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…     

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％。     

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.     

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…     

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。     

Effect of Sb on microstructure and mechanical properties in Mg-10Zn-5Al high zinc magnesium alloys

In view of high strength and poor impact toughness of the high-zinc magnesium alloys,the method of micro-alloying was adopted to improve the impact-toughness of Mg-10Zn-5Al high zinc magnesium alloys by adjusting the addition of Sb.The results show that:the dystectic Mg3Sb2 particles formed by Sb and Mg are distributed in the front of dendrite,restrain the growth of the secondary phase and then change the morphology of the secondary phases,which refines the matrix in some extent and improves the impact-toug...     

La55Al25Ni20大块非晶合金对ZA27合金凝固组织的影响

将La55Al25Ni20大块非晶合金加入到ZA27合金中,研究了非晶合金对ZA27凝固组织的影响。发现加入非晶合金后的ZA27铸锭组织中析出枝晶状、块状、小花状等第二相。第二相随机分布在基体中,使基体枝晶细化。添加等量的La55Al25Ni20晶体合金时未析出小花状第二相,且对一次枝晶的细化效果不如添加非晶合金好。电子探针（EPMA）试验结果表明,析出的第二相中含有较多的Zn元素,使初生α＇相枝晶发育不完全,产生细化,且造成了麻点区的扩大。合理利用非晶独特的晶化过程,为La55Al25Ni20大块非晶在合金添加剂方面的应用开拓了新的途径。     

Influence of stacking-fault energy on high temperature creep of alpha titanium alloys

The stacking-fault energy (SFE) has been incorporated in the calculation of the steady-state creep rate of commercially-pure titanium and Ti–(1–10) mol.% Al alloys. Their creep behaviour was found to follow power-law creep when the dependence of SFE on the aluminium content was taken into account in the calculation. The possible contribution due to the formation of short range ordered structure is also discussed, with the conclusion that the decrease in SFE with increasing aluminium addition is the major factor for the strengthening effect in Ti–Al alloys.     

Sliding wear and friction behavior of ZA-27 alloy reinforced by Mn-containing intermetallic compounds

A ZA-27 alloy reinforced with M n-containing intermeta llic compounds was prepared and its tribological behaviors were investigated. By adding Mn, RE, Ti and B into ZA-27 alloy, the test alloy (ZMJ) was fabricated by sand casting. Microstructural analysis shows that considerable amount of Mn-containing intermetallic compounds such as Al5MnZn, Al9(MnZn)2 and Al65 Mn(RE)6Ti4Zn36 are formed. Compared to ZA-27, ZMJ shows better wear resistance, lower friction coefficient and lower temperature rise of worn surface under lubricated sliding condition. ZMJ also shows the lowest steady friction coefficient under dry friction condition. The wear resistance improvement of ZMJ is mainly attributed to the high hardness and good dispersion of these Mn-containing intermetallic compounds. It is indicated that the intermetallic compounds play a dominant role in reducing the sever adhesive and abrasive wear of the ZA-27 alloy.     

Microstructure and mechanical properties of ZA62 based magnesium alloys with calcium addition

As-cast microstructure and mechanical properties of Mg-6Zn-2Al-0.3Mn (ZA62) alloys with calcium addition were investigated.The as-cast microstructure of the base alloy ZA62 consists of the α-Mg matrix and eutectic phase Mg51Zn20.The Mg51Zn20 eutectic was gradually replaced by MgZn phase and Mg32(Al,Zn)49 phase when calcium is added into the base alloy.Further addition of calcium leads to the increase of grain boundary phases and formation of a new quaternary Mg-Zn-Al-Ca eutectic compound.In comparison with the base alloy,the increase of calcium addition to the base alloy results in the reduction of both strength and ductility at ambient temperature,but increase at elevated temperatures due to the thermal stability of Ca-containing phases.At elevated temperatures,the creep resistance of ZA62 based alloys containing calcium is significantly higher than that of AZ91 which is the most commonly used magnesium alloy.