Clad Rolling Research Articles

Optimization of weldability and joint strength of Al-Mg-Si with additional Al-Si cladding based on a design of experiments investigation

Some aluminum alloys, such as those alloyed with Si and Mg, are difficult to weld due to their susceptibility to hot cracking. Previous research has investigated this challenge in resistance spot welding (RSW). To improve the weldability of the AW-6111 aluminum alloy, the roll cladding process was employed, combining it with AW-4045 as the cladding material. This resulted in a wider weld lobe, improved electrode wear, and enhanced joint quality. However, it is evident that the cladded material could benefit from improved welding conditions. Despite a larger nugget diameter, similar mechanical properties were observed for both the minimum and maximum boundary conditions of the weld lobe, determined by Inom and Imax.This study employed a design of experiments approach to optimize the joint strength and improve the weld quality of the AW-6111 + AW-4045 cladded sheets. The tensile-shear test results demonstrated an improvement in lap-shear strength of 38 % and 44 % compared with the previous study. Furthermore, the test samples predominantly exhibited a ductile partial thickness failure mode, and a significant improvement in the weld nugget quality of the cladded AW-6111 + AW-4045 was observed. The cladded joints also exhibited a Si alloying content of approximately 5 % in the heat-affected zone and fusion zone, thereby reducing the risk of crack formation and propagation, thus improving significantly the weld quality. The results of this study contribute with the continuous validation of Al alloys for the transport industry and with the use of cladding technology to enhance the aluminum sheet properties and respective weld quality.

Modeling and analysis of deformation characteristics for the two-layered metal clad plate produced by asymmetric rolling

Accurate prediction of deformation behavior of metal plate in deformation zone is the key point for rolling cladding process. At present, there is a lack of accurate analytical model about the deformation of metal plate in deformation zone. Therefore, an analytical model of the deformation characteristics in deformation zone for the two-layered metal clad plate produced by asymmetric rolling is established according to the practical requirements. Firstly, the stream function field model of the clad plate in the deformation zone is founded by using the stream function method. Based on the stream function field, the velocity field model of the clad plate in the deformation zone is established, and the precision of the velocity field model is demonstrated by the comparison between the finite element and the model analytical results. Based on upper bound theory, the layer thickness of the clad plate after rolling and the ratio of deformation power, friction power and shear power to the total power were calculated by minimizing the total rolling power. Finally, based on the thickness of clad plate after rolling and velocity field model, an analytical model is established to calculate the equivalent strain of the clad plate in the deformation zone. The accuracy of the analytical model is tested by the rolling cladding experiments and the finite element simulations. The results indicate that the analytical model has high precision and which makes it useful to predict the deformation behavior in the clad plate rolling process.

Effect of annealing process on the interfacial microstructure evolution and mechanical properties of 7050 aluminum alloy clad plates

• Aluminum alloy thick plates are produced by vacuum roll cladding technology. • The mechanical properties of the interface are improved by annealing treatment. • The Mg and O elements diffuse at the interface during the annealing process. • The Al 2 O 3 at the interface mainly evolves to MgO. In this research, aluminum alloy thick plates are produced by vacuum roll cladding (VRC) technology. And the annealing experiments with different annealing temperature and holding time are carried out for the clad plates. The results show that the tensile strength and elongation of the bonding interface are positively correlated with the annealing temperature and holding time. The fracture mode of the bond interface gradually changes from brittle fracture to ductile fracture. The Mg and O elements diffuse at the interface during the annealing process, and the Al 2 O 3 gradually evolves into MgO (mainly) and MgAl 2 O 4 . After holding at 470 ℃ for 24 h, the tensile strength of the interface is 427 MPa, which fully reaches the level of the matrix. Therefore, the dissolution and evolution of interfacial oxide contribute to the recovery of mechanical properties at the bonding interface.

