Effect of Roughness and Surface Hardening on the Mechanical Properties of Three-Layered Brass/IF Steel/Brass Composite

In this research, three-layered brass/IF steel/brass composite produced by cold roll bonding (CRB) process was investigated. The effect of roughness and surface hardening of each layer on the mechanical properties of three-layered composite were separately examined. For this purpose, five rotatory wire brush models were used in order to prepare the surfaces for CRB process. The peeling and shear punch tests were also used to evaluate the mechanical properties of samples. Finally, optical and scanning electron microscopes were used to evaluate the fracture surfaces. The chemical compositions were analyzed at the joint interface by an energy dispersive X-ray analysis. It was observed that, decreasing the diameter of the brush enhanced the roughness and surface hardening. However, the increase in roughness and surface hardening of brass were less than that of IF steel due to different wear mechanisms. The results showed that, at the same reduction, the bond and shear strengths of composite were enhanced by increasing the surface roughness of each layer. Also, increasing the brass surface roughness had more effect on the bond strength of the strips due to its vital role in bonding formation in CRB processing. Moreover, rising the surface roughness of IF steel in comparison to brass had more influence on the shear strength of the composite.     

颗粒尺寸对真空浸渗SiC/Al复合材料性能的影响

采用无压浸渗法制备了SiC/Al复合材料,考察了复合材料中SiC颗粒尺寸对复合材料的组织结构、抗弯强度、摩擦磨损性能的影响.结果表明:随着SiC颗粒尺寸的减小,SiC/Al复合材料的残余气孔率逐渐减小,密度和抗弯强度逐渐增加;粒度配比有利于提高复合材料的抗弯强度.与灰铸铁配副时,材料的摩擦系数与磨损率明显依赖于碳化硅颗粒尺寸,二者均随颗粒尺寸的增大而先降低后增大.粒度配比能明显改善复合材料的干摩擦磨损性能.粗细颗粒的粒度配比具有相互强化的作用,有利于降低摩擦系数和磨损率,并使其趋于稳定.     

连退工艺对Nb+B-IF钢显微组织与性能的影响

以Nb+B-IF钢为研究对象,对其连续退火工艺进行了模拟试验,运用光学显微镜和透射电镜分析技术对不同加热速率细晶高强IF钢显微组织进行了研究。结果表明,随着加热速率提高,饼状铁素体数量增多,晶粒尺寸逐渐增大,屈服强度、抗拉强度和r值升高,n值降低,无沉淀析出区体积分数增大,形状更加稳定。     

Si-Ti-B掺杂金刚石/硬质合金复合体的性能

金刚石粒度和掺杂量两因素对Si-Ti-B掺杂金刚石/硬质合金复合体的金刚石层的抗弯强度和耐磨性的综合影响,可以归结为平均自由程与机械性能的关系。在强度(或耐磨性)与平均自由程的关系曲线中,存在最大值。对于低掺杂量材料,强度随平均自由程(粘结相层厚度)的减少而降低。对于高掺杂量材料,强度随粘结相层厚度的增大而下降。Si-Ti-B掺杂烧结金刚石的耐热性高于钴粘结金刚石。     

Microalloyed,vacuum degassed high-strength steels with special emphasis on IF steels

