Effect of cold rolling on properties and microstructures of dispersion strengthened copper alloys

Mechanical properties and microstructures of unidirectionally and tandem rolled alumina dispersion strengthened copper（ADSC） alloys under different conditions were investigated by tensile test, optical microscopy（OM）, transmission electron microscopy（TEM） and scanning electron microscopy（SEM）. For unidirectionally rolled ADSC alloys, their strengths and elongations in the longitudinal direction are higher than those in the transverse direction under both cold rolling and annealing conditions. Once fracture appears in their longitudinal stress--strain curves, sudden reduction of overall stress level before complete fracture can be observed in the transverse tensile curves. The anisotropy of mechanical properties for the ADSC alloy can be greatly improved by tandem cold rolling. And no sudden reduction of overall stress level appears in the stress--strain curves for tandem rolled ADSC alloys. The differences of their microstructures and tensile fractures were analyzed. In order to compare the differences of tensile fracture mechanism in different directions, longitudinal and transverse fracture models for unidirectionally rolled ADSC alloys were also introduced.     

Effects of heat treatment on microstructure and mechanical properties of Mg-8Gd-3Y-0.5Zr(wt.%)alloy fabricated by semi-continuous casting

The microstucture,mechanical properties and fracture behaviors of semi-continuous cast Mg-8Gd-3Y-0.5Zr(wt.%,GW83K) alloy after different heat treatments were investigated.Almost all the eutectic compounds were dissolved into the matrix and there was no evident grain growth after optimum solution treatment at 500 ℃for 4h.Further ageing at low temperatures led to significant precipitation hardening,which strengthened the alloy.Peak-aged at 200 ℃,the alloy had the highest ultimate tensile strength(UTS) and lowest elongation at 395 MPa and 2.8%,respectively.When aged at 225 ℃ for 15 h,the alloy exhibited prominent mechanical performance with UTS and elongation of 363 MPa and 5.8%,respectively.With regard to microstructure and tensile properties,the processes of 500 ℃,4h+225℃,15 h are selected as the optimal heat treatment conditions.The alloy under different conditions shows different fracture behaviors:in the as-cast alloy,a quasi-cleavage pattern is observed;after solution treatment,the alloy exhibits a trans-granular quasi-cleavage fracture;after being peak-aged at 200 ℃ and 225 ℃,the fracture mode is a mixed mode of trans-granular and intergranular fracture,in which the inter-granular mode is dominant in the alloy peak-aged at 200 ℃.     

Influence of Al-Ti-B addition on the microstructure and mechanical properties of A356 alloys

The mechanical properties (σb,σ0.2,and δ) and fracture behavior of tensile specimens of the refined A356 alloys were investigated as a function of the addition level of Al-Ti-B master alloy under both as-cast and T6 heat-treated conditions. The results show that as the addition level of Al-5Ti-1B master alloy increases from 0.1 wt.% to 5.0 wt.%,the mechanical properties of refined A356 alloys improve steadily and then decrease slightly under both as-cast and T6 heat-treated conditions. Also,they display exc...     

Effect of cold-rolling on tensile strength of SiCw/Al composite

SiCw/Al composite was fabricated through a squeeze cast route and cold rolled to about 30%, 50% and 70% re-duction in thickness, respectively. The length of whiskers in the composite before and after rolling was examined using SEM. Some of the rolled composites were recrystallization annealed to remove the work hardening of matrix alloy. The tensile strength of the rolled and annealed SiCw/Al composites was examined and then associated with the change of the whisker length and the work hardening of matrix alloy. It was found that the tensile strength is a function of the degree of cold rolling. For the cold rolled composites, with the increase in the degree of cold rolling, the tensile strength increases at first, and decreases when the degree of cold rolling exceeds 50%. For the annealed ones, however, the tensile strength de-creases monotonously with the increase in rolling degree. The different changes in tensile strength between the rolled and annealed composites could be attributed to the result of     

Tensile behavior of Ti-6Al-4V alloy fabricated by selective laser melting: effects of microstructures and as-built surface quality

