查看更多>>摘要：Ironing that achieved by reducing the clearance between forming tools have been proved to be able to generate high collar, regular geometry and good formability in conventional flanging process. In this paper, the effect of ironing on flanging characteristics during the Lorentz-force-driven (LFD) hole flanging process were investigated with the use of 5182 aluminum alloy. The ironing phenomenon in the LFD flanging process were realized by decreasing the diameter of die and keeping the punch diameter constant. To reveal the formation mechanism with or without ironing in this high-speed process, the elastoplastic finite element simulation model was established. Typical features in the final profiles, including junction ridge, spring-back, tip inclination, that determined by three critical clearance-thickness ratios (R-cc1, R-cc2 and R-cc3) were analyzed. Especially, the evolution of spring-back and tip inclination with respect to the varying clearance-thickness ratios (R-c) were discussed in details. According to three Rcc values, ironing identification and ironing extents (mix-ironing and pureironing) separation could be achieved at the same time. Based on the analysis of radius, wall and tip in the flanged part, a height calculation method was proposed for the replacement of simulation in flanging cases with Rc lowered than R-cc2. The comparison with experimental heights proved the feasibility of prediction formula.
查看更多>>摘要：Cutting force and surface finish are two critical characteristic parameters for diamond turned polycrystalline copper components. In this work, polycrystalline copper with different grain sizes achieved by friction stir processing (FSP) was machined by single point diamond turning. To accurately predict cutting force in diamond turning, a theoretical prediction model considering grain size of copper, Hall-Petch effect, and stress distribution on a diamond tool was developed. Three-direction cutting forces, i.e., principal cutting force, thrust force, and feed force, in the diamond turning process were calculated, respectively. To analyse the material microstructure and mechanical property, Electron Back Scattered Diffraction (EBSD), X-Ray Diffraction (XRD) and nanoindentation analysis were successively performed on the work material. Combing theoretical model and experimental results, the relationship between principal cutting force and thrust force on various processing parameters was successfully revealed. Furthermore, surface roughness of the copper work material processed by FSP is smaller than that without treatment. According to material analysis results, the combination of misorientation angle and Hall-Petch effect reduces the step height on diamond turned surface, which further contributes to a flatter diamond turned surface. Therefore, the combination of friction stir processing and single point diamond turning has the application potential to achieve a super-smooth surface finish in industry.
查看更多>>摘要：The twin-roll casting (TRC) process is typically used to fabricate laminated metal cladding strips with rectangular cross-sections, and it has the advantages of short flow, low energy consumption, green environmental protection, etc. Recently, a twin-roll solid-liquid cast-rolling bonding (TRSLCRB) process was proposed based on the TRC process to fabricate metal cladding materials with round cross-sections. However, the nonuniformity of heat transfer and mass transfer along the circumferential direction finally influences the performance uniformity. Therefore, a multi-roll solid-liquid cast-rolling bonding (MRSLCRB) process was proposed integrating cast-rolling bonding technology and multi-roll groove rolling technology. The steady-state thermal resistance network was established, and the influences of nominal roll radius, groove radius, and molten pool height on the heat transfer and mass transfer were studied systematically. 3-D steady-state thermal-fluid coupled simulation models of twinroll, three-roll, and four-roll layouts were established. The results indicate that increasing casting roll number can improve the nominal cast-rolling velocity, service life of the casting roll, temperature uniformity, strain uniformity, and strain rate uniformity through regulating the heat transfer and mass transfer. Considering the manufacturing feasibility, the MRSLCRB equipment based on the three-roll layout was designed. Cu/steel cladding bars with uniform circumferential performance were fabricated, and the forming mechanism was revealed. The multi-field coupled analysis method provides a way to control heat and mass transfer uniformity, and the successful attempts of various typical metal cladding materials inspire exploring new forming processes.
Lui, Edward W.Medvedev, Alexander E.Edwards, DarrenLeary, Martin...
