Investigation of Bonding Behavior of AA1050/AA5083 Bimetallic Laminates by Roll Bonding Technique

In this study, 1-mm AA1050/AA5083 bimetallic laminates were produced using roll bonding (RB) process. The RB process was carried out with thickness reduction ratios of 25, 50 and 75%, separately. Finite element simulation was used to model the deformation of bimetallic laminates for various experimental conditions. Particular attention was focused on the bonding of the interface between AA1050 and AA5083 layers in the simulation. The optimization of thickness reduction ratios was obtained for improvement of the bond strength of bimetallic laminates during RB process. During the simulation, the mean equivalent strain at the interface zone between the layers was found to reach the maximum value with a high quality bond for the sample produced with 75% of thickness reduction. Moreover, the fracture surface of samples around the interface of laminates after the tensile test was studied to investigate the bonding quality by scanning electron microscopy.     

Microstructure and Mechanical Properties of AA5005/AA6061 Laminated Composite Processed by Accumulative Roll Bonding

The AA5005/AA6061 laminated composite has been fabricated by the accumulative roll bonding (ARB) using commercial AA5005 and AA6061. In the ARB process, one piece of AA5005 sheet and one piece of AA6061 sheet were stacked together and rolled with a 50 pct reduction without any lubrication. The materials were heated at 473 K (200 °C) for 10 minutes before each rolling process and were deformed up to four cycles to accumulate an equivalent strain of 3.2 and form an AA5005/AA6061 laminated composite. Mechanical properties and microstructure of the laminated composites were tested. The hardness and tensile strength increased, and the grain size reduced with the number of ARB cycles. Ultrafine grains elongated along the rolling direction were developed during the ARB process. The thicknesses of the grains of both the AA5005 and AA6061 layers were less than 200 nm after the fourth cycle. The uniform elongation decreased drastically after the first cycle ARB and stayed almost unchanged after further ARB process. The hardness of the AA5005 layer was slightly lower than that of the AA6061 layer. The microstructures from optical microscope and transmission microscope showed that in the AA6061 layer large precipitates in the micron scale and small particles less than 100 nm were present, whereas in the AA5005 layer there were large scale precipitates, but no small-sized particles.     

Evaluation of Mechanical Properties and Structure of Al-1100 Composite Reinforced with ZrO<Subscript>2</Subscript> Nanoparticles via Accumulative Roll-Bonding

In this study, aluminum metal matrix composites reinforced with ZrO₂ nano-particles in volume fraction of 0.5, 0.75 and 1 % were manufactured through accumulative roll bonding (ARB) process. The results of composite microstructure indicated excellent ZrO₂ particle distribution in the Al matrix after 10 cycles of ARB process. The X-ray diffraction results also showed that nanostructured Al/ZrO₂ nano-particles composite with the average crystallite size of 48.6 nm was successfully achieved after 10 cycles of ARB process. The tensile tests were conducted on the ARBed strips. The tensile strength increased 2.15 times more than the initial value. The elongation dropped abruptly at the first cycle, and then increased slightly. The SEM images observations from the fracture surface showed that after 10 cycles of ARB process the fracture was almost shear fracture mode with fine and stretched pores.     

Producing of AA5083/ZrO2 Nanocomposite by Friction Stir Processing (FSP)

In this study, friction stir processing (FSP) was used to produce AA5083/ZrO₂ nanocomposite layer. Optical microscopy and SEM were used to probe the microstructures formed in the composite layer. In addition, the mechanical properties of each sample are characterized using both tensile and hardness tests. Results showed that FSP is an effective process to fabricate AA5083/ZrO₂ nanocomposite layer with uniform distribution of ZrO₂ particles, good interfacial integrity, and significant grain refinement. On processing, in the proper combination of process parameters, the metal matrix composite layer was observed to have increased tensile and hardness properties.     

