Fatigue behaviour of commercially pure aluminium processed by rotary swaging

Fatigue strength of ultrafine-grained commercially pure aluminium (Al 1050) produced by severe plastic deformation (rotary swaging) was investigated. Fatigue tests were carried out on smooth and notched specimens. Results show improved static and fatigue strength of the rotary swaging processed material. However, the processed material was highly notch sensitive due to low work hardening capability, low ductility as well as low uniform strain. It was found that post-deformation annealing above recrystallization temperature can additionally enhance the work hardening capability and the ductility of the swaged material, which led to marked reduction in fatigue notch sensitivity. At the same time, this reduction is accompanied with pronounced loss in strength. Fatigue notch sensitivity of commercially pure aluminium can be good correlated to the work hardening capability and ductility. This behaviour was discussed in details based on microstructure and mechanical properties study.     

Microstructures and mechanical properties of pure Mg processed by rotary swaging

Microstructures and tensile properties of commercial pure magnesium processed by rotary swaging (RS) technique were investigated. Bulk and gradient textures in the RS processed Mg were characterised by neutron and synchrotron diffractions, respectively. Grains of the pure Mg were gradually refined with increase in the RS passes, which largely contributed to an increase in the tensile yield strength. A dominated basal fibre texture was observed in the RS processed pure Mg. Accommodated twinning deformation was also observed. Both the optical observations and texture analyses through the diameter of the swaged rod showed a gradient evolution in microstructure.     

交流伺服直驱式旋锻机的动力学理论研究

提出了高速伺服直驱式旋锻机结构,分析设计了基于摆线运动曲线的锤头轮廓曲线,采用上限法确定了旋锻机在极限工况下的最大输出载荷上限的变化规律。研究表明,随着进料角的增大,锻机负载有所降低,但同时工件需要更大的推进力,因此实际中采用的进料角的范围为5°-15°。     

Novel microstructures from severely deformed Al–Ti alloys created by chip formation in machining

We present some consequences of Severe Plastic Deformation (SPD) of Al–Ti alloys by chip formation in machining that can enable opportunities for creating novel microstructures. Chips cut from Al-6wt%Ti are composed of a refined dispersion of the fragmented remains of a hitherto coarse Al₃Ti embedded in a nanostructured matrix. This multi-phase nanostructured chip material demonstrates considerable resistance to coarsening owing to the thermally stable dispersion of ultra-fine Al₃Ti dispersions and thus has promise in structural alloy applications. Furthermore, the Al–Ti machining chips are shown to possess excellent grain refining characteristics, leading to microstructurally refined and homogeneous Al alloy castings. This realization enables a low-cost route for enhancing the efficiency of the grain refiner master alloy systems by exploiting SPD during chip formation.     

Work softening and work hardening during rotary swaging of copper

Abstract

Cold–worked and annealed copper rods were deformed at room temperature in a four–die rotary swaging machine. The outer parts of the cold–worked rods were work softened, whereas the annealed rods were inhomogeneously work-hardened, with a strength increase from the surface to the core. Both effects can be explained as being a consequence of a cyclic deformation during rotary swaging.

MST/148     

Microstructure and mechanical properties of Mg–Al–Zn alloy sheets severely deformed by accumulative roll-bonding

The as-rolled AZ31 Mg alloy sheets were subjected to accumulative roll-bonding (ARB) at 300 °C up to three cycles. The microstructure and macro- texture are investigated by means of optical microscopy and X-ray analysis. The mechanical properties are evaluated by micro-hardness and tensile tests. Very fine grain size of 2.4 μm could be achieved after three passes of 50% thickness reduction. The recrystallized structure was already formed after one cycle of ARB. ARB processing resulted in a significant increase of ductility and slight decrease of tensile strength of the AZ31 alloy sheet. Basal texture was notably weakened after ARB processing.     

LYP1050轮转胶印机控制系统设计

In order to meet the demand of printing market for high-speed, high-quality and highefficiency offset presses, a LYP1050 rotary offset press control system is designed. Firstly, taking the Inovance AC810 motion controller as the main controller and the Inovance IT6000 series touch screen as the human-computer interaction interface, the hardware platform of the LYP1050 rotary offset press control system was built by combining the servo drive unit. Then, the methods including the multi-axis synchronization control, the tension control of closed-loop speed and winding taper and the automatic registration control for the LYP1050 rotary offset press were proposed;at the same time, the lower computer program and human-computer interaction interface of the LYP1050 rotary offset press control system were designed. Finally, the reliability of the designed control system was verified by collecting the registration error of the LYP1050 rotary offset press prototype during actual operation. The test results showed that the registration accuracy of this rotary offset press could be controlled within ±0.05 mm, which met the registration requirements. The designed control system is safe and reliable, with good synchronization, high color registration accuracy, low failure rate, and wide versatility, which can provide references for the design of the similar rotary offset press control system. © 2021. All rights reserved.     

