Effect of friction,annealing conditions and hardness on the bond strength of Al/Al strips produced by cold roll bonding process

Layered materials have become an increasingly interesting topic in industrial development. Cold roll bonding (CRB) process, as a solid phase method of bonding same or different metals by rolling at room temperature, has been widely used in manufacturing process. In this paper, characteristics such as bond strength and threshold deformation of as-received commercial pure aluminum (AA1100) strips prepared by the cold roll bonding process are investigated. Bond strength is evaluated by the peeling test. The main factors evaluated included effects of different annealing time, annealing temperature, hardness, and the effect of friction coefficient on bond strength. It is found that bond strength is enhanced by increasing annealing time, friction coefficient, and annealing temperature but that it is inversely proportional to hardness.     

Bond strength evaluation of roll bonded bi-layer copper alloy strips in different rolling conditions

Roll bonding is a solid-state welding process to join similar and dissimilar metals and alloys and is widely used as a manufacturing process. In this study, bi-layer copper alloy strips were roll bonded at warm and cold conditions; and then the effects of parameters that create successful bonds, such as the amount of deformation by rolling and rolling temperature on the bond strength were investigated. For this purpose, faying surfaces were degreased and scratch brushed, being fractured coherently after entering roll gap at different reductions. As deformation proceeded and the roll pressure increased, these cracks quickly expanded into fissures. This process allowed the bond to be established between the underlying materials of the base metal layers, termed virgin metal, which were extruded through the cracks and fissures at the scratch brushed regions. The peel strengths of the bonds were measured and were found to increase when the rolling temperature or the thickness reduction are increased.     

Slab analysis of roll bonding of silver clad phosphor bronze sheets

Abstract

A numerical analysis program, based on slab analysis, was developed to calculate the stresses and strains that occur in the component layers of a composite sheet in the roll bite during the fabrication of clad metal (e.g. silver clad phosphor bronze) by roll bonding. Results calculated using the perfect plastic and strain hardening models were compared with experimental results: the results obtained using the strain hardening model were found to be in better agreement with values of rolling force and thickness of component layers measured after roll bonding. The program requires input data such as roll radius, initial thickness of the specimen, initial cladding thickness fraction, reduction ratio, coefficients of friction between rolls and material and between component layers, and front and back tensions. The coefficients of friction were evaluated indirectly by comparison of the measured rolling force with that calculated using slab analysis. Measured coefficients of friction varied with reduction ratio and initial thickness, but were independent of rolling speed.

MST/1334     

Progress in cold roll bonding of metals

Abstract

Layered composite materials have become an increasingly interesting topic in industrial development. Cold roll bonding (CRB), as a solid phase method of bonding same or different metals by rolling at room temperature, has been widely used in manufacturing large layered composite sheets and foils. In this paper, we provide a brief overview of a technology using layered composite materials produced by CRB and discuss the suitability of this technology in the fabrication of layered composite materials. The effects of process parameters on bonding, mainly including process and surface preparation conditions, have been analyzed. Bonding between two sheets can be realized when deformation reduction reaches a threshold value. However, it is essential to remove surface contamination layers to produce a satisfactory bond in CRB. It has been suggested that the degreasing and then scratch brushing of surfaces create a strong bonding between the layers. Bonding mechanisms, in which the film theory is expressed as the major mechanism in CRB, as well as bonding theoretical models, have also been reviewed. It has also been showed that it is easy for bcc structure metals to bond compared with fcc and hcp structure metals. In addition, hardness on bonding same metals plays an important part in CRB. Applications of composites produced by CRB in industrial fields are briefly reviewed and possible developments of CRB in the future are also described.     

Cold roll bonding of bimetallic sheets and strips

Abstract

The successful production of wide bimetallic sheets and strips by cold roll cladding depends on the technical solution of reduction of rolling load while still guaranteeing good bond quality. In the present paper, systematic experimental data on the cold roll cladding of aluminium–stainless steel, copper–stainless steel, and mild steel–stainless steel are correlated and the basic mechanism is discussed, aided by a scanning electron microscopy study of the separated interface. The effects of conventional rolling and cross-shear rolling (i.e. between rolls of differing peripheral speeds) on roll force and bonding strength are critically compared. It is found that use of the cross-shear cold rolling technique results in a significant reduction in rolling load for equal primary bonding strength and that the incorporation of an optimum final heat treatment considerably decreases the requirement on rolling.