Failure mechanisms in superplastic AA5083 materials

The mechanisms of tensile failure in four 5083 aluminum sheet materials are evaluated under conditions of interest for superplastic and quick-plastic forming. Two mechanisms are shown to control failure of the AA5083 materials under uniaxial tension at elevated temperatures: cavitation and flow localization (i.e., necking). Conditions for which failure is controlled by cavitation correspond to those under which deformation is primarily by grain-boundary-sliding creep. Conditions for which failure is controlled by flow localization correspond to those under which deformation is primarily by solutedrag creep. A geometric parameter, Q, is used to determine whether final failure is controlled by cavitation or by flow localization. Differences in elongations to failure between the different AA5083 materials at high temperatures and slow strain rates are the result of differences in cavitation behaviors. The rate of cavitation growth with strain is nearly constant between the AA5083 materials for identical testing conditions, but materials with less tensile ductility evidence initial cavitation development at lower strain levels. The rate of cavitation growth with strain is shown to depend on the governing deformation mechanism; grain-boundary-sliding creep produces a faster cavitation growth rate than does solute-drag creep. A correlation is found between the early development of cavitation and the intermetallic particle-size population densities of the AA5083 materials. Fine filaments, oriented along the tensile axis, are observed on fracture surfaces and within surface cavities of specimens deformed primarily under grain-boundary-sliding creep. As deformation transitions to control by solute-drag creep, the density of these filaments dramatically decreases.     

Gallium-induced magnesium enrichment on grain boundary and the gallium effect on degradation of tensile properties of aluminum alloys

By applying a controlled amount of gallium (3 mg or 5 mg) to double-notched samples, the effects of the gallium on the grain boundary chemistry and tensile properties of AA6061-T4 alloy were investigated. Commercial-purity aluminum AA1050 was used for comparison to determine whether alloying elements would correlate with Ga-induced embrittlement and to elucidate the physical reason that governed the occurrence of intergranular fracture in the AA6061 Al-Mg-Si alloy. The AA6061 and AA1050 samples wetted by 3 mg or 5 mg of Ga were held statically for 7 days before tensile tests were conducted. The 6061 Al-Mg-Si samples with gallium were fractured intergranularly. However, the Ga-treated AA1050 samples had a mixed fracture mode, showing better strength and ductility than the Ga-treated AA6061 alloy, independent of whether the samples had their longitudinal axis parallel or perpendicular to the rolling direction, or the holding temperatures before tensile tests. Auger electron spectroscopy scanning the intergranular facets on fracture surfaces showed that the Auger peak-to-peak ratio I_Ga/I_Al of 6061 samples was similar to that of 1050 samples, but the high intensity of Mg signal was detected from the intergranular fracture surface of the AA6061 alloy. Magnesium being induced by Ga to enrich on the grain boundary and free surface of the AA6061 alloy was confirmed. The intergranular embrittlement of the 6061 T4 Al-Mg-Si alloy wetted by small amount of Ga involves the combination of the following two effects: Ga metal on grain boundary embrittlement, and Ga-induced magnesium enrichment on grain boundary that further decreases the strength of the grain boundary.     

Effect of Operation Parameters on Diffusion Bonded AA5083, AA6082 and AA7075 Aluminum Alloys

Rolled plates of 5 mm thick AA5083, AA6082 and AA7075 aluminum alloys Joints were fabricated by diffusion bonding at different temperatures. The microstructure evolution of AA5083, AA6082 and AA7075 aluminium alloys were characterized by transmission electron microscopy. Metallurgical investigations and mechanical tests were also performed to correlate the microstructural investigations with the mechanical properties of the produced diffusion bonded joints. It was observed that the bonding and shear strength increased with the increase in bonding temperature due to the diffusion of micro-constituents in the interface. Higher temperature enhanced the uniform distribution of secondary phase particles, which further improved the reduction in pores/defects in the bonded joints.     

An Investigation of Interface Bonding of Bimetallic Foils by Combined Accumulative Roll Bonding and Asymmetric Rolling Techniques

The bond strength in bimetallic materials is an important material characteristic. In this study, 0.1-mm thick bimetallic foils (AA1050/AA6061) were produced using one pass of accumulative roll bonding followed by three passes of asymmetric rolling (AR). The AR passes were carried out at roll speed ratios of 1.0, 1.1, 1.2, 1.3, and 1.4 separately. Finite element simulation was used to model the deformation of the bimetallic foils for the various experimental conditions. Particular attention was focused on the bonding of the interface between AA1050 and AA6061 layers in the simulation. The optimization of the roll speed ratio was obtained for improvement of the bond strength of the interface of AA1050/AA6061 bimetallic foils during AR process. In the simulation, the mean equivalent strain at the interface zone between the AA1050 and AA6061 layers was seen to reach a peak value at a roll speed ratio of about 1.2 to 1.3, which also corresponded to a high quality bond at the interface as observed experimentally.     

