Preparation and characterization of aluminium alloy sheet Aramid fibre-laminated composites

Laminated composites consisting of alternate layers of aluminium alloy sheets and unidirectional Kevlar-49 fibre epoxy composites were prepared using two different aluminium alloys DTD 687 and aluminium-lithium alloy. Tensile, compressive and interlaminar shear strengths of the laminates were measured. The residual stresses in the aluminium alloy sheets arising out of thermal mismatch between aluminium alloys and aramid fibres were also measured. It is found that the laminates have lower density, higher tensile strength and marginally lower Young’s modulus as compared with monolithic alloy sheets.     

Interface sheet-constrained groove pressing as a modified severe plastic deformation process

In this paper, a new severe plastic deformation (SPD) process entitled interface sheet-constrained groove pressing (ISCGP) as a new variant of conventional CGP has been developed for producing ultrafine-grained metallic materials. In this process, repetitive shear deformation is imposed into the sheet material by utilising symmetrically grooved die along with two interface sheet on both sides. To study the applicability, mild steel sheets were processed by both ISCGP and CGP processes, and mechanical and microstructural properties of the processed samples were investigated. The results show a considerable improvement in mechanical properties including hardness, yield strength, and ultimate tensile strength, though the ductility sacrifice was reduced. Comparing ISCGP and conventional CGP revealed interesting results, which are shown that ISCGP can result in better surface quality and ductility.     

Car body alloys and methods of corrosion protection: Aluminium Sheet

The aluminium industry supplies various car body sheet qualities tailor-made to meet the requirements of the car producers. The most important alloy types are AlMgSi (free from stretcher-strain markings after forming and hence suited for outer skin) and AlMg (for interior use). In addition to the significant weight savings it is its long service life which makes aluminium an attractive alternative to steel sheets. A prerequisite for good corrosion resistance is a surface treatment optimised for aluminium. This includes the creation of a phosphate surface layer to allow lacquer coating together with steel and galvanized steel on existing lines. The Accelerated Outdoor Exposure Test (VDA 621–414) proved to be the only static corrosion test method suitable for assessing the resistance level of the final lacquered car body. In addition to the proper selection of alloy and surface finishing technique it is important that some aluminium-specific precautions are taken during manufacture if the full long service potential of the material is to be realized.     

Formability of continuous cast 5052 alloy thin sheets

The formability of continuous cast 5052 alloy thin sheets from two different process schedules was examined. One was prepared in the laboratory by cold-rolling from a continuous cast thick plate followed by annealing (lab-processed sheet), and the other was produced by a new process involving hot-rolling followed immediately by in-line annealing (in-line annealed sheet). Tensile test results indicate that all the lab-processed sheets exhibit evident yield behavior. Increasing rolling reduction results in an increase of strength and a decrease of ductility in the lab-processed sheets due to increasing contribution of centerline segregation of second-phase particles. Both the lab-processed sheets annealed at 400 °C for 90 min and the in-line annealed sheets exhibit tensile elongation of more than 20% and two-stage strain hardening behavior. Compared with the lab-processed sheets, the in-line annealed sheet annealed at 454 °C has higher values of UTS and elongation. Furthermore, forming limit curves were determined. It is found that the level of the forming limit curve of the lab-processed thin sheet is lower than that of conventionally produced 5052-O Al, but close to that of 6111-T4 Al sheet. Moreover, the in-line annealed sheets have higher limit strains than the lab-processed sheets. These results demonstrate that the in-line annealing process results in the production of continuous cast alloy sheet with improved formability.     