MST/971     

Vacuum hot roll bonding of titanium alloy and stainless steel using nickel interlayer

Abstract

Vacuum hot roll bonding of titanium alloy and stainless steel using a nickel interlayer was investigated. No obvious reaction or diffusion layer occurs at the interface between stainless steel and nickel. The interface between titanium alloy and nickel consists of an occludent layer and diffusion layers, and there are the intermetallic compounds (TiNi₃, TiNi, Ti₂Ni and their mixtures) in the layers. The total thickness of intermetallic layers at the interface between titanium alloy and nickel increases with the bonding temperature, and the tensile strength of roll bonded joints decreases with the bonding temperature. The maximum tensile strength of 440·1 MPa was obtained at the bonding temperature of 760°C, the reduction of 20% and the rolling speed of 38 mm s^–1.     

Progress in cold roll bonding of metals

Layered composite materials have become an increasingly interesting topic in industrial development. Cold roll bonding (CRB), as a solid phase method of bonding same or different metals by rolling at room temperature, has been widely used in manufacturing large layered composite sheets and foils. In this paper, we provide a brief overview of a technology using layered composite materials produced by CRB and discuss the suitability of this technology in the fabrication of layered composite materials. The effects of process parameters on bonding, mainly including process and surface preparation conditions, have been analyzed. Bonding between two sheets can be realized when deformation reduction reaches a threshold value. However, it is essential to remove surface contamination layers to produce a satisfactory bond in CRB. It has been suggested that the degreasing and then scratch brushing of surfaces create a strong bonding between the layers. Bonding mechanisms, in which the film theory is expressed as the major mechanism in CRB, as well as bonding theoretical models, have also been reviewed. It has also been showed that it is easy for bcc structure metals to bond compared with fcc and hcp structure metals. In addition, hardness on bonding same metals plays an important part in CRB. Applications of composites produced by CRB in industrial fields are briefly reviewed and possible developments of CRB in the future are also described.     

Assessment of surface bonding strength in Al clad steel strip using electrical resistivity and peeling tests

Abstract

Aluminium clad steel strip successfully combines the surface properties of an aluminium alloy coating with the satisfactory mechanical properties of the steel substrate. The production of Al clad steel strip by rolling, however, is a more efficient and economical approach compared with other processes. In this investigation, trilayer strips of aluminium/steel/aluminium were produced using the cold roll bonding technique. The bonding strength between the layers and the electrical resistivity of the samples were measured using a peeling test and four point probe test, respectively. The effects of reduction of thickness, the friction condition between the outer layer and rolls, and the rolling velocity on the bonding strength and electrical resistivity of the samples were assessed. Finally, it is shown that the resistivity test can be used as a non-destructive test for the evaluation of the quality of bonding between the layers of aluminium clad steel strip.     

Bonding strength of Al/Mg/Al alloy tri-metallic laminates fabricated by hot rolling

One of major drawbacks of magnesium alloy is its low corrosion resistance, which can be improved by using an aluminized coating. In this paper, 7075 Al/Mg-12Gd-3Y-0·5Zr/7075 Al laminated composites were produced by a hot roll bonding method. The rolling temperature was determined based on the flow stresses of Mg-12Gd-3Y-0·5Zr magnesium alloy and 7075 Al alloy at elevated temperature. The bonding strength of the laminate composites and their mechanism were studied. The effects of the reduction ratio (single pass), the rolling temperature, and the subsequent annealing on the bonding strength were also investigated. It was observed that the bonding strength increased rapidly with the reduction ratio and slightly with the rolling temperature. The bonding strength increases with the annealing time until the annealing time reaches 2 h and then decreases. The mechanical bond plays a major role in the bonding strength.     

The effects of oxide film and annealing treatment on the bond strength of Al–Cu strips in cold roll bonding process

In this study the influence of Al₂O₃ coating and post-rolling annealing on the bond strength of dissimilar Al–Cu strips was investigated. For this purpose different degrees of thickness of Al₂O₃ film on Al strips were coated using anodizing process. Anodized aluminum and copper strips were then cold-rolled at different reduction levels. To investigate the effect of annealing treatment on bond strength after cold rolling, selected strips were annealed. Peeling test was used to investigate the effect of ceramic-based oxide film on bonding strength of Al–Cu strips. It was found that bond strength was improved after applying higher reductions and was decreased dramatically by providing oxide film. However, by increasing the thickness of oxide film up to a certain value (20 μm), bond strength was increased after which it was decreased. A decrease in bond strength was observed by post-rolling annealing.     