Fabrication of High-Strength Al/SiC<Subscript><Emphasis Type="Italic">p</Emphasis></Subscript> Nanocomposite Sheets by Accumulative Roll Bonding

Accumulative roll bonding (ARB) was successfully used as a severe plastic deformation method to produce Al-SiC nanocomposite sheets. The effects of process pass and amount of SiC content on microstructure and mechanical properties of the composites are investigated. As expected, production of ultrafine grain structures by the ARB process as well as nanosize particulate reinforcements in the metal matrix composite (MMC) resulted in excellent mechanical properties. According to the results of the tensile tests, it is shown that the yield and tensile strengths of the composite sheet increased with the number of ARB cycles without saturation at the last cycles. Scanning electron microscopy (SEM) revealed that the particles had a random and uniform distribution in the matrix by the last ARB cycles, and strong mechanical bonding takes place at the interface of the particle matrix. Transmission electron microscopy (TEM) and the corresponding selected area diffraction (SAD) demonstrate ultrafine grains with large misorientation in the structure. It is also shown that by increasing the volume fraction of particles up to 3.5 vol pct, the yield and tensile strengths of the composite sheets increased more than 1.3 and 1.4 times the accumulative roll-bonded aluminum sheets, respectively.     

Microstructural characterization of dissimilar friction stir welds between AA2219 and AA5083

Fusion welding of dissimilar aluminum alloys is very challenging. In the present work, Al-Cu alloy AA2219-T87 was friction stir welded to Al-Mg alloy AA5083-H321. Weld microstructures, hardness, and tensile properties were evaluated in as-welded condition. Microstructural studies revealed that the nugget region was primarily composed of alloy 2219, which was placed on the advancing side. No significant mixing of the two base materials in the nugget region was observed. Hardness studies revealed that the lowest hardness in the weldment occurred in the heat-affected zone on alloy 5083 side, where tensile failure were observed to take place. Tensile tests indicated a joint efficiency of around 90%, which is substantially higher than what can be achieved with conventional fusion welding. Overall, the results show that satisfactory butt welds can be produced between AA2219-T87 and Al-Mg alloy AA5083-H321 sheets using friction stir welding.     

Effect of Welding Parameters on Microstructure,Thermal, and Mechanical Properties of Friction-Stir Welded Joints of AA7075-T6 Aluminum Alloy

A high-strength Al-Zn-Mg-Cu alloy AA7075-T6 was friction-stir welded with various process parameter combinations incorporating the design of the experiment to investigate the effect of welding parameters on the microstructure and mechanical properties. A three-factors, five-level central composition design (CCD) has been used to minimize the number of experimental conditions. The friction-stir welding parameters have significant influence on the heat input and temperature profile, which in turn regulates the microstructural and mechanical properties of the joints. The weld thermal cycles and transverse distribution of microhardness of the weld joints were measured, and the tensile properties were tested. The fracture surfaces of tensile specimens were observed by a scanning electron microscope (SEM), and the formation of friction-stir processing zone has been analyzed macroscopically. Also, an equation was derived to predict the final microhardness and tensile properties of the joints, and statistical tools are used to develop the relationships. The results show that the peak temperature during welding of all the joints was up to 713 K (440 °C), which indicates the key role of the tool shoulder diameter in deciding the maximum temperature. From this investigation, it was found that the joint fabricated at a rotational speed of 1050 rpm, welding speed of 100 mm/min, and shoulder diameter of 14 mm exhibited higher mechanical properties compared to the other fabricated joints.     