In-plane anisotropy in tensile deformation and its influence on the drawability of Nimonic c–263 alloy sheets

An effort has been made to comprehensively evaluate and rationalize the in-plane anisotropy in tensile properties and the effect of aging on the nature of deformation (strain hardening behaviour) and formability characteristics, especially the limit drawing ratio and forming limit diagram. Despite weak crystallographic texture and excellent ductility and high work hardening exponents, the alloy sheets of C-263 exhibit significant extent of in-plane anisotropy in its tensile properties and yield loci. The absolute magnitudes of yield stress and the exact nature of anisotropy that can be predicted from the tensile part of the yield locus need to be employed with caution. This is because when the magnitudes of the yield stresses, obtained from yield locus are more than 5 times higher as compared to the yield and ultimate tensile strength values and the nature and degree of in-plane anisotropy under tensile loading matches with that of only the compressive yield stresses of yield locus. The alloy sheet, due to weak crystallographic texture and relatively high strengths, is found to be far more suitable for structural applications, rather than for deep drawing applications, which was reflected in low limit drawing ratio values (1.34 for CR+ST and 1.23 for peak aged conditions). Further, the study conducted reveals that the safer forming limits in strain space is higher for CR+ST condition; while, the safer forming limits in stress space are higher for peak aged (CR+ST+1073 K/8 h) condition. Finally, detailed studies are outlined to arrive at suitable microstructural and textural characteristics that provide significantly enhanced drawability in the Nimonic C-263 alloy sheets.     

Tailoring materials properties of UFG aluminium alloys by accumulative roll bonded sandwich-like sheets

Accumulative roll bonding (ARB) as a method of severe plastic deformation is a well-established process to produce ultrafine-grained (UFG) sheet materials with extraordinary mechanical properties. In this work ARB is applied to combine different sheet materials in order to tailor the materials properties by producing sandwich-like structures. The high strength aluminium alloy AA5754, after 4 ARB cycles (N4), is used as a core material. To achieve high corrosion resistance and good visual properties, it is cladded with commercially pure aluminium AA1050A (N4) at room temperature and alternatively with AA6014 (N4) at 230 °C. All materials are UFG and satisfactory bonding between the different layers of aluminium alloys is achieved. Nanoindentation measurements reveal that there is a sharp transition in hardness at the interface. The yield and tensile strength of the core material are fully retained in the case of the AA6014/AA5754 sandwich. The strength of the AA1050A/AA5754 sandwich is slightly lower compared to the core material but still twice as high as the clad material. The serrated yielding effect which is strongly visible in tensile tests on the pure AA5754 alloy completely disappears in the sandwich sheets, which means the surface quality is strongly enhanced.     

Effects of zinc coating on magnesium alloy–steel joints produced by cold metal transfer method

Magnesium alloys are lap-joined to galvanised and bare steel sheets by a cold metal transfer method. The weld appearance, cross-section, tensile strength and fracture behaviour of these joints are characterised by scanning electron microscopy, tensile tests and energy-dispersive spectroscopy. The joints were found to have good weld appearance and satisfactory tensile strength. The spreadability and wettability of the Mg alloy–galvanised steel joint are superior to those of the Mg alloy–bare steel joint, but the tensile strength is lower. In particular, the presence of Zn on the galvanised steel sheet improves wettability but decreases tensile strength. Aluminium has a high affinity for Fe, and the thinner layer of Fe–Al improves the mechanical properties of the Mg alloy–bare steel joint.     

Temperature dependence of the tensile behaviour of aramid/aluminium laminates

Aramid/aluminium laminates (ARALL^® laminates) are a family of new hybrid composites made of alternating layers of thin aluminium alloy sheets with plies of epoxy adhesive prepreg containing unidirectional aramid fibres. The effect of elevated and cryogenic temperatures on these materials is critical to aerospace applications. ARALL 1, 2, 3, and 4 laminates have been tested in tension at temperatures ranging from –300F–400 °F (–184–204 °C) and at room temperature after exposure. This paper summarizes how tensile properties depend on temperature for these four ARALL laminates under the conditions described. At cryogenic temperatures, no degradation of ultimate tensile strengths, tensile yield strengths and moduli were found for either the longitudinal or transverse directions for ARALL 1–4 laminates. Furthermore, the mechanical properties remained the same or increased slightly as the temperature decreased. Longitudinal and transverse ultimate tensile strengths, tensile yield strengths, and moduli of ARALL 1–3 laminates at room temperature remain nearly constant after the laminates were exposed for 1, 10 and 100 h to temperatures up to 250 °F (121 °C), and up to 350 °F (177 °C) for ARALL 4 laminates. However, these properties determined at the elevated temperatures after 1, 10 and 100 h exposure showed a tendency to decrease with increasing temperature. The properties of ARALL laminates are much better in the longitudinal fibre direction than those of conventional monolithic aluminium alloys. Typical failure modes of the test specimens in the high-temperature range were examined using a scanning electron microscope. The discussions are also described in the paper.     