Interface microstructure and bonding mechanisms of 7050 aluminum alloy thick plates produced by vacuum roll cladding

Vacuum roll cladding (VRC) based on friction stir welding (FSW) is applied to prepare aluminum alloy thick plates, and the effect of rolling reduction ratios (60%, 70%, 80%) on the microstructure and mechanical properties at the bonding interface of aluminum alloy clad plates are investigated. The results show that voids at the interface are gradually closed and the original interface finally disappears with the increase of rolling reduction ratios. There are 3 kinds of recrystallization mechanisms at the interface during hot rolling. The contributions to the healing of the interface are in the following order: geometric dynamic recrystallization (GDRX) > discontinuous dynamic recrystallization (DDRX) > continuous dynamic recrystallization (CDRX). At a rolling reduction ratio of 80%, GDRX characterized by the “pinch-off” of original grains mainly occurs at the interface, and no aggregation of defects and impurity elements is detected. The tensile shear strength and fracture displacement at the interface both reach the level of the matrix, which indicates that a good metallurgical bonding has been achieved at the interface. Therefore, the key to improving the interfacial healing quality is to break the interfacial oxide film and further induce recrystallization at the interface through a large rolling reduction ratio.

Fe/Mg/Fe Multilayer Composite Sheet Fabricated by Roll Cladding.

A new multilayer composite sheet consisting of Fe/Mg/Fe was fabricated from galvanized steels and Mg alloy sheets via roll cladding. The clad steel improved the Mg surface hardness from HV 65 to HV 132. Bonding occurred as the reduction ratios increased up to over 10%. Investigation of the microstructure of the Mg/steel interface revealed a 5 μm- to 10 μm-thick transition layer between Mg and each steel sheet, consisting of Zn and an intermetallic compound (0.97Mg–0.03Zn). Zinc coating from the galvanized steel sheet improved the metallurgical bonding between Mg and Fe by forming new intermetallic phases.

Enhancement on the Tribological Properties of the Multilayer RGO/Al Matrix Composites by Cu-Coating Method.

Multilayer reduced graphene oxide (mrGO) was chemically modified by electroless plating of copper on surface to form mrGO-Cu. The scanning electron microscope (SEM) and transmission electron microscope (TEM) analysis revealed that nano-Cu particles were uniformly dispersed on the surface of mrGO. The mrGO-Cu powders were further utilized as reinforcements for aluminum (Al) matrix and the mrGO-Cu/Al composite was successfully fabricated through clad rolling of milled powder. The tribological properties of the mrGO-Cu/Al composites were explored. The tribological results show that the mrGO-Cu could reduce the friction coefficient and wear loss of mrGO-Cu/Al composites, since the mrGO-Cu participated in lubricating processes due to the formation of a transfer layer on the contact surface. Furthermore, it is found that the composition of mrGO-Cu could significantly influence the tribological properties of the mrGO-Cu/Al composites. The composites with 4% of mrGO-Cu for composites exhibited the best tribological behavior, which transformed from adhesive wear to abrasive wear, due to the formation of a graphite lubricating film.

Cold clad rolling of Al-Ni nanopowders between the layers of aluminium foil to produce high-strength high-density reactive materials

Cold clad rolling of Al-Ni nanopowders between the layers of aluminium foil to produce high-strength high-density reactive materials

Manufacturing Process and Interface Properties of Vacuum Rolling Large-Area Titanium-Steel Cladding Plate

In order to obtain large-area titanium-steel cladding plate by vacuum rolling, the manufacturing process was discussed with the Hypermesh/LS-DYNA simulation software. The result showed that the reduction rates of each rolling pass were 20, 25 and 33%, respectively. And the total rate was 60%. Moreover, the vacuum rolling process mainly included the following steps: welding preparation, drilling vacuum holes, composite and assembly, vacuum extraction, accumulative seal welding, preheating and rolling. The final size of the cladding plate was 1650 × 12000 × (4 + 40) mm. It could be found that the vacuum rolling interface of the titanium-steel cladding plate was mainly divided into four parts: steel layer (I), decarburized layer (II), bonding layer (III) and titanium layer (IV). Acicular widmanstatten structure of β-titanium was formed in zone IV, which might reduce the impact toughness of joint. The microhardness test results showed that the hardness near the interface was relatively high. Macroscopically, the average shear strength (297 MPa) and the average tensile strength (590 MPa) were both much higher than the standard. However, the brittle fracture mode of shear specimens might decrease the joint property of vacuum rolling cladding plate.