Enhancement of the Stress Corrosion Sensitivity of AA5083 by Heat Treatment

In this study, the stress corrosion cracking (SCC) resistance of AA5083 is intentionally degraded by a series of progressively longer annealing treatments at 448 K (175 °C) that create a two-phase microstructure. Precipitation of strongly anodic Mg₂Al₃, known as β-phase, occurs heterogeneously with substantial precipitation along the grain boundaries, as observed by differential interference microscopy. Ultimate tensile strength, yield strength, and strain to failure of AA5083 alloy were found to be independent of the amount of β-phase precipitates, making AA5083 an ideal system to study the relative contributions of anodic dissolution and hydrogen embrittlement. Open circuit dropwise exposure SCC tests with precracked double cantilever beam (DCB) specimens made from the AA5083 alloy with different heat treatment conditions were conducted using 3.5 pct NaCl solution at an initial stress intensity factor (K _I ) of \( 1 5\,{\text{ksi}}\sqrt {\text{in}} .\;\left( { 1 6. 5\,{\text{MPa}}\sqrt {\text{m}} } \right). \) Two SCC characteristics, initial crack growth rate and incubation time, were found to be strongly dependent on the amount of β-phase precipitates. Initial crack growth rate increased sigmoidally as a function of heat treatment time with an inflection point between 120 and 240 hours of sensitization time, while the incubation time decreases monotonically with sensitization time. Additionally, fracture surfaces investigated by scanning electron microscopy demonstrated characteristics of intergranular cracking with multiple crack tips. Discussion centers on the evidence supporting anodic dissolution of β-phase grain boundary precipitates as a primary mechanism of SCC in severely sensitized AA5083 alloy and the potential contribution of hydrogen embrittlement in the failure of grain boundary ligaments between β-phase grain boundary precipitates in less severely sensitized conditions.     

Deformation textures of AA8011 aluminum alloy sheets severely deformed by accumulative roll bonding

A fully annealed AA8011 aluminum alloy sheet containing a number of large particles (∼5 μm) was severely deformed up to an equivalent strain of 12 by an accumulative roll-bonding (ARB) process. The texture evolution during the ARB process was clarified, along with the microstructure. The ARB-processed aluminum alloy sheets had a different texture distribution through the sheet thickness, due to the high friction between the roll and the material during the ARB process. The shear textures composed of {001} 〈110〉 and {111} 〈110〉 orientations developed at the sheet surface, while the rolling textures, including Cu {112} 〈111〉 and Dillamore {4,4,11} 〈11,11,8〉 orientations, developed at the sheet center. The textural change from a shear texture to a rolling texture at the sheet center during the ARB process contributed to an increase in the fraction of high-angle boundaries. Also, a large number of second-phase particles in the AA8011 alloy sheets weakened the texture. Up to the medium strain range (below ɛ=6.4), relatively weak textures developed, due to the inhomogeneous deformation around the second-phase particles; after the strain of 6.4, strong rolling-texture components, such as the Dillamore and Cu orientations, developed. This remarkable textural change can be explained by the reprecipitation of fine particles in grain interiors.     

Analysis of Strain Rate Sensitivity of Ultrafine-Grained AA1050 by Stress Relaxation Test

Commercially pure aluminum sheets, AA 1050, are processed by accumulative roll bonding (ARB) up to eight cycles to achieve ultrafine-grained (UFG) aluminum as primary material for mechanical testing. Optical microscopy and electron backscattering diffraction analysis are used for microstructural analysis of the processed sheets. Strain rate sensitivity (m-value) of the specimens is measured over a wide range of strain rates by stress relaxation test under plane strain compression. It is shown that the flow stress activation volume is reduced by decrease of the grain size. This reduction which follows a linear relation for UFG specimens, is thought to enhance the required effective (or thermal) component of flow stress. This results in increase of the m-value with the number of ARB cycles. Strain rate sensitivity is also obtained as a monotonic function of strain rate. The results show that this parameter increases monotonically by decrease of the strain rate, in particular for specimens processed by more ARB cycles. This increase is mainly linked to enhanced grain boundary sliding as a competing mechanism of deformation acting besides the common dislocation glide at low strain rate deformation of UFGed aluminum. Recovery of the internal (athermal) component of flow stress during the relaxation of these specimens seems also to cause further increase of the m-value by decrease of the strain rate.     

