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With the increasing requirements of automotive lightweighting, metal/CFRP laminates are increasingly used. In this paper, Al/CFRP laminates were prepared using an integrated hot press curing method, and the optimum curing conditions were determined using the single-lap shear test at 130 °C for 45 min. The effects of fiber lay-up, forming speed, and metal layer thickness on bending springback were investigated using the V-shaped bending test and Abaqus finite element analysis method. The results show that fiber lay-up has an important influence on springback. Among the five different fiber lay-ups (0° unidirectional, 90° unidirectional, 0° orthotropic, 90° orthotropic, and 45° orthotropic), the 45° orthotropic lay-up had the lowest springback rate of 1.11%. Increasing the thickness of the sheet metal can significantly reduce the resilience rate. As the sheet thickness increased from 2 mm to 3 mm, the springback of the 90° unidirectional lay-up decreased by 43%. Springback was not sensitive to forming speed, and the difference in springback was within 1% at different forming speeds. The damage behavior of the forming process was analyzed using the three-dimensional Hashin damage law with the Vumat subroutine and microscopic analysis. Fiber and resin damage under 45° orthotropic lay-up conditions was relatively small compared to fiber damage under 0° unidirectional lay-up and resin damage under 90° unidirectional lay-up. [ABSTRACT FROM AUTHOR]

Highlights: [•] We proposed two constitutive equations with varying parameters. [•] The phenomenological equation has high accuracy in a local range. [•] The empirical equation has higher accuracy in a wide range. [•] The two equations have a good ability to model superplastic flow behavior. [Copyright &y& Elsevier]

Highlights This article proposes a 6061‐T6 Al alloy and carbon fiber hybrid composite material pre‐curing and forming integrated new process, which can significantly reduce the hybrid composite material processing time, improve the production efficiency, and provide the possibility of hybrid composite materials in automotive parts applications. The process started by placing hand‐stacked carbon fiber reinforced plastic (CFRP) composites on the surface of 6061 Al alloy sheets, followed by bonding and pre‐curing of the CFRP to the Al alloy sheets through two different sets of dies in a hydraulic press, and ultimately full curing in an aging furnace. Mechanical properties of the CFRP/Al hybrid composite material were measured by flexural tests. The results show that the flexural strength of CFRP/Al hybrid composites with different layups ([90]12, [0/45/90/−45]3, and [0]12) was increased by 159%, 93.4%, and 67.9%, respectively, compared with the single 6061 Al alloy. According to the macro‐morphological observation, [90]12 lay‐up parts have the least thinning. According to the microstructure observation, no obvious cracks or voids were found in the [90]12 lay‐up parts. Elongated cracks and void defects could be found in the [0]12 lay‐up parts. For the [0/45/90/−45]3 lay‐up parts, voids are mainly exist in ±45°layups. The results of the spring‐back analysis show that the standard deviation of the formed parts obtained from the three lay‐up methods is within 1 mm, indicating that the forming effect is good. New process improves productivity and reduces production costs The flexural strength of CFRP/Al hybrid parts is greatly improved [90]°12 lay‐up parts have the least thinning and no cracks were found The forming precision of the three lay‐up parts is good [ABSTRACT FROM AUTHOR]

To solve the problem of poor formability of 7075-T6 aluminum alloy at room temperature and the degradation of properties after conventional warm forming, this paper put forward the contact heating warm forming (CHWF) process, which can make aluminum alloy blank reach the forming temperature in a very short time through the heated plates with pressure. Firstly, the uniaxial warm tensile tests with contact heating were carried out at 160–240 °C. Then the parameters of CHWF, namely forming temperature, contact pressure and holding time, were optimized based on the response surface and genetic algorithm. The U-shaped parts were obtained by using the optimal parameters. The results showed that the work hardening and dynamic recovery softening of 7075-T6 aluminum alloy at 200 °C could reach an equilibrium state, and the uniform plastic deformation ability was strong. The optimal parameters of CHWF were the forming temperature of 200 °C, the contact pressure of 10 MPa, and the holding time of 16 s. The U-shaped parts obtained by the optimal process had a small springback angle. Compared with the warm forming by using heating furnace, η′ precipitate did not grow significantly under CHWF condition and the hardness could reach 93% of T6 state. [ABSTRACT FROM AUTHOR]

7075 aluminum alloy is becoming an ideal material for the manufacture of vehicle body parts due to the demands for energy-saving and lighter vehicles. To solve the problem that the strength of 7075-T6 aluminum alloy decreases due to over-aging after warm forming, contact heating warm forming (CHWF) technology was proposed in this work. Contact heating is a fast and efficient heating method that can make the blank reach the target temperature in a very short time. In this work, the effect of contact heating on the mechanical properties and microstructures of 7075-T6 aluminum alloy after warm forming and paint-baking (PB) was studied. It only took about 11.5 s to heat the 2 mm 7075 aluminum alloy sheet to 200 ℃ by contact heating, and the strength and the hardness of the formed parts could reach 94% and 92.5% of T6 condition, respectively. In contrast, the heating furnace needed 690 s to heat the sheet to 200 °C, and the strength and the hardness of the formed parts were 87% and 85.4% of T6 condition, respectively. Due to the fast heating rate of contact heating (17.5 ℃/s), the atoms and vacancies in the matrix did not have time to undergo diffusion and aggregation, so that the precipitates could not coarsen obviously. As a result, most of the η' precipitates in the T6 condition were retained. However, long-term heating in the furnace led to the transformation of η' precipitates into coarse η phase and the loss of strength and hardness. [ABSTRACT FROM AUTHOR]