Selective laser melting(SLM) is a powerful additive manufacturing(AM) technology, of which the most prominent advantage is the ability to produce components with a complex geometry. The service performances of the SLM-processed components depend on the microstructure and surface quality. In this work, the microstructures, mechanical properties, and fracture behaviors of SLM-processed Ti-6 Al-4 V alloy under machined and as-built surfaces after annealing treatments and hot isostatic pressing(HIP) were investigated. The microstructures were analyzed by optical microscope(OM), scanning electron microscope(SEM) and transmission electron microscopy(TEM). The mechanical properties were measured by tensile testing at room temperature. The results indicate that the as-deposited microstructures are characterized by columnar grains and fine brittle martensite and the asdeposited properties present high strength, low ductility and obvious anisotropy. After annealing at 800-900°C for 2-4 h and HIP at 920°C/100 MPa for 2 h, the brittle martensite could be transformed into ductile lamellar(α+β) microstructure and the static tensile properties of SLM-processed Ti-6 Al-4 V alloys in the machined condition could be comparable to that of wrought materials. Even after HIP treatment, the as-built surfaces could decrease the ductility and reduction of area of SLM-processed Ti-6 Al-4 V alloys to 9.2% and 20%, respectively. The crack initiation could occur at the columnar grain boundaries or at the as-built surfaces. The lamellar(α+β) microstructures and columnar grains could hinder or distort the crack propagation path during tensile tests.     

Effect of deformed microstructure on mechanical properties of Ti-22Al-25Nb alloy

Effect of the deformed microstructure on mechanical properties of an orthorhombic （Ti2klNb） based alloy of Ti-22Al-25Nb （mole fraction, %） has been investigated. It was found that the deformed microstructures in different portions of a flee forged rod with diameter of 30 mm were quite different and thus resulted in the different mechanical properties after the same subsequent heat-treatment. One deformed microstructure with less primary α2/O particles and a larger and equiaxed B2 grains resulted in poor RT ductility, but the other one with a relatively larger amount of the primary α/O particles and non-equiaxed B2 grains had good combination of the tensile strength and ductility both at RT and 650 ℃. It was also found that two different deformed microstructures were obtained for the hot rolling plates with thickness of 3 mm even processed under an identical nominal rolling and the same post-deforming heat treatment conditions. One only has 3.5% of RT tensile elongation and the other up to 8%.     

Mechanical Properties and Microstructural Evolution of Bulk UFG Al 2014 Alloy Processed Through Cryorolling and Warm Rolling

Tensile properties,microstructural evolution and fracture toughness of A1 2014 alloy subjected to cryorolling followed by warm rolling(CR + WR)have been investigated in the present study.The solution-treated(ST)A1 2014 alloy is cryorolled followed by warm rolling process at different temperatures(110,170 and 210 ℃).The mechanical properties and microstructural features of deformed and undeformed A1 2014 alloys were characterised by optical microscopy,transmission electron microscopy(TEM)and scanning electron microscopy(SEM).The CR + WR samples at 170 ℃ showed an improved hardness(179 HV),tensile(UTS 499 MPa,YS 457 MPa)and fracture toughness(K_Q= 37.49 MPa m~(1/2),K_(ee) = 37.39 MPa m~(1/2) and J integral= 33.25 kJ/mm~2)with respect to ST alloy as measured from the tensile and fracture toughness test.The improved mechanical properties of CR + WR alloy are attributed to grain boundary strengthening,combined recovery and recrystallisation,precipitation hardening and dynamic ageing effect during the deformation.The precipitation of metastable spherical phase Al_2Cu was responsible for the improved tensile and fracture properties of finegrained A1 2014 alloy observed in the present work.     

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℃.     

Effect of rolling and heat treatment on microstructure and properties of Ti-26 sheet

The effect of heat treatment and rolling process on the properties and microstructures of Ti-26 （Ti-15V-3Al-3Cr-3Sn-Forming） sheet was studied. The results show that the best rolling temperature for Ti-26 alloy is in the temperature range from 900 ℃ to 950℃. Under this condition, the resistance of deformation and yield ratio are low and the alloy has better hot work ability. The alloy will achieve better mechanical properties and completely recrystallized β microstructure when the deformation ratio is not less than 60% and the solution temperature is 30 ℃ above the phase transformation temperature. The best heat treatment conditions are recommended as： 790℃, 30 min, AC or WQ followed by 510 ℃, 10 h, AC. Under this heat treatment condition the strength of the Ti-26 alloy is 1 230 MPa and the elongation is 15%.     