铜／铝冷轧复合板剥离性能及界面摩擦分析

采用同步轧制方法制备铜／铝复合板,研究了轧制变形量对于铜／铝复合板结合强度和剥离表面形貌的影响,分析了轧制复合界面摩擦机理。研究结果表明,复合板结合强度、剥离表面粘铝、铜基体表面裂纹数都随着轧制变形量的增大而增大。变形量为50％时,结合强度为2N／mm,变形量为60％时,结合强度为7N／mm,变形量为70％时,结合强度为14N／mm。轧制过程中,新鲜金属从结合面裂纹中挤压出来,受界面摩擦力剪切作用,两新鲜金属搓合在一起形成良好结合。     

Rolling strain effects on the interlaminar properties of roll bonded copper/aluminium metal laminates

Metal laminates of copper/aluminium were prepared by roll bonding at 430°C with various rolling strains. The effect of the rolling strain on the interface development and bond strength of the laminates was examined. It was found that as the rolling strain increased the bond strength of the laminates was generally enhanced in both as-rolled and sintered conditions. Critical post-rolling sintering conditions were found to exist for achieving optimum bond strengths of the laminates. It is evident that the development of optimum strength for the laminates is related to the formation of various intermetallic phases at the interface which is in turn determined by the diffusion activity of the metallic elements in the area. The greatest strength enhancement was generally observed to develop in the 60% rolled samples, suggesting that rolling strain of the roll bonding process may impose great influence on diffusion of the metallic elements. A higher copper content, without significant Kirkendall void formation, was found to build up in the interface area of the material, leading to development of strong interfacial phases. It is believed that a higher rolling strain of the roll bonding process has provided a greater area of physical contact between the bonded metals and imposed diffusion enhancement of the metallic elements across the interface.     

Investigation on the bond strength of Al-1100/St-12 roll bonded sheets,optimization and characterization

Al-1100/St-12 aluminum clad steel sheets were produced using roll bonding process at different reductions in thickness and with various supplemental annealing treatments. Experiments were conducted by applying the Taguchi method to obtain optimum condition for maximizing the joint strength. The joint strengths of the bi-layer sheets were evaluated by peel test. The Al/Fe intermetallic phases at the joint interface and the peeled surfaces were examined using scanning electron microscopy (SEM). Energy dispersive spectroscopy (EDS) and Vickers microhardness test were performed to characterize the intermetallic compounds. The results indicate that at the optimum condition of 0.50 reduction in thickness, 450 °C annealing temperature and 90 min annealing time, the bond strength reaches to the base aluminum sheet strength. In comparison to the reduction in thickness and annealing time, the annealing temperature has the most influence on the joint strength changes. In general, raising the annealing temperature up to 450 °C, increases the joint strength. However, annealing treatment at 500 °C reduces the strength due to the formation of brittle Al/Fe intermetallic layer at the bond interface. Additionally, increasing the reduction in thickness improves the joint strength.     

Microstructure and mechanical properties of Al/Al2O3 MMC produced by anodising and cold roll bonding

Abstract

In the present paper, Al–Al₂O₃ composite strips are produced by the cold roll bonding process of anodised aluminium strips. This technique has the flexibility to control the volume fraction of metal matrix composites by varying the oxide layer thickness on the anodised aluminium strip. Microhardness, tensile strength and elongation of composite strips are investigated as a function of quantity of alumina and the applied production method. It is found that higher quantities of alumina improve microhardness and tensile strength, while the elongation value decreases negligibly. Furthermore, prerolling annealing is found to be the best method of producing this composite via the cold roll bonding process. Finally, it is found that both monolithic aluminium and aluminium/alumina composite exhibited a ductile fracture, having dimples and shear zones.     

Influence of microwave annealing on direct bonded silicon wafers

Strong and nearly void free bonding was achieved using direct bonding followed by microwave annealing. Silicon wafers were cleaned, O₂ plasma surface activated, and bonded at room temperature. After microwave annealing at 400 °C, the bond strength of hydrophilic wafers was found to be in the range between 0.2 and 1.6 J/m². Additional heating of bonded wafers was done at elevated temperatures and for prolonged times using either rapid thermal annealing or microwave annealing. In either case, additional annealing showed no impact on wafer separation area, void, or bond strength. Thus, the initial microwave anneal dictated the ultimate bond strength regardless of subsequent annealing method. The mechanism for wafers bonded in this work involved dipole-dipole bonding and, hydrogen bonding. The initial microwave anneals typically required times less than 60 min. As a result, microwave annealing was shown to be a promising low temperature alternative for wafer bonding when compared to the currently used mechanical furnace anneals.     