In comparison with other high-strength concepts, high-strength IF steel has a particularly high forming capacity with increased strength, while the sheet thickness reduction through forming is, on the whole, smallest with high-strength IF steel. Solid-solution hardening through Si, Mn and P is particularly suitable as a mechanism for increasing strength, as this leads to comparatively low formability losses with increased strength values. An additional increase in strength is possible using the bake-hardening effect. This can be achieved with an incomplete C and N binding through Ti and/or Nb, or through stoichiometric microalloying with V. The effect is basically caused by the relatively low thermodynamic stability of VC. V-alloyed, vacuum degassed steel combines in this way good forming behaviour with an increase in strength through bake-hardening. Through an increasing segregation of P at grain boundaries, solid solution hardening with this element can lead to unfavourable embrittlement in higher strength IF steel and to intercrystalline fracture. B-addition to the amount of 0.002% (mass content) greatly reduces the tendency to become brittle without leading to any remarkable losses with regard to formability. Examinations concerning the precipitation behaviour of Ti-IF steel with P show that a formation of iron titanium phosphate (FeTiP) in the hot strip only occurs where there is an excess of Ti and high coiling temperatures are used. For a P-alloyed IF steel with stoichlometrical Ti-content no precipitation of FeTiP takes place in hot band, nor is the thermal activation in continuous annealing simulation sufficient to achieve a transformation of existing Ti-precipitates into FeTiP, which might occur according to literature.     

Intercritical Rolling Induced Ultrafine Lamellar Structure and Enhanced Mechanical Properties ofMedium-Mn Steel

The medium-Mn steel with ferrite and austenite structure was rolled in the intercritical region down to dif- ferent rolling reduction. The microstructure and mechanical properties of the rolled steels were investigated by scan- ning electron microscopy, transmission electron microscopy, X-ray diffraction and tensile tests. It was found that the ferrite and austenite structure gradually evolved into an ultrafine structure from the random directional lath structure to lamellar structure with lath longitudinal direction parallel to the rolling direction with increasing rolling strain. It was found that the thickness of the laths was gradually refined with increasing rolling strain. The lath thickness is about 0. 15 9m stored with high density dislocations and the austenite volume fraction of the steel is about 24% after 80% rolling reduction. Furthermore, it was interesting to find that yield strength, tensile strength and total elongation of the 80% rolled medium-Mn steel are about 1000 MPa, 1250 MPa and 24%, respectively, demonstrating an excellent combination of the strength and ductility. Based on the microstructure examination, it was proposed that the grain refinement of the medium-Mn steels could be attributed to the duplex structure and the low rolling temperature. Analysis of the relationship between the microstructure and the mechanical properties indicated that the high yield strength mainly resulted from the ultrafine grain size and the high density dislocation, but the improved ductili- ty may be attributed to the large fractions of austenite retained after intercritical rolling.     

卷取温度对Ti微合金化高强钢力学性能的影响机理

固定化学成分和其他工艺参数,研究了紧凑式带钢生产卷取温度变化(625和579℃对Ti微合金化高强钢组织和力学性能的影响。热轧带钢的力学性能测试表明,卷取温度降低后,屈服强度降低205 MPa,而-20℃冲击功由11.7J增加到47 J。采用光学金相、电子显微术等手段分析了钢中组织和析出物,625℃卷取带钢为铁素体组织,579℃卷取带钢组织更为细小,贝氏体特征明显;而卷取温度降低后纳米尺寸碳化物的数量显著减少,由此降低了沉淀强化效果,造成强度大幅下降,并与组织细化一起改善材料的韧性。卷取温度是Ti微合金化高强钢生产中重要的工艺参数,需要严格控制。     

Strengthening of composites due to microstructural changes in the matrix

The addition of discontinuous silicon carbide (SiC) to aluminum (Al) alloys can result in a five-fold increase in the yield stress. The magnitude of the increase is obviously a function of the volume fraction and the particle size of the SiC. Previously, it was proposed that the strength increase due to SiC addition to Al alloys was the result of change in the matrix strength, i.e. an increase in dislocation density and a reduction of subgrain size. The data obtained from a series of experiments indicate that dislocation density increases with an increase in volume fraction of SiC and decreases with an increase in particle size. The subgrain size decreases as the volume fraction increases and increases as the particle size increases. There is a good correlation between the microstructural changes in the matrix and the changes in the yield stress of the composites.     