Inhomogeneity of microstructure and mechanical properties of a 500 mm diameter heavy section semi-continuous cast AZ61 magnesium alloy ingot简

For the large magnesium alloy ingot, there is a considerable difference in cooling rate of different parts in the ingot, which leads to non-uniform distribution of the secondary phases, solute segregation and tensile properties. In the present research, an heavy AZ61 alloy ingot with a diameter of 500 mm was made by semi-continuous casting. The microstructure and mechanical properties at different positions along the radial direction of the large ingot were investigated by using an optical microscope(OM), a scanning electron microscope(SEM), an energy dispersive spectroscope(EDS), and a micro-hardness tester. The results indicate that the microstructure of the AZ61 ingot is non-uniform in different locations. It changes from equiaxed to columnar grains from the center to the edge; the average grain size gradually reduces from 1,005 μm to 763 μm, the secondary dendrite arm spacing reduces from 78 μm to 50 μm, and the Mg17(Al,Zn)12 phase is also refined. The micro-hardness value increases from 55.4 HV at the center to 72.5 HV at the edge of the ingot due to the microstructure differences, and the distribution of micro-hardness at the edge of the ingot is more uniform than that in the center. The tensile properties at room temperature show little difference from the center to the edge of the ingot except that the elongation at the edge is only 3.5%, much lower than that at other areas. The fracture mechanism is ductile fracture at the center and cleavage fracture at the edge of the ingot, and at the 1/2 radius of the ingot, a mixture of ductile and cleavage fracture is present.     

Al-Si过共晶钎料的制备及其对核用SiC陶瓷的焊接研究

SiC是核聚变反应堆流道插件及结构材料的优秀候选材料。为了获得大尺寸的SiC部件,通过钎焊方法连接SiC,选择50Al-50Si合金作为钎料,研究50Al-50Si合金钎料的显微组织、力学性能及在真空1100℃×10min条件下对SiC陶瓷的钎焊性能。并在此钎料基体上加入不同含量(2%,6%,10%,14%)的Ti,研究Ti的加入对钎料显微组织性能及SiC陶瓷接头力学性能的影响。结果表明,Al-Si-Ti钎料能完成SiC陶瓷的连接而获得性能优异的接头。在Ti含量增加到6%时,接头剪切强度升高至138.98MPa,随着Ti含量增多,接头剪切强度又下降。     

Formation of Fe-19 wt%Cr-9 wt%Ni Nanocrystalline Alloy with Excellent Corrosion Resistance: Phase Transition and Microstructure

In this paper, microstructure characteristics and phase transitions of Fe-19 wt%Cr-9 wt%Ni nanocrystalline alloy are comprehensively studied during the mechanical alloying and hot pressing sintering processes. Corrosion resistance of the sintered Fe-19 wt%Cr-9 wt%Ni nanocrystalline alloy samples is further analyzed. During the mechanical alloying process, Fe-19 wt%Cr-9 wt%Ni nanocrystalline alloy powders mainly composed of metastable ferrite phase are obtained after mechanical alloying for 8, 16 and 24 h, respectively. In the subsequent hot pressing sintering process, the phase transitions(from ferrite to austenite) occur from 650 to 750 °C for Fe-19 wt%Cr-9 wt%Ni alloy powders milled for 24 h. When the sintering temperature is raised to 1050 °C for 1 h, the ferrite phase has transformed into austenite phase completely, and the obtained grain size of sintered Fe-19 wt%Cr-9 wt%Ni alloy is around 40 nm. Electrochemistry test of the sintered Fe-19 wt%Cr-9 wt%Ni alloy has been operated in 0.5 mol L~(-1) H_2SO_4 solution to show the corrosion resistance properties. Results show that the sintered Fe-19 wt%Cr-9 wt%Ni alloy exhibits excellent corrosion resistance, which is proved by higher self-corrosion potential, lower self-corrosion current density and larger capacitive reactance, compared with that of commercial 304 stainless steel.     