9页
查看更多>>摘要：Titanium alloys such as Ti-6Al-4V offer a potential lightweight alternative to traditional armour steels for ballistic protection due to their reduced density of approximately 60 % that of steel and tensile properties better than rolled homogenous armour steel. The manufacture of metallic armour often requires substantial thermomechanical processing to meet necessary ballistic performance specifications and thus restricts the complexity of armour designs. Additive manufacturing of Ti-6Al-4V has matured significantly in recent years, achieving outstanding mechanical properties in the as-built condition. In this study, Ti-6Al-4V plates were additively manufactured using both laser powder bed fusion and direct laser metal deposition for ballistic testing. The plates were built in different orientations and subjected to pre-heating or post heat-treatment to investigate the microstructural effect on the ballistic velocity limit (V50). The results show that plates with lamellar microstructure formed through martensite decomposition had higher V50 compared to lamellar microstructure formed via slow cooling through the beta-transus. The post heat-treatment increased the V50 due to coarsening of the alpha-lath and stress relief. It is also apparent that anisotropy of the microstructure, specifically the columnar prior-beta grains, affects the ballistic performance. A higher V50 was achieved when the columnar grains were aligned perpendicular to the projectile impact direction.
查看更多>>摘要：This paper develops an analytical model of temperature in Laser Powder Bed Fusion (LPBF) considering the geometrical effect of the build part, which is reflected by the part size and shape. The model is established based on the moving point heat source under a semi-infinite medium. A modified coefficient is utilized to calibrate the temperature along the build direction. The heat sink is adopted to consider the heat loss at the edge of the build part, and the superposition method is applied to calculate the multi-tracks effect of the laser beam. The material thermal properties are dependent on the temperature, and an iteration method is utilized to obtain the dynamic stable melt pool during the process. To validate the proposed model, the experimental data in the published paper are compared with the model predictions. Good agreement is found about the melt pool size. Based on the verified model, a sensitivity analysis of temperature with respect to the laser process parameters, the material properties, and the geometry of the build part is discussed. Both the depth and width of the melt pool have a negative relationship with the size of the part within the explored range. It is also shown that the size of the melt pool has a negative correlation with the length of the previous track, which is determined by the shape of the build part.
查看更多>>摘要：The use of multi-materials structures is nowadays one of the most sought solutions to decrease weight and reduce both emission of greenhouse gases and fuel consumption in the automotive industry. Dissimilar joining of aluminum (Al) alloys to steels by fusion-based welding technologies is often difficult to achieve as a result of the significant mismatch in these materials' physical and chemical properties. Moreover, when mixed in the liquid state, hard and brittle intermetallic compounds are easily formed. Due to characteristics that include high processing speed, flexibility and energy density, multiple attempts have been made to join Al to steel using laser based processes. This thorough review article provides a comprehensive and exhausting analysis of the recent achievements and progress on joining of Al alloys to steel by various laser-based joining processes, including laser keyhole welding, laser welding-brazing, laser-arc welding, laser-assisted friction stir welding, laser roll pressure welding and joining based on laser additive manufacturing. This paper also evaluates the joining conditions, filler materials, phase constitution, microstructure, mechanical properties and joining mechanisms associated to each process. Furthermore, special emphasis is given to factors affecting the joint strength such as welding defects, joint geometry, intermetallic compounds formation and interfacial strength. The review is then concluded with an outlook providing the summary and future trends of this field.
查看更多>>摘要：Tungsten carbide reinforced iron-based metal-matrix (WC-Fe) composite coatings, for the first time, have been fabricated on carbon steel substrate by the laser wire cladding with a novel type of Fe-based tubular cored wire. The processing characteristics have been systematically investigated by cladding of single tracks at varying operating parameters. In order to guide the actual production and predict the influence of different parameters on the typical processing characteristics in terms of wire stubbing transfer, wire plunging transfer, and liquid spreading transfer mode, a process window has been established. The experimental results show that the unmelted defects can be found in the coatings produced in the stubbing transfer mode, while most of the coatings obtained in the liquid spreading transfer mode have a high dilution degree ( 13 %) and a low content of retained particles (<15 %). Only the coatings fabricated in the wire plunging transfer mode possess a low dilution ratio (<13 %) and a high volume fraction of retained particles (15-26 %). The microstructural evolution in these coatings have been investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD). The ex-situ tungsten carbide particles are partially dissolved and interact with the matrix in the molten pool, resulting in the M6C (Fe3W3C) reaction layer around the retained particles. The faceted M6C carbides and the herringbone eutectic M6C carbides are found to be the primary precipitations in the coatings, combined with the presence of retained particles, the wear resistance of the WC-Fe coatings is significantly improved.