Preparation of SiC Nano-particulates Reinforced Aluminum Matrix Nanocomposites by High Intensity Ultrasonic Cavitation Process

The present investigation attempts to evaluate the effect of high intensity ultrasonic cavitation on dispersing the SiC nanoparticles in aluminum 6061 melt. Aluminum melt with various volume percentages of SiC nanoparticles was ultrasonically processed by dipping the ultrasonic horn into the melt. SEM and EDS study with elemental mapping validates the uniform distribution of SiC nanoparticles in the Al matrix. Compared to the un-reinforced alloy matrix and conventional composites, the mechanical properties of the nanocomposites, including tensile strength and hardness improved quite significantly as the particle volume percentage increased. The nanocomposites show better ductile properties as compared to the conventional composites. To understand the effect of ultrasonic vibrations on processing the nanocomposites, the nanocomposite was processed at three amplitudes and the results are presented. Ultrasonic cavitation based fabrication process proved as a better alternative to the conventional stir casting route to disperse the nano ceramic particles in molten alloys.     

Study of Tribological and Mechanical Properties of A356–Nano SiC Composites

In the present investigation, the microstructural, wear, tensile and compressive properties of Al?C7Si alloy matrix nano composites have been discussed. It is noted that the composites contain higher porosity level in comparison to the matrix and increasing amount of porosity is observed with the increasing volume fraction of the reinforcement phase in the matrix. The wear sliding test disclosed that the wear resistance of the nano SiC reinforced composites is higher than that of the unreinforced alloy. It is believed that the presence of SiC particles could shield the matrix and silicon phase from directly experiencing the applied load from the counterface. It was revealed that the presence of nano-SiC reinforcement also enhanced the hardness, tensile and compressive yield strength of Al?C7Si alloy which can be attributed to small particle size and good distribution of the SiC particles and grain refinement of the matrix. The highest yield strength and UTS was obtained by the composite with 3.5?vol% SiC nano-particles. The results show that the addition of nano-particles reduces the elongation of A356 alloy.     

Influence of annealing pattern on microstructure and mechanical property of low carbon Al- killed steel

Comparison was conducted about the influence of annealing patterns on the microstructure, mechanical property and natural aging property of Al- killed steel with carbon content range between 0. 04 mass% to 0. 06 mass% by optical observation and uniaxial tensile testing. The results show that the product with batch annealing process exhibits lower strength, higher elongation and better formability property. The strength increases with the increase of the strip thickness while the elongation shows a decreasing tendency. Yield strength ratio has different relation to thickness for both strips. The final product with continuous annealing shows apparent sensitivity to coiling temperature. And ferrite grain size increases with increasing coiling temperature. Furthermore, batch annealed sheet enjoys better natural anti- aging property which can be guaranteed within six months.     

水雾化不锈钢粉末注射成形坯的溶剂脱脂技术

采用多组元聚合物蜡基粘结剂体系,进行水雾化316L不锈钢粉注射成形,研究溶剂脱脂温度、粉末装载量、试样厚度、粉末粒度等工艺参数对溶剂脱脂率的影响.结果表明,脱脂温度越高、粉末装载量越低、试样厚度越薄、粉末粒度越小,则粘结剂脱除率越大.文中首先分析讨论了脱脂可能的速率控制步骤,再通过实验结果对速率控制步骤进行判定,认为脱...     

Microstructure and Mechanical Properties of Ultrafine-Grained Interstitial-Free Steel Processed by ECAP

Equal-channel angular pressing (ECAP) of interstitial-free (IF) steel at equivalent strain, ε_vm = 12 has been employed to develop ultrafine-grained (UFG) microstructure with high fraction of low angle grain boundaries, that enhances strength significantly with reduced tensile ductility. ECAPed IF steel has been deformed further by cold rolling/cryorolling at ?50 °C to >90 % reduction in area. It is observed that the UFG structure gets refined with an improvement in high angle grain boundary fraction and heavily stressed non-equilibrium grain boundaries in cryorolled state resulting in significant strengthening. However, the decrease in grain size to an ultrafine level with the increased lattice strain lowers the work hardening ability of the material that limits its ductility. Hence, the rolled samples are flash annealed at 675 °C in order to recover the ductility of the material by achieving partially recrystallized structures. Consequently, the increased subgrain size as well as the grain size, the reduced residual lattice strain, lower hardness and strength with marginal recovery of ductility is maintained in order to attain the yield strength 2–3 times compared to that of as-received coarse-grained IF steel.     