Dynamic Precipitation of Laves Phase and Grain Boundary Features in Warm Deformed FeCrAl Alloy:Effect of Zr

Warm compression deformation of Fe-13.5％Cr-4.7％Al-2.0％Mo-0.70％Nb-0.40Ta (wt％) (FeCrAl) and Fe-13.5％Cr-4.7％Al-2.0％Mo-0.45％Nb-0.40Ta-0.11Zr (wt％) (FeCrAl-Zr) ferritic stainless steel was performed by a thermal simulation machine Gleeble 3800 at 600 ℃ and strain rates of 0.01-10 s-1.Before deformation,all the samples were solution-annealed for 2 h at 1150 ℃ for FeCrAl alloy and 1250 ℃ for FeCrAl-Zr alloy.The strain rate has little or no effect on peak stress,and the precipitates in matrix or grain boundary precipitates (GBPs) have no difference in the samples deformed at the strain rate 0.01 s-1 and 1 s-1 both in FeCrAl and FeCrAl-Zr alloys.The addition of Zr increased the proportion of low-angle grain boundaries (LAGBs).The Laves phase in FeCrAl alloy precipitated uniform in the matrix,while in FeCrAl-Zr alloy Laves phase precipitated at grain boundary and formed GBP.The LAGBs and ∑3 coincident site lattice (CSL) grain boundary both increased in FeCrAl-Zr alloy,which possessed some beneficial properties such as high-temperature creep resistance to the Fe-Cr-Al alloy.More interesting,twins were created by warm deformation,which was difficult in typical bcc ferrite alloy.These results could be expected to provide guidance for subsequent warm working processes for the alloy.     

Influencing factors on as-cast and heat treated 400-18 ductile iron grade characteristics

As-cast and heat-treated 400-18 ductile iron (DI) grade was obtained in different foundry conditions, as metallic charge, Mg-treatment alloy and inoculation. It was found that the Pearlitic Influence Factor (Px) and Antinodulizing Complex Factor (K1) have an important influence on property of DI, depending on the Mn and P level, the metallurgical quality of iron melt, rare earth (RE) and inoculation. It was also found that the influence of Mn is depended on the phosphorus and residual elements level in ductile iron. Less than 0.03％P and 0.2％Mn and Px＜2.0 are the basic conditions to obtain as-cast ferritic structure. At the same lower level of Mn and P, the increasing of residual elements (Px＞2.0) determines presence of pearlite in as-cast structure, while ferrite structure is obtained after a short annealing heat treatment. Lower level of phosphorus (P＜0.025％) and residual elements (Px＜2.0) allow to use relative high Mn content (0.32％-0.38％), in condition of ferritic structure, including in as-cast state. High P (0.04％-0.045％) and Mn (0.25％-0.35％) content stabilized pearlite, especially at lower level of residual elements (Px ＜2.0). Antinodulizing action of elements was counteracted up to K1=2.0 level, by RE included in Mg-treatment alloy, which are beneficial for K1＜1.2 and compulsory for K1＞1.2. Si has a significant influence on the mechanical properties of heat treated ductile irons an important decreasing of elongation level and a moderate increasing of yield and tensile strength and their ratio in 150-170 HB typical hardness field. A typical final chemical composition for as-cast 400-18 ductile iron could include 3.5％-3.7％C, 2.4％-2.5％Si, max.0.18％Mn, max.0.025％P, max.0.01％S, 0.04％-0.05％Mgres.for Px＜1.5 and K1＜1.1. High purity pig iron, RE-bearing FeSiMg and powerful inoculant are also recommended.     

轴向冲头和移动推块共同进给成形三通管新工艺

运用ABAQUS显式算法模拟仿真轴向位移变量和内压变量对成形支管的高度、最大和最小壁厚的影响,分析壁厚分布情况,探究支管补料原理。模拟仿真结果表明:在一定位移变量和内压变量范围内,大位移量和高内压对增加支管高度的贡献率分别为330%和84.2%,对最大壁厚值的影响分别为39.4%和13.5%,对最小壁厚值的影响分别为5.1%和33.8%;双侧移动型成形工艺的支管壁厚呈现出两侧对称的4个峰值和3个谷值分布规律;移动推块和轴向挤压冲头的补料原理是将两端的管料推挤送进到支管根部实现补料过程。     