Microstructure of a recycled AA7050 alloy processed by spray forming followed by hot extrusion and rotary swaging

The aim of this study is to evaluate the microstructure of a recycled AA7050 alloy processed by spray forming followed by hot extrusion and swaging. Machining chips from an aircraft manufacturer were used as raw material. The microstructure was investigated by optical microscopy (MO) and scanning electronic microscopy (SEM). The spray formed deposit was homogenized at 743 K, 8 h, extruded at 693 K with a deformation rate of 0.1 s^–1 and an extrusion rate of 156:1, producing a bar with 8.0 mm in diameter. Due to a specific combination of high extrusion temperature and deformation rate, partial recrystallization occurred and different grain sizes were obtained through the extruded cross section. After extrusion, the 8.0 mm bar was processed by rotary swaging in several steps up to a 2.0 mm final diameter. The resulting microstructure revealed a cold worked structure, with no recrystallization. Tensile tests were performed in both cases and the slant type of fracture reveals that Portevin Le‐Chatelier effect took place in this alloy. Moreover, the efficacy of extrusion and rotary swaging parameters to reduce the porosity, intrinsic to the spray form process, was analyzed, as well the distribution of intermetallic particles.     

Characterisation of severely deformed austenitic stainless steel wire

Abstract

The microstructure of 8 μm diameter wire produced by the severe deformation of 316L austenitic stainless steel has been examined using TEM and X-ray diffraction. The deformation imparted amounts to a true strain of 6·3. Data from previous studies on strain induced transformation of this steel have been combined with new results to show that true strains >2 are required in order to observe mechanical stabilisation, i.e. the cessation of martensitic transformation when the martensite/austenite interfaces are unable to propagate through the dislocation debris created in the austenite.     

Microstructural evolution of bainitic steel severely deformed by equal channel angular pressing

High Si bainitic steel has been received much of interest because of combined ultra high strength, good ductility along with high wear resistance. In this study a high Si bainitic steel (Fe-0.22C-2.0Si-3.0Mn) was used with a proper microstructure which could endure severe plastic deformation. In order to study the effect of severe plastic deformation on the microstructure and properties of bainitic steel, Equal Channel Angular Pressing was performed in two passes at room temperature. Optical, SEM and TEM microscopies were used to examine the microstructure of specimens before and after Equal Channel Angular Pressing processing. X-ray diffraction was used to measure retained austenite after austempering and Equal Channel Angular Pressing processing. It can be seen that retained austenite picks had removed after Equal Channel Angular Pressing which could attributed to the transformation of austenite to martensite during severe plastic deformation. Enhancement of hardness values by number of Equal Channel Angular Pressing confirms this idea.     

微小型轴向内沟槽铜管缩径缺陷实验研究

二分模旋转模锻工艺是微小型轴向内沟槽铜管(AIGCT)的重要缩径工艺.本文通过实验探讨了两种不同截面尺寸类型(分别记作Ⅰ和Ⅱ)和三种不同的材料属性状态(分别记作:A、B和C)下沟槽管缩径缺陷和缩径进给速率的关系.实验结果表明,A状态Ⅰ型管的伸长率最高可达到20%以上,并随着进给速率的增加而减小;当进给速率超过21mm/s时,在A状态Ⅰ型管的成形区将会产生飞边;当进给速率超过13mm/s时,在A状态Ⅱ型管的成形区将产生凹陷.进给速率超过4mm/s和13mm/s时,将分别会在B状态Ⅰ型管和Ⅱ型管的未成形区产生扭曲.由于存在严重的扭曲和压溃,C状态内沟槽铜管不适合用二分模的方式进行缩径.     

Corrosion behaviour of silicon carbide particle reinforced 6061/Al alloy composites

The corrosion behaviour of 6061 Al alloy-SiC_p composites (in as cast and extruded form) have been studied in sea water and acid media. The effects of temperature of both the media and concentration of the acid medium were also investigated. The corrosion behaviour was evaluated using electrochemical technique and corroded specimens were examined using scanning electron microscopy. The studies revealed that corrosion damage of composites exposed to sea water medium was mainly localized in contrast to uniform corrosion observed for base alloy. Further, composites were found to corrode faster than the base alloy even though the attack was mainly confined to the interface, resulting in crevices or pits. This could be attributed to the presence of thin layer of reaction product present at the interface acting as an effective cathode which when continuous would increase the cathode to anode ratio enabling higher localized corrosion. However, the extent of corrosion damage in extruded composites was less possibly due to absence of defects like gas pores in the composites and homogeneity in the distribution of particles. Increase in temperature invariably increased the attack for all the materials studied. This is explained due to the metal dissolution (anodic process) which is governed by the kinetics at that temperature.     