Optimum rolling speed and relevant temperature- and reduction-dependent interfacial friction behavior during the break-down rolling of AZ31B alloy

The present study aimed to determine the optimum rolling speed for break-down rolling of as-cast AZ31B alloy and investigated the friction behavior associated with temperature- and reduction-sensitivity at the roll/plate contact interface. Tensile testing, formability evaluation and microstructural studies relevant to different rolling speeds were performed and finally the optimum operating rolling speed (50.0 ± 0.8 m/min) was obtained. Further, the effects of rolling reduction and initial temperature were assessed on the temperature variation, lateral spread and interfacial friction behavior at optimum rolling speed. The results showed that lower rolling speed (18.0 ± 0.8 m/min) resulted in an incompletely recrystallized structure where twins occupied relatively high volume fraction. Twinning dominated the deformation at rolling speed exceeding the optimum, resulting in the local recrystallization with shear bands and coarse grains. Rolling at 50.0 ± 0.8 m/min could get the best overall tensile properties and rolling formability due to the relatively high recrystallization degree and microstructure uniformity. An inverse method has been developed to determine the interfacial friction coefficient during interaction of AZ31B alloy with roll surfaces. When rolling at the optimum speed, the interfacial friction coefficient ranged from 0.16 to 0.58, which was strongly positively correlated with the reduction but slightly positively correlated with the initial temperature. Depended on the rolling characteristics, external friction effect coefficient ranged from 1.25 to 2.35 and it exhibited positive correlation with both the initial rolling temperature and rolling reduction.     

Effects of temperature and B4C content on the bonding properties of roll-bonded aluminum strips

The presence of ceramic particles between metal strips in metal matrix composite processing by roll bonding affects their bonding properties. In this study, roll bonding of commercial pure aluminum (AA1100) strips in the presence of various B₄C contents at different thickness reductions was focused. Furthermore, the effect of rolling temperature (at ambient temperature and 473 K) on the bonding properties of the strips was investigated via peeling tests. The results showed that the presence of the B₄C particles between the aluminum strips reduces the bond strength and weld efficiency; in contrast, they are increased by increasing temperature. Therefore, by increasing temperature it is possible to use the higher amounts of the B₄C particles between the aluminum strips.     

Multipass cold rolling and resultant mechanical properties of a Cr-containing nickel aluminide

The difficulties encountered in fabricating Ni₃Al-based intermetallic alloys into final structural components, due to their limited workability as a result of their inherent high yield strength and low ductility at elevated temperatures, are an important issue that have restricted the commercial applications of these materials. The Osprey spray deposition process is capable of delivering near-net-shape preforms, thereby avoiding the technical problems related to the hot working of these materials, e.g. hot rolling of slabs. The present work concerns an investigation of the cold rollability of a chromium-containing Ni₃Al intermetallic alloy produced with the Osprey process. The sliced preform with a thickness of 7 mm was successfully cold rolled through multipasses into sheets with a thickness of 0.7 mm and a good surface finish. The material has been found to have a high working hardening rate at room temperature. The maximum total reduction permissible without resulting in rolling defects is 30%. Thus, for larger reductions, intermediate annealing between rolling passes is necessary and it has been optimized to be at 1100°C for one hour. The repeated cold rolling and the recrystallization occurring during intermediate annealing change the initial microstructural features and grain size of the Osprey-spray-deposited material. The cold-worked and annealed intermetallic sheets with a thickness of 0.7 mm have a yield strength of 570 and 730 MPa and a elongation value of 33 and 7%, at room temperature and at 700°C, respectively. Fractography shows a transition from the transgranular fracture mode at low temperatures to the intergranular fracture mode at temperatures above 650°C.     

轧制复合三层铝合金板变形规律及力学性能的研究

采用"热轧+中间退火+冷轧+轧后退火"法复合轧制AA1100/AA7075/AA1100三层铝合金板。利用金相、SEM-EDS观察微观组织变化及界面元素扩散,由显微硬度和拉伸试验测定复合板力学性能。结果表明,AA7075层组织呈拉伸纤维状沿轧向分布;热轧包覆率不变,中间退火后包覆率随冷轧应变的增加先减小后几乎不变;结合界面处存在Mg、Zn元素扩散。轧后退火使复合板强度降低、塑性增加,硬度沿厚度方向呈现梯度变化规律。     

Proposal of bond criterion for hot roll bonding and its application

The aim of this work was to develop a bond criterion for laminated composites prepared by hot rolling. 7075 Al/AZ31B Mg/7075 Al laminated composites were fabricated by hot rolling at different reduction ratios and temperatures, and the hot rolling process was also simulated by finite element methods (FEM). The FEM results show that two stages existed for an option position of the interface during hot rolling, viz. the bonded interface forming period and the post-bonded period. Bonded interface would be damaged during the latter due to second tensile stress and tear stress (due to the sticking friction between the Al plates and the rollers during the rolling). A bond criterion for laminated composites fabricated by hot rolling was proposed, which includes a strain threshold and a critical bonding strength. The predicted bond results of the 7075 Al/AZ31B Mg/7075 Al laminated composite fabricated by hot rolling from the proposed bond criterion agreed with the experimental data.