三价铬超声-脉冲电沉积Fe-Ni-Cr/SiC纳米复合镀层

利用超声-脉冲复合电沉积法,在三价铬镀液体系中,添加羧酸盐-尿素配合剂和SiC纳米颗粒,制备了Fe-Ni-Cr/SiC纳米复合镀层.研究了超声-脉冲工艺参数与SiC纳米粒子复合量、Cr含量及镀层厚度的关系;利用稳态极化曲线和循环伏安法分析了超声波对阴极电化学行为的影响.结果表明,超声-脉冲作用均有利于基质金属Fe、Ni和Cr的电沉积,提高了镀层中SiC和Cr的含量以及镀层的厚度.利用扫描电镜、X射线衍射仪和能谱仪对Fe-Ni-Cr/SiC纳米复合镀层的表面形貌、微观结构和组成等进行表征,发现采用该技术可制备厚度为23.56μm,SiC和Cr质量分数分别为4.1%和25.1%的Fe-Ni-Cr/SiC纳米复合镀层.磨损量和腐蚀曲线测试结果表明,SiC含量高的复合镀层,其耐磨性和耐蚀性更好.     

Effect of Cold Rolling Parameters on Bond Strength of Ti Particle Embedded Al Strips

Bond strength of cold roll bonded Al layers with and without Ti particles was studied. The effect of particle’s content that was placed between aluminium sheets and rolling reduction on weld efficiency and bonding was studied. Peel test was used to measure the adhesive strength between the bonded Al strips. The weld efficiency \(\eta\) of the roll bonding process was calculated. The results showed that the weld efficiency in the presence of Ti is lower than that in the absence of Ti. The surface conditions of the peeled surfaces were inspected by scanning electron microscopy. It could be concluded that by enhancing the rolling reduction up to 70%, the bonded area on the interface is increased and bonds with higher strength are produced. However, the addition of Ti particles leads to reduction of the bonded area and bond strength. Also, presence of Ti powders up to 0.5 wt%, lead to the increase of threshold deformation to 45%.     

Effect of reinforcement volume fraction on mechanical alloying of Al–SiC nanocomposite powders

Abstract

Mixtures of aluminium powder and nanoscaled SiC particles (n-SiC) at various volume fractions of 0, 1, 3, 5, 7 and 10 are comilled in a high energy planetary ball mill under an argon atmosphere to produce nanocrystalline Al–SiC nanocomposites. High resolution scanning electron microscopy (HRSEM), X-ray diffraction (XRD) method, laser particle size analysis and powder density measurement were used to study the morphological changes and microstructural evolution occurred during mechanical alloying. Al–SiC composite powder with microscaled SiC particles (1 m m) was also synthesised and characterised to examine the influence of reinforcement particle size on the milling process. It was found that with increasing volume fraction of n-SiC, a finer composite powder with more uniform particle size distribution is obtained. The morphology of the particles also became more equiaxed at shorter milling times. Furthermore, the analysis of XRD patterns by Williamson–Hall method indicated that the crystallite size of the aluminium matrix decreases with increasing reinforcement volume content while the lattice strain changes marginally. As compared with microscaled SiC particles, it appeared that the effect of n-SiC on the milling stages is more pronounced. The results clearly show that the reinforcement particles influence the work hardening and fracture of the metal matrix upon milling, affecting the structural evolution. With decreasing size of the ceramic particles to nanoscale, this influence becomes more pronounced as the surface to volume fraction increases.     