Plasma nitriding of steels with severely plastic deformed surfaces

Linear Flow Splitting (LFS) is a new massive forming process, which enables the continuous production of integral bifurcated profiles with ultrafine-grained surface layers. Owing to the uniaxial material flow during LFS, the grains in the ultrafine-grained (UFG)-layer are highly elongated with minimum grain dimensions perpendicular to the split surface. With increasing distance to the split surface, the UFG-microstructure changes into a conventionally strain-hardened microstructure. The microstructural gradient is accompanied by a gradient in hardness and strength with maximum values at the split surface in the UFG-layer. Further improvement of hardness and wear resistance can be achieved by nitriding. In spite of their low thermal stability, earlier investigations demonstrated that nitriding of UFG-microstructures is feasible even at elevated temperatures like 500 °C. But, as most publications are referred to equiaxed grains, it is unclear whether the results can be transferred to LFS-profiles with their highly elongated grains. Whether pancake UFG-microstructures are still beneficial for plasma nitriding is the subject of this work. For this, the microstructure of a linear flow split micro-alloyed HSLA steel is characterized after nitriding and subsequent heat treatment by EBSD and SEM measurements. Mechanical properties are examined by hardness indentations. It is shown that nitriding of pancake-shaped UFG-microstructures is still beneficial in terms of higher compound layer thickness and hardness compared to a strain-hardened microstructure. Moreover, nitriding reduces the grain growth, i.e. stabilizes the UFG-microstructure.     

Microstructure and mechanical properties of commercial purity titanium severely deformed by ARB process

Commercial purity titanium was deformed by accumulative roll-bonding (ARB) process up to 8 cycles (equivalent strain of 6.4) at ambient temperature. This is the first study on ultra-high straining of h.c.p. metals by the ARB process. The microstructure of the ARB-processed specimens showed two kinds of characteristic ultrafine microstructures. One was the lamellar boundary structure elongated along RD, which has been also reported in the ARB-processed cubic metals. The lamellar boundary spacing decreased with increasing ARB strain and reached about 80 nm after 5 ARB cycles. The other microstructure was the equiaxed grains having mean grain size of 80–100 nm. Such a fine and equiaxed grain structure has not yet been reported in the as-ARB-processed materials before. The fraction of the equiaxed grains increased as the ARB process proceeded, and 90% of the specimen was filled with the equiaxed grains after 8 ARB cycles. As the number of the ARB process increased, the tensile strength increased and the total elongation decreased gradually. After 6 ARB cycles, the specimen exhibited almost the same mechanical properties as that of commercial Ti-6Al-4V alloy.     

Stored energy of a severely deformed interstitial free steel

A Ti-stabilised IF steel subjected to room temperature equal channel angular pressing (ECAP) for 8 passes, route B_C was further cold rolled to 25, 50 and 95% thickness reductions. The evolution of bulk stored energy (350–600 J mol⁻¹) and the associated thermal behaviour was investigated by differential scanning calorimetry (DSC). Local stored energy (5–140 J mol⁻¹) was measured using microhardness, electron back-scattering diffraction (EBSD) and X-ray line profile analysis. The higher stored energy values via calorimetry correspond to energy release from all sources of strain in the material volume as well as Ti precipitation during annealing. An apparent activation energy of 500–550 J mol⁻¹ suggests sluggish recrystallisation due to excess Ti in solid solution.     

Quantification of the recrystallization behaviour in Al-alloy AA1050

A new methodology for the determination of the recrystallized volume fraction from anodically etched aluminium alloys using optical microscopy is described. The method involves the creation of a composite image from multiple micrographs taken at a series of orientations. The results of quantitative analysis of images obtained by this new method are compared with those obtained using the traditional single image optical microscopy technique, orientation imaging microscopy (OIM) and microhardness indentation. The multiple orientation image method is shown to consistently yield a recrystallized volume fraction which is significantly higher than that determined from a single image while multiple orientation imaging and OIM results are found to be in good agreement. Furthermore it is shown that, after the subtraction of the effect of concurrent recovery using the rule of mixtures, microhardness indentation can also be used to determine the recrystallized volume fraction.     

Effects of Si addition on mechanical properties of copper severely deformed by accumulative roll-bonding

Effects of Si addition on mechanical properties of severely deformed copper by accumulative roll-bonding (ARB) have been investigated. Tensile tests and strain-rate jump tests have been carried out at room temperature. For annealed coarse-grained polycrystals, the difference in yield stress σ _0.2 between pure copper and a Cu–1.64at.%Si alloy was only about 15 MPa while the difference became 170 MPa after the ARB process by six cycles. The strain-rate sensitivity m of pure copper increased with increasing the number N of the ARB cycles for N ≥ 5. However, the increase in m becomes less significant for Cu–Si alloys. These findings have been discussed in terms of thermally activated dislocation processes.