The Determining Role of Nb Interlayer on Interfacial Microstructure and Mechanical Properties of Ti/Steel Clad Plate by Vacuum Rolling Cladding.

We elucidate here the determining role of Nb interlayer on mechanical properties of Ti/steel clad plate fabricated by vacuum rolling cladding (VRC) as a function of different heating temperatures. A critical analysis on the clad interface via electron probe micro-analyzer, X-ray diffractometer and shear testing were conducted to investigate the influence of TiC, Fe-Nb and TiFe compounds and Nb-Ti solid solution on microstructural evolution and shear properties of Ti/steel clad plate. The inter-diffusion between Ti, C and Fe was effectively restrained by adding the Nb interlayer at heating temperature of 800 °C, and average shear strength of 279 MPa was achieved. With increase of heating temperature, Nb-Ti solid solution was formed at the Ti/Nb interface, which reduced mechanical properties of clad plate at 900 °C. At 1000 °C, TiC and Nb-Fe compounds and Nb-Ti solid solution were formed at the interface, and minimum average shear strength of 152 MPa was achieved. The detailed analysis on the clad interface suggested that ideal shear strength can be obtained through the addition of Nb interlayer and selecting appropriate heating temperature.

Effect of interfacial compounds on mechanical properties of titanium–steel vacuum roll-cladding plates

ABSTRACTThe titanium–steel clad plates were prepared by vacuum roll cladding. Ti–Fe compounds and TiC were observed at different cooling rates after rolling. Optical microscopy, electron microprobe analyser, X-ray diffraction and shear test studies were carried out to study the effect of Ti–Fe compounds and TiC on the ultimate microstructure and mechanical properties of titanium–steel clad plates. At a cooling rate of 6.2°C/min, TiC and Ti–Fe compounds seriously impacted the mechanical properties of the clad plate. At a cooling rate of 1.8°C/min, the thickness of the TiC layer was optimal much that the maximum shear strength of 296 MPa was obtained. At a cooling rate of 0.6°C/min, the thickness of the TiC layer was relatively thick, which affected the mechanical properties of clad plates.

Solder Interconnection of Aluminum Foil Rear Side Metallization for Passivated Emitter and Rear Solar Cells

Foil metallized (FolMet) solar cells combine the high-efficiency PERC technology and a cost-efficient rear side metallization based on a 9 µm thin aluminum foil. Laser fired contacts are used to attach the foil to the rear side and allow for the mechanical and electrical contact to the cell. Direct soldering on aluminum is hampered by a native oxide film formed immediately when exposed to air. To realize the cell interconnection by a standard solder process the Al foil is coated by sputter deposition or roll cladding of solderable layers. This work evaluates the solderability of 200 µm thick coated Al foils with the common solder interconnection process established in photovoltaics using standard copper ribbons for module integration. Our analysis reveals for both coating approaches strong initial mechanical adhesion of > 4 N/mm after soldering and very low contact resistivities of < 1.6 µ∙cm2. The contact resistivity shows no degradation after isothermal aging within 1000 hours at 85 °C. The mechanical adhesion of the sputter coated Al foils remains at 3 N/mm under thermal aging of more than 1000 h at 85 °C whereas the adhesion for the Al foils coated by roll cladding drops strongly to values of < 1 N/mm already after 50 hours. SEM images indicate that this effect is caused by re-oxidation of the aluminum surface supported by micro cracks in the solderable top layer.

