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Abstract Copper (Cu) foils are extensively used in the electronics industry owing to their excellent electrical conductivity and high flexibility. In the present study, Cu foils with a thickness of 100 µm were annealed at 700 °C for 3, 6, 30 and 60 min to obtain different grain sizes. The edge cracking of Cu foils in micro rolling was systematically investigated, and the mechanism involved was discussed combining the effects of grain size and tensile properties. The results of tensile tests show that the tensile curves become increasingly discrete with the increase of grain size. Both the fracture stress and the fracture strain decrease, and the scatter of stress increases with the coarsening of grains. The tensile fracture surfaces of the specimens with grain sizes of 19 and 23 µm contain very few micro-dimples, while no micro-dimples are formed on the fracture surfaces of the tensile tested specimens with grain sizes of 33 and 43 µm. The results of micro rolling tests show that edge cracking does not generate in the specimens with grain sizes of 19 and 23 µm after micro rolling. However, the edge becomes increasingly wavy with the increase of grain size and rolling reduction. When the grain size is increased to 33 µm or greater, significant edge cracking occurs under all the rolling reductions of 30%, 51% and 70%. Grain size has a significant effect on the edge cracking of Cu foils in micro rolling, which evolves based on the ductile fracture mechanism. [ABSTRACT FROM AUTHOR]

Currently, it is widely acknowledged that ridging is caused by different plastic deformations from grains with different textures. In this study, a simplified model was used to predict the ridging height with different elongation values based on crystal plasticity (CP) and EBSD information with the purpose of understanding well the effect of texture and average grain size on the ridging generation and reduction of undesirable surface defects of ferritic stainless steel (FSS) 430 during the formation process. The results indicate that the reduction of average grain is effective to improve ridging generation in FSS along tensile directions. The numerical simulation results obtained using the crystal plasticity finite element model (CPFEM) match well with experimental values, which demonstrates that the CPFEM could be employed to analyse the ridging phenomenon under different elongation conditions of FSS. Based on the established models, the ridging modes of colonies with different crystal orientations ({001} <110>, {112} <110> and {114} <110>) are discussed to evaluate the effect of texture structure on ridging generation. [ABSTRACT FROM AUTHOR]

Abstract: In the present work, the effects of tungsten (W) addition and heat treatment conditions on the microstructure, impact toughness and tensile properties of microalloyed forging steels were studied. Four kinds of microalloyed forging steels were produced by varying W additions (0, 0.5, 1 and 2wt%). Heat treatment was carried out at temperatures ranging from 840 to 950°C followed by air and furnace cooling. Mechanical tests were used to evaluate the room temperature Charpy impact and tensile properties. The resulting microstructures were analysed via optical microscope (OM), scanning electron microscope (SEM) and transmission electron microscope (TEM). The results show that the microstructure and mechanical properties of the microalloyed forging steels are closely related to the W content. Correct selection of heat treatment temperature and cooling method is very important to enhance the mechanical properties. The optimum heat treatment temperatures obtained in this study are 920, 900, 880 and 860°C for the steels with 0%, 0.5%, 1% and 2% W, respectively. Both the impact toughness and tensile properties of the microalloyed forging steels have been significantly enhanced after heat treatment at the optimum temperatures followed by air cooling. [Copyright &y& Elsevier]

Abstract: In the present work, detailed studies were made on the optimization of microstructure and mechanical properties of a low-carbon microalloyed cast steel through control of heat treatment conditions. Specimens were austenitized at temperatures ranging from 950 to 1200°C for 2h followed by different cooling methods (furnace, air and water). For analyzing the effect of holding time on mechanical properties, some cast specimens were austenitized at 1100°C for different times followed by furnace cooling. After heat treatment, mechanical tests were employed to evaluate the room temperature Charpy impact and tensile properties. The characterization of complex precipitates formed during heat treatment process was investigated by using analytical electron microscopy. The results show that dissolution of vanadium-containing precipitates plays an important role in the abnormal growth of austenite grains at 1150°C. Further growth in austenite grains at 1200°C is caused by the dissolution of Ti-containing particles and the reduction of the amount of precipitates. Correct selection of the austenitizing temperature, holding time and cooling method is very important to improve the mechanical properties of the steel. Heat treatment at 1100°C for 2h followed by furnace cooling leads to the best combination of excellent Charpy impact and tensile properties. [Copyright &y& Elsevier]