不锈钢CMT焊接对装配间隙及错边的适应性研究

使用CMT(Cold Metal Transfer,冷金属过渡焊接技术)焊接方法对2 mm厚度的X2CrNiN18-7不锈钢焊接过程中间隙和错边的适应性进行研究。在板厚2 mm的情况下,CMT焊接对焊缝间隙容忍力强,达到母材厚度的37.5%;磨平处理的焊缝抗拉强度可达到母材的80%~88%;对焊缝错边量容忍力可达到母材厚度的40%。     

轧制压下量对Fe-8Al合金板材耐蚀性的影响

采用真空电磁感应熔炼制备了Fe-8Al合金,采用80%、70%、63%和50%轧制压下量制成合金板材,最后对4种Fe-8Al合金板材进行900℃退火保温10min后水冷的热处理。采用扫描电子显微镜(SEM),拉伸试验和电化学试验对4种Fe-8Al合金板材的性能进行分析。结果表明:随着轧制压下量的增大,Fe-8Al合金板的晶粒尺寸逐渐减小;轧制压下量为80%时Fe-8Al合金板材的综合力学性能最好;轧制压下量为63%时Fe-8Al合金在5%(质量分数)Na2SO4溶液中的耐蚀性最好。80%为Fe-8Al合金轧制工艺制度的最佳轧制压下量。     

添加剂对鳞片石墨在水介质中分散性能的影响

以鳞片石墨在水介质中的沉降率和分散率作为评价指标,研究了7种添加剂单独以及复合添加对鳞片石墨在水介质中分散性能的影响。结果表明:十二烷基苯磺酸钠和十二烷基硫酸钠对石墨在液相中的分散效果显著,分散率分别为97.8%和80.0%,0.5h时的沉降率分别为92.0%和94.0%,但稳定性不好;通过正交试验方法得出最佳添加剂配方,即十二烷基硫酸钠添加量为4.7%(质量分数,下同),N-乙酰-L-脯氨酸添加量为3.7%和磷酸三丁酯添加量为2.6%,按该最佳配方添加时鳞片石墨在水介质中的分散率达到99.2%,1h时的沉降率为92.0%;在用最佳配方制备的银-石墨复合镀层中,鳞片石墨已被均匀分散在银层中。     

Effect of reclaimed sand additions on mechanical properties and fracture behavior of furan no-bake resin sand

In this work,the effects of reclaimed sand additions on the microstructure characteristics,mechanical properties and fracture behavior of furan no-bake resin sand have been investigated systematically within the temperature range from 25 to 600 ℃.The addition of 20％-100％ reclaimed sand showed dramatic strength deterioration effect at the same temperature,which is associated with the formation of bonding bridges.Both the ultimate tensile strength (UTS) and compressive strength (CS) of the moulding sand initially increase with the increase of temperature,and then sharply decrease with the further increase of temperature,which is attributed to the thermal decomposition of furan resin.The addition amount of reclaimed sand has a remarkable effect on the room temperature fracture mode,i.e.,with the addition of 0-20％ reclaimed sand,the fracture mode was mainly cohesive fracture;the fracture mode converts to be mixture fracture mode as the addition of reclaimed sand increases to 35％-70％;further increasing the addition to 100％ results in the fracture mode of typical adhesive fracture.The fracture surface of the bonding bridge changes from a semblance of cotton or holes to smooth with the increase of test temperature.     

基于最优化理论自卸车液压举升机构优化设计分析

液压举升机构是自卸车重要组成部分,也是衡量整车性能的主要部件之一,其结构和性能对整车寿命和安全具有重要影响。根据液压举升机构的结构特点和性能特征,运用最优化理论,利用MATLAB建立自卸车液压举升系统数学模型并进行优化分析,运用ADAMS搭建液压系统及举升机构分析模型。以举升缸容量、举升力为优化设计目标,以举升缸铰接点位置为设计变量,考虑边界约束、不干涉性约束、举升缸安装长度约束、最高油压约束等4个约束条件,对机构进行优化分析。搭建液压举升机构试验台进行试验分析,对最优化设计进行验证。分析结果可知:举升缸安装长度和最大行程分别减少6.4%和4.0%,最大举升力和容量分别降低3.6%和6.97%,同时举升时间缩短7.26%,第一级和第二级缸径相对减小6.5%和7.7%。容量减少和缸径减小有利于流量减小、油泵等的选型和整车布置,研究方法和结论为实际设计生产提供参考。