• The interface layer of modified epoxy resin was prepared by means of liquid phase physical deposition combined with hot-press process. • The interfacial shear force and fracture energy of modified resin sample are 746.60 N and 1718.14 J/m2, which are 29 % and 75 % higher than raw resin sample. • A new C-Si chemical bond is formed at the interface, which improves the strength of the interface. • The coordinated and smooth transition layer improves the toughness of the interface. In order to improve the interfacial strength and toughness of aluminum alloys and CFRP (carbon fiber reinforced plastics) hybrid laminates, modified resin with lower porosity was prepared by adding nano silica treated with silane coupling agent into epoxy resin. Al/CFRP hybrid laminates with modified resin were prepared by physical liquid deposition method and hot-press process. The strength and toughness of Al/CFRP hybrid laminates with modified resin were evaluated by tensile shear test and end notch fracture (ENF) test. The experimental results showed that the interfacial shear strength of Al/CFRP hybrid modified resin laminates is 18.8 ± 0.8 MPa and the fracture energy is 1546.33 ± 10.26 J /m2, which is 28.76 % and 15.38 % higher than that of Al/CFRP hybrid laminates with raw resin, respectively. The well-dispersed silicon nanoparticles effectively mitigate internal stress during the cross-linking process of the modified resin, thereby diminishing the dimensions of microcracks within the modified resin. The transition layer of the modified resin interface formed a cooperative and smooth structure. This structure can ensure that the transition of elements in the interface layer is smooth, and it is not easy to cause stress concentration. The formation of new bonds (C-Si bonds) at the interface of the modified resin indicates an enhancement of bonding strength at the interface, superimposing upon van der Waals forces, thereby enhancing the adhesive strength of the modified resin interface. [ABSTRACT FROM AUTHOR]

The biomimetic interface of Al/CFRP hybrid composite material was obtained by combining laser surface treatment and hot-pressing process. The experimental results showed that the tensile shear strength and fracture energy of the biomimetic interface were 44.5 MPa and 1652 J/m2, which were 224% and 72.6% higher than those of the untreated interface. The new C-O-Al chemical bond was formed at the biomimetic interface, which replaced the van der Waals force and improved the interface strength. The transition layer of the biomimetic interface can effectively delay the transmission of cracks at the interface. The finite element results showed that the stress distribution of biomimetic interface was uniform and stress concentration was not obvious. The strengthening and toughening effect of the interface is mainly due to the pinning effect of mechanical interlocking of the interface and the behavior of crack deflection of the transition layer. • A bionic interface of Al/CFRP hybrid composite was manufactured through hot press forming and laser surface treatment. • Beetle elytra-inspired barb connection structure endow the interface with superior strength and fracture toughness. • The new C-O-Al chemical bond at the bionic interface improves the strength of the interface. • The transition layer of bionic interface can greatly buffer the impact force of the interface. [ABSTRACT FROM AUTHOR]

Composite materials are more and more widely used in the automotive industry with the increasing requirements of lightweight design. In order to obtain automotive parts with excellent comprehensive mechanical properties, the 7075-T6 aluminum alloy was integrated with Carbon Fiber Reinforced Plastic (CFRP) by using thermoforming process. The influence of four forming methods on the forming process, forming accuracy, and interface bonding strength was studied in this work. A finite element model based on cohesion and forming was established to study the integrated thermoforming and properties prediction of Al/CFRP hybrid composites. The results showed that forming CFRP and unformed 7075 Al aluminum alloy sheet together required higher forming energy and the formed parts had higher Mises stresses. When the CFRP was located below 7075 aluminum alloy sheet, the uneven stress distribution due to the severe deformation of the resin resulted in the worst forming accuracy. For all four processes, the thickness of the formed parts decreased at the round corners and side wall area, increased at the flange area, and changed little at bottom surface. The thickness distribution of the formed part depends on the deformation process and the contact pressure between the tools and the blank. Greater contact pressure resulted in greater thinning rate. For the processes of preformed 7075 aluminum alloy, although less forming force was needed, the interface debonding risk between 7075 aluminum alloy and CFRP might arise due to the small contact pressure. [ABSTRACT FROM AUTHOR]

During air bending of sheet metals, the correction of punch stroke for springback control is always implemented through repeated trial bending until achieving the forming accuracy of bending parts. In this study, a modelling method for correction of punch stroke is presented for guiding trial bending based on a data-driven technique. Firstly, the big data for the model are mainly generated from a large number of finite element simulations, considering many variables, e.g., material parameters, dimensions of V-dies and blanks, and processing parameters. Based on the big data, two punch stroke correction models are developed via neural network and dimensional analysis, respectively. The analytic comparison shows that the neural network model is more suitable for guiding trial bending of sheet metals than the dimensional analysis model, which has mechanical significance. The actual trial bending tests prove that the neural-network-based punch stroke correction model presents great versatility and accuracy in the guidance of trial bending, leading to a reduction in the number of trial bends and an improvement in the production efficiency of air bending. [ABSTRACT FROM AUTHOR]