稀土对高强IF钢退火过程中的第二相析出行为的影响

以不同稀土含量的440 MPa高强IF钢为研究对象,在盐浴炉中模拟现场的连续退火,退火温度810℃,分别保温30 s、60 s,通过TEM与XRD对退火后的试样进行第二相分布、形状及成分分析,以研究稀土对高强IF钢第二相析出行为的影响。实验结果表明,保温时间基本不影响第二相的析出;不加稀土的高强IF钢析出的第二相呈弥散分布,且尺寸大小均匀,均在30 nm以下;加了稀土的高强IF钢析出的第二相分布在晶界处,并且伴随着团聚的现象,第二相尺寸不均匀,大颗粒在30 nm^100 nm之间;不加稀土的试验钢在810℃保温60 s下的析出相种类有FeTiP、TiC、TiN、NbN。实验结果为440 MPa高强IF钢在退火条件下第二相析出奠定了理论基础。     

Investigation on Precipitation Hardening High Strength IF Steel Sheet for Automotive Application

High strength IF steel sheets with sufficient formability had been extensively used in automotive industry.In this paper,a new type of high strength cold-rolled IF steel with higher carbon and niobium contents was studied.Thermal plastic and continuous annealing were performed on thermo-mechanical simulator.The transformation points were tested by thermal expansion apparatus.Optical microscopy and transmission election microscope (TEM) were used to analyze the microstructure and the secondary precipitates of the steel.The results showed,the ductibility temperature range was from 950℃ to 1250℃ and the transformation points were 887℃ and 913℃ respectively.The grain size of this steel was smaller than that of conventional high strength IF steel.At the mean time,there were many fine Nb(C,N) precipitates distributed in the intra-granular regions and the PFZ (precipitate free zone) were formed in the neighborhood of grain boundaries.Due to the unique micro-structural feature,the yield strength and the yield ratio of the steel were decreased while the tensile strength was increased.With the increasing of the annealing temperature,the strength decreased,the total elongation A50,r-value at 15% strain and n-value were all increased.In order to obtain the favorable mechanical properties,the skin-pass rolling rate should be chosen at 0.6-0.8%.     

Inclusion and its deformation behavior in 304 stainless steel

Non-metallic inclusion is the main reason for the presence of surface defects in cold-rolled steel strip. In this study,the composition,morphology,and size of the non-metallic inclusion in hot-rolled 304 stainless steel strips are analyzed. Cold-rolled 304 stainless steel strips with different cold-rolling reduction have been prepared,and the morphology and size of inclusion in these cold-rolled strips are also analyzed. Furthermore,the deformation behavior of a non-metallic inclusion during the cold-rolling process is studied. The results showthat Ca O-SiO2-MgO-Al2O3,a kind of brittle compound oxide,is the main type of inclusion in hot-rolled 304 stainless steel strips.During the cold-rolling process,ductile deformation of this type of inclusion is not obvious,where large inclusions are crushed,and the average size of inclusions in cold-rolled strips decreased while the cold-rolling reduction increased.     

Effect of overaging and particle size on tensile deformation and fracture of particle-reinforced aluminum matrix composites

The effect of reinforcement particle size and overaging treatment on the tensile behavior and fracture morphology of a 2080/SiC/20 _p composite was investigated. Tensile behavior was profoundly influenced by particle size and matrix strength. The composite strength increased with a decrease in particle size, while overaging greatly reduced the strength of the composite, independent of particle size. Almost all particles on the fracture plane were fractured, and the amount of particle fracture in the composites was insensitive to overaging and particle size, due to the excellent bonding between SiC particles and the Al matrix. Fractography showed that void nucleation in the matrix of peak-aged composites took place primarily at very fine SiC particles, which were much smaller than the average SiC particle size. Subsequent failure took place by the tearing topography surface (TTS) mechanism. In the overaged composite, composites failed by a more conventional void nucleation and growth process, where void nucleation took place at coarsened S precipitate particles, resulting in smaller and more elongated voids.