律，并与相同Si／Al比的ZA27合金中析出的Si相作比较，提出了将Al-Si合金中对Si相的变质工艺应用到ZA27合金中，细化组织中的Si相。结果表明，在ZA27合金中Si相的变化规律与Al-Si合金中的Si相大致相同，用1．5％的Cu-P中间合金对ZA27合金进行变质处理，可获得良好的变质效果。     

Al2O3P/ZA27复合材料的高温摩擦磨损特性

借助SRV高温摩擦磨损试验机、SEM及能谱分析仪研究了Al2 O3p/ZA2 7复合材料的高温摩擦磨损特性。结果表明 :在边界润滑条件下 ,Al2 O3p/ZA2 7复合材料的高温磨损质量损失较ZA2 7合金降低 0 .0 0 5 34g ;摩擦因数随着增强颗粒体积分数的增加而降低 ,当增强颗粒的体积分数由 10 %增加到 30 %时 ,Al2 O3p/ZA2 7复合材料的摩擦因数由 0 .142降低到 0 .132 ,但均高于ZA2 7合金。其高温失效形式为犁削和疲劳磨损。     

离心铸造ZA27合金铝偏析的控制

研究了不同工艺因素和添加剂的加入对离心铸造ＺＡ２７合金中铝的偏析的影响。结果表明，浇注温度、浇注速度和重力倍数对偏析有明显影响，加入锰和稀土能有效地抑制铝的偏析。