The interfacial morphologies play a crucial role in mechanical properties of laminated/bimetal composite. This study investigates the effects of heat treatments on the interfacial characteristics, mechanical properties and fracture behaviour of a 2205 duplex stainless steel/AH36 carbon steel bimetal composite with varying interface situations fabricated by the hot-rolling and subsequent heat treatments. The bimetal composite was annealed from 850 °C to 1150 °C in steps of 100 °C with soaking 1 h. Heterogeneities of grain size and element concentration exist in the microstructural evolution of bonding zone adjacent to interface after annealing treatments, which were observed by the optical microscope and scanning electron microscope (SEM) coupled with the energy dispersive X-ray spectroscopy (EDS). It was found that the diffusion transition zone of Cr and Fe alloy elements between component 2205 and AH36 steel layers present an increasing trend with the rise of annealing temperature. The results of conventional, shear and compact tensile test indicate that the tensile strength of 2205/AH36 bimetal composite gradually decreases but the fracture elongation increases with the rising annealing temperature, the thicker alloy element diffusion zone results in the stronger interfacial shear strength and better ductility of bimetal composite, but the thick and strong interface has less positive effect than the mechanical properties of bimetal composite itself on preventing the fatigue crack growth across the interface. [ABSTRACT FROM AUTHOR]

High temperature low cycle fatigue tests at various strain amplitudes (±0.5%, ±0.6%, ±0.8%, ±1.0%) and strain rates (0.5%/s, 0.05%/s, 0.005%/s) were performed at 550 °C. The stress decomposition method and microstructure characterization were used to analyze cyclic hardening and softening behavior. Results showed that increased back stress and the combined action of back and friction stresses were responsible for the pronounced cyclic hardening at the early and late stages of initial hardening, respectively. The decrease in friction stress resulted in cyclic softening until final fracture. Moreover, the evolution behavior of dynamic strain aging (DSA) activity was discussed, which showed a clear dependence on loading cycles and directions. Specifically, the DSA activity was firstly attenuated and then gradually intensified from the late stage of cyclic hardening, and it was stronger in the compressive plastic deformation regime of hysteresis loops than in the tension part. • The increase in intergranular back stress and friction stress causes cyclic hardening. •The decrease in friction stress contributes to the cyclic stress softening. •The DSA activity attenuates firstly and then gets enhanced during cyclic loading. •The DSA activity under compression loading is stronger than that under tension part. [ABSTRACT FROM AUTHOR]

Abstract Stir tools with different pin eccentricities were applied to the friction stir processing of Al-5052 alloy. Results show that pin eccentricity enhances material flow and refines grains of stir zone. The stir zone produced by a stir tool with 0.4 mm pin eccentricity performs the highest hardness and yield strength, attributing to the enhanced grain-boundary strengthening. [ABSTRACT FROM AUTHOR]

2 mm thick Al-7B04 alloy sheets under T6, T4 and O tempers were subjected to friction stir processing (FSP). The microstructure, Vickers hardness and tensile properties of the stir zone were characterized. The results show that the initial base metal temper has a significant impact on the microstructure and the mechanical properties of the stir zone. FSP led to the formation of full recrystallized microstructure, the average grain size in the stir zone ranged from 2.1 to 2.2 μm when the base metal tempers were T6 and T4. On account of the relatively strong pin force of the precipitates, the grains in the stir zone became finer when O temper base metal was applied. Besides, the stir zones produced using the base metal under T6 and T4 tempers were softened, while a significant strengthening was observed when the base metal temper was O. The softening in the stir zone for T6 and T4 temper is attributed to the dissolution of fine strengthening precipitates during FSP, and the strengthening for O temper arises from the grain refinement caused by FSP. [ABSTRACT FROM AUTHOR]

Samples with one through three passes with 100% overlap were created using friction stir processing (FSP) in order to locally modify the microstructure and mechanical properties of a cold-rolled Al-5083 alloy. A constant traverse speed and two different rotational speeds were used for processing. The results indicated that single-pass FSP caused dynamic recrystallization in the stir zone, leading to equiaxed grains with high angle grain boundaries. The grain size increased with increasing the rotational speed. The product of ultimate tensile strength and total elongation of the stir zone was significantly enhanced compared with that of the base metal. During the annealing heat treatment, abnormal grain growth (AGG) occurred throughout the stir zone when a low rotational speed was adopted. The stir zone produced with a high rotational speed was found to be more resistant to AGG. The application of multiple process passes did not change the grain size and mechanical properties of the stir zone significantly. The expanding of AGG in the stir zone was inhibited as the number of passes was increased. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, the strain hardening behaviors of a low carbon Nb-microalloyed Si–Mn quenching–partitioning (Q–P) steel were investigated. The microstructures were analyzed by the scanning electron microscope (SEM) and transmission electron microscope (TEM). Mechanical tests were used to evaluate the room temperature tensile properties of the steel. The work hardening behaviors of the tested specimens were analyzed using the Hollomon approach. The results showed that a two-stage work hardening behavior was observed during deformation processes. In the first stage, for the quenched samples, martensite deforms plastically and the hardening exponent decreased. For the air-cooled samples, however, the carbide-free ferrite deforms preferentially, and then, the carbide-free ferrite and martensite co-deform. In the second stage, due to the effect of transformation induced plasticity of retained austenite, the hardening exponent decreased slowly and plateaus were observed in the plots of n i –ε t until fracture. Variations of the work hardening behaviors were related to the martensite and the volume fraction of retained austenite in Q–P steels and the microstructural evolution during partitioning and following cooling process. [Copyright &y& Elsevier]