Effect of vacuum level on microstructure and mechanical properties of titanium–steel vacuum roll clad plates

Vacuum roll cladding (VRC) was used to bond pure titanium (Ti) plate to a plain low carbon steel (Q345) with the aim of obtaining a high-quality Ti–steel clad plate. The effect of interfacial compound on the microstructure and mechanical properties of Ti–steel clad plate was studied by electron probe microanalysis, scanning electron microscopy, X-ray diffraction and shear test. The clad plates were heated at 850 °C for 120 min and welded at different levels of vacuum. The results indicated that the cracked zone of the bonded interface decreased significantly with the increase in the level of vacuum during welding. Welding at atmospheric pressure, the randomly distributed TiN damaged the continuity of TiC and the uniformly diffused region of Ti and Fe at the bonded interface, while welding in vacuum of 1 × 10−2 Pa, maximum shear strength of 298 MPa was obtained because of the decrease in TiN content.

Effect of Annealing on Properties of AgCuNiCe/TU1 Rolling Clad Sheet

AgCuNiCe/TU1 (TU1 refers to oxygen free copper) electrical contact composite is a new type and key material with durable and reliable switching operations of contacts used for converter and brush in the direct current micro-motor. AgCuNiCe/TU1 layered composite sheets were fabricated by cold roll cladding process and then diffusion annealed at different temperatures. The influences of annealing on microstructure, bonding property and electrical conductivity of the composite were investigated. The research results indicate that the interfacial bonding performance and electrical conductivity depended strongly on the annealing temperature. The ideal annealing temperature was found to be 600 °C.

Heat dissipative Pb-free bonding technology using Al-rich Zn/Al/Zn clad solder

Al-rich Zn/Al/Zn clad solder were developed as Pb-free solder for a die-attachment. The Zn/Al/Zn clad solder was produced by clad rolling of Zn and Al strips in order to prevent Al from oxidation and improve wettability. The Zn/Al/Zn clad solder was melted at 382°C after solid-state interdiffusion of the Zn and Al layers. Bonding was successfully achieved with bonding pressure of a few kilopascals. Thermal cycle life of Invar-to-Cu substrate joint using the Zn/Al/Zn clad solder was longer than that of Pb-Sn-Ag solder. No Kirkendall voids were observed in the vicinity of the bonded interface after ageing at 250 °C for 1000 h.

Experimental Investigations on the Influence of the Thermal Conditions During Composite Casting on the Microstructure of Cu–Al Bilayer Compounds

Metallic material compounds are of technical interest as they allow the combining of specific properties of different materials into one component. In particular, compounds of copper (Cu) and aluminum (Al) are a current object of research. There are different fabrication processes, such as roll cladding or overlay welding. In recent years, a variety of alternative bonding methods were investigated, among other composite casting processes. A notable problem of Cu–Al composites is the formation of hard and brittle interface layers which reduce the mechanical properties of the compounds. Therefore, the reduction of these layers is one of the objectives of the development of new fabrication processes to realize suitable industrial applications. In this study, gravity casting experiments are carried out to produce Cu–Al bilayer composites and to determine the influence of the thermal process parameters on their properties. Two experimental setups using sand molds are developed, and casting experiments with varying thermal parameters are carried out. Specimens of the cast composites are extracted, metallographic examined and the hardness profile is determined. Hence, it is possible to identify the influence of thermal parameters on microstructure and hardness of cast Cu–Al bilayer composites.