累积叠轧焊制备超细晶IF钢微观组织与力学性能

采用累积叠轧焊方法制备了超细晶IF钢，对其微观组织和力学性能进行了分析。实验结果表明，累积叠轧后IF钢的平均晶粒尺寸为700nm；抗拉强度为621．3MPa，达到冷轧IF钢抗拉强度的2．02倍，屈强比σ0.2/σb为0．81。在累积叠轧过程中产生的氧化物夹杂导致超细晶IF钢的脆化。     

Microstructural evolution and mechanical properties of the AA8011 alloy during the accumulative roll-bonding process

The investigation of the microstructure and mechanical properties has been conducted on an AA8011 alloy produced by a novel intense plastic straining process named accumulative roll bonding. The results show that an ultrafine-grained 8011 alloy, having a mean grain (or subgrain) size less than 1 μm, was successfully accumulative roll-bonded (ARB) at room temperature (RT-ARB) and at 200 °C (HT-ARB). The average grain (or subgrain) sizes of the RT-ARB and HT-ARB samples were reduced greatly from about 25.8 μm initially to 650 to 700 nm and 800 to 900 nm, respectively. After several cycles of accumulative roll bonding, most regions of this material were filled with ultrafine grains with high-angle boundaries. The ambient tensile strengths of the RT-ARB and HT-ARB samples increased with equivalent strain only up to the strain of 2.4. After that, the strengths of the RT-ARB samples nearly leveled off, and the strengths of the HT-ARB samples decreased with equivalent strain above the strain of 2.4. Furthermore, the elongation in both the RT-ARB and HT-ARB samples decreased greatly after the first cycle and then increased continuously with strain. The softening behavior happened in HT-ARB samples above a strain of 2.4, which is mainly attributed to the continuous recrystallization, dynamic recovery, and static recovery during and/or after the accumulative roll-bonding process.     

5083合金不同均质制度的组织和性能研究对比

采用光学金相显微镜、拉伸试验机、SEM及EDS等分析手段,对比分析5083合金不同均质制度下微观组织、力学性能及拉伸断口形貌.研究结果显示,5083合金均质处理后,枝晶组织消除,初生相部分回溶到基体中,弥散相均匀析出,起到一定的弥散强化作用,强度和塑性均优于铸态;未均质铸锭以脆性断裂为主,均质处理的铸锭断裂方式为韧性断...     

Deformation and failure of a superplastic AA5083 aluminum material with a cu addition

A modified AA5083 aluminum sheet material containing a Cu addition of 0.61 wt pct has been investigated under conditions relevant to commercial hot-forming technologies. This material was produced by continuous casting followed by industrial hot and cold rolling into sheet. Deformation and failure mechanisms at elevated temperatures were investigated through mechanical testing, thermal analysis, and microscopy. The effects of Cu addition are evaluated by comparisons with data from AA5083 sheet materials without Cu addition, produced both by continuous and direct-chill (DC) casting techniques. At low temperatures and fast strain rates, for which solute-drag (SD) creep governs deformation, the Cu addition slightly increases tensile ductility at 450 °C but does not otherwise alter deformation behaviors. At high temperatures and slow strain rates, for which grainboundary-sliding (GBS) creep governs deformation, the Cu addition decreases flow stress and, at 450 °C, improves tensile ductility. A strong temperature dependence for tensile ductility results from the Cu addition; tensile ductility at 500 °C is notably reduced from that at 450 °C. The Cu addition creates platelike particles at grain boundaries, which produce incipient melting and the observed mechanical behavior.     

Constitutive behavior of as-cast AA1050, AA3104, and AA5182

Recent thermomechanical modeling to calculate the stress field in industrially direct-chill (DC) cast-aluminum slabs has been successful, but lack of material data limits the accuracy of these calculations. Therefore, the constitutive behavior of three aluminum alloys (AA1050, AA3104, and AA5182) was determined in the as-cast condition using tensile tests at low strain rates and from room temperature to solidus temperature. The parameters of two constitutive equations, the extended Ludwik equation and a combination of the Sellars-Tegart equation with a hardening law, were determined. In order to study the effect of recovery, the constitutive behavior after prestraining at higher temperatures was also investigated. To evaluate the quantified constitutive equations, tensile tests were performed simulating the deformation and cooling history experienced by the material during casting. It is concluded that both constitutive equations perform well, but the combined hardening-Sellars-Tegart (HST) equation has temperature-independent parameters, which makes it easier to implement in a DC casting model. Further, the deformation history of the ingot should be taken into account for accurate stress calculations.