Chabok, AliCao, Huatangvan der Aa, EllenPei, Yutao...
16页
查看更多>>摘要：While the automotive industry is striving for the reduction of car body weight to increase the fuel efficiency and to reduce CO2 emission without compromising the safety and crashworthiness of vehicles, a new generation of advanced high strength steels (AHSS) have emerged as excellent candidates to meet these requirements. However, their integration into the car body structure is associated with welding-related problems. This research utilizes a novel approach to establish a fundamental correlation between welding parameters, microstructure and mechanical performance of AHSS resistance spot welds. In-situ micro-cantilever bending experiments are executed and analyzed in a quantitative manner to evaluate the effect of texture and post-welding heat treatment on the local fracture toughness of spot welds. A striking finding is that, through a switch from single to double pulse weld scheme, the texture of martensite formed in the fusion zone becomes responsible for a significantly higher fracture toughness of the area in front of the pre-crack. In addition, it is found that paint baking heat treatment also results in a much enhanced fracture toughness through tempering of the martensitic microstructure. A quantitative correlation is made between the micro-scale fracture toughness and macro-scale mechanical performance of advanced high strength steel welds.
查看更多>>摘要：Aiming at the preparation and forming of SS/CFRTP/SS composite components (CFRTP, thermoplastic carbon fiber composites; SS, stainless-steel), a mixed co-punching forming method of carbon fiber composites and stainless-steel is proposed. The effects of different surface treatments of stainless-steel on the shear strength, bending strength and crushing energy absorption of SS/CFRTP/SS composite components were also investigated, and the effects of ply angle on crushing energy absorption and bending strength of composites components were studied. The results show that the effect of SS/CFRTP/SS composite components prepared by mixed co-punching is very ideal. The bending strength of SS/CFRTP/SS composite component with 0 degrees/45 degrees/90 degrees ply is the best, and the 0-direction ply has the best energy absorption effect. The addition of PA6 material between layers did not enhance the effect. The mechanical properties of SS/CFRTP/SS composite components with coupling agent after wire brush grinding are better than those obtained by only wire brush grinding. XPS analysis shows that the added silane coupling agent becomes a bridge to transfer stress load between the two materials through chemical reaction with the surfaces of the two materials. The micropores formed after surface treatment of stainless-steel form interlocking connection with CFRTP matrix. The excellent composite effect of SS/CFRTP/SS composite components is the result of physical and chemical interaction.
查看更多>>摘要：Metal matrix composites (MMCs), combining the unique advantages of two or more constituents, have been recognized as a promising structural material system. Particularly, MMCs reinforced by carbon fibers (CFs) have opened new material design routes towards increased strength-to-weight ratios. Here, we demonstrate a low-cost one-step deposition of CF reinforced stainless steel (CFRSS) composites by twin-wire arc spray on low-alloy steel (LAS) substrates. The CFs are self-assembled and grow coherently, up to 100 s of mu m in length, along the splatdomain boundaries with enhanced bonding to their vicinals through partial oxidation. Structural and electrochemical studies reveal a pitting corrosion of the CFRSS layer in aqueous NaCl (3.5 wt.%) electrolyte and the corrosion passivation is apparently larger than that of the LAS substrate. Both the micro-and nano-hardness of the CFRSS layer are improved to over 4 times higher than that of the LAS substrate. These property enhancements indicate that this low-cost one-step process could revolutionize protective coatings on LAS against corrosion and/or erosion under aggressive conditions.
NSTL
Elsevier