Investigation of Cold Pressure Welding: Cohesion Coefficient of Copper

Joining materials by forming is an interesting approach to the manufacture of hybrid (multi material) parts. By establishing a cold pressure weld between metallic surfaces, high quality joints with superior properties can be achieved. Reliable cold welding conditions are difficult to set up, however, since the weld initiation requires extraordinary clean, virtually sheer surfaces. Until today such conditions could only be achieved under a high vacuum conditions. Various studies on cold pressure welding reported that under vacuum welds can be established at significantly lower deformation than in a normal atmosphere. Since adverse deformation is currently needed in industrial cold pressure welding processes like the cold roll cladding of metal bands, a new process with in-line electrochemical surface treatment, is investigated. The ECUF process is intended to supply clean and thereby highly activated surfaces to the cold pressure welding process.This paper presents first results on the weld-ability of copper specimens with regard to the influence of the welding environment: air, argon and KCl solution. Butt welds were made by pressure welding of previously fractured specimens.

Microstructures and Properties of Graphene‐Cu/Al Composite Prepared by a Novel Process Through Clad Forming and Improving Wettability with Copper

An improved Hummers method was adopted to prepare graphene oxide, which was then plated was plated with copper using a chemical approach to produce graphene‐Cu as an enhancement phase. Multilayer graphene was prepared, and its morphology exhibited a thin‐slice like structure. A graphene‐Cu‐reinforced pure aluminum composite with 3 wt% graphene‐Cu content was prepared by clad rolling. Most of the graphene‐Cu and CuO were distributed homogeneously in the composite. The tensile strength and hardness of the graphene‐Cu/Al composite were improved by 77.5 and 29.1%, respectively, compared with those of the aluminum matrix. The graphene‐Cu contributes to strength enhancement mainly through the synergistic action of two mechanisms: stress transfer and dispersion strengthening. The preliminary results achieved in this work demonstrate that graphene can act as an effective reinforcement in an aluminum matrix.

Reliable Copper and Aluminum Connections for High Power Applications in Electromobility

Investigations concerning the growth of intermetallic phases during the heat input both at the diffusion annealing of copper aluminum roll claddings and the subsequent welding process of copper-aluminum connections by using roll cladded inserts are compared to the analytical determination of phase growth. The temperature distribution in the cladding interface has been determined by thermal simulation, in order to calculate the growth of the intermetallic phases. A comparison between the width of the phases in the analytical calculation and the experiment is achieved. In consideration of high welding speeds, the energy input during the welding process is appraised in order to grade the growth of intermetallic phases. Furthermore the prevention of damage in the roll cladding interface by means of unadapted material thicknesses or welding parameters can be assessed analytically and numerically. The numerical simulations can determine the critical thickness of the roll cladding to avoid damage like exceeding growth of intermetallic phases.

Investigation of Deformation Behavior during Cold Rolling Cladding Process of Four-Layer Composite Aluminum Alloys

Two different types of aluminum alloys of AA5005 and AA6061 were used to fabricate four-layer laminated composite materials by the cold rolling cladding technology. The original sheet metals were annealed at 500 °C for three hours to achieve equiaxed microstructures, with an average grain size of 50 µm for AA5005 and 38 µm for AA6061. Tensile tests of these two alloys have been conducted and the results were used as the input parameters to build the finite element model. The influences of sample assembling order and frictional conditions on the deformation behavior have been studied in the present work. In the experiments, very good bonding with no delamination between four layers was attained. Similar hardness has been observed for both AA5005 layer (about 79.6 Hv) and AA6061 layer (about 80.3 Hv) in the laminated composite materials.

Evolution of deformation texture in Al/Al–Mg/Al composite sheets during cold-roll cladding

Al/Al–Mg/Al composite sheets were fabricated by roll cladding to investigate the evolution of deformation texture through the thickness direction. Electron backscatter diffraction (EBSD) was used to analyze the heterogeneity of deformation texture in each component layer of the composite sheets. Finite element analysis (FEA) was conducted to simulate the deformation history in each component layer during roll cladding. The deformation history from the FEA was used in a full-constraints polycrystal model to simulate the evolution of deformation texture through the thickness direction during roll cladding. The simulation results revealed that the development of distinct shear–strain texture components in the clad layer could be explained by the friction-induced shear component of a velocity gradient tensor.