Mechanical Properties and Corrosion Resistance of Nitrided or Oxinitrided,and Powder Painted Regular and Interstitial Free (IF) Drawing Steel Sheet

Specimens of 0.8 mm thick regular and interstitial free (IF) drawing steel sheet have been nitrided in fluidised bed for 2 hours at 620 °C and 560 °C with and without a post‐oxidation, and slow and accelerated cooling. As a result, surface hardness, yield and tensile strength of the sheets increased considerably without a critical loss of ductility. Resistance welds between the sheets did not lose their original strength after nitriding‐oxinitriding. Nitrided‐oxinitrided at 620 °C and then powder painted sheets, as compared with powder painted raw sheets, were more corrosion resistant in neutral salt spray and climatic tests. Some mechanical and anticorrosion properties of the IF steel sheet that had undergone the nitriding‐oxinitriding processes were definitely better than those of equally processed regular steel sheet.     

Effect of annealing on formability of aluminium grade 19000

Forming limit diagrams are used by the stampers to solve sheet metal forming problems. In practice, sheet metals have been subjected to various combinations of strain. Necking during sheet metal forming, sets the limit to which the sheet metal can be formed. Forming limit diagram is an effective tool to evaluate the formability of sheet metal in various strain conditions. The information upon the formability of the sheet metal is important for both sheet metal manufacturers and users. In this work, a study has been made on the formability of aluminium 19000 grades annealed at three different temperatures namely 160 °C, 200 °C and 300 °C for sheet thickness of 2.00 mm. The tensile properties and formability parameters were experimentally evaluated and they are related to forming limit diagram. Strain distribution profiles obtained from the forming experiment have been analyzed. The fractured surface of the formed samples were viewed using scanning electron microscope (SEM) and the SEM images were correlated with fracture behaviour and formability of sheet metal. The sheet which is annealed at 300 °C has been found to possess good drawability and stretchability compared to other two annealed sheets.     

Improvement of ductility in magnesium alloy sheet using laser scanning treatment

This paper suggests a novel method for improving the ductility of magnesium alloy sheets using a laser scanning treatment combined with a defocusing technique. The crystallographic orientation on both surface regions of the AZ31B magnesium alloy sheet processed using this method was changed from a strong basal texture to an almost random texture. The laser-scanned magnesium alloy sheet showed enhanced tensile elongation of up to 50% with a similar a tensile strength.     

Forming limit diagram for Indian interstitial free steels

In this work, the suitability of interstitial free steel sheets of thickness 0.6 and 1.6 mm for press forming operations were examined by obtaining the forming limit diagram. The microstructural aspects, tensile properties and formability parameters were studied. Forming limit diagrams (FLD) were evaluated for the above sheet metals of two different thicknesses and they were compared. Strain distribution profiles were obtained from the forming experiment. The fracture surfaces of the formed samples were observed using scanning electron microscope. Using the fractography, the fracture behaviour and formability were analyzed. The tensile properties and formability parameters were correlated with the FLD. It was found that the formability of both sheets is good and the sheet with 1.6 mm thickness was superior.     

Microstructure and mechanical properties of Mg–Al–Zn alloy sheets severely deformed by accumulative roll-bonding

The as-rolled AZ31 Mg alloy sheets were subjected to accumulative roll-bonding (ARB) at 300 °C up to three cycles. The microstructure and macro- texture are investigated by means of optical microscopy and X-ray analysis. The mechanical properties are evaluated by micro-hardness and tensile tests. Very fine grain size of 2.4 μm could be achieved after three passes of 50% thickness reduction. The recrystallized structure was already formed after one cycle of ARB. ARB processing resulted in a significant increase of ductility and slight decrease of tensile strength of the AZ31 alloy sheet. Basal texture was notably weakened after ARB processing.     

镁合金塑性成形性能实验与数值模拟研究

对ME20M镁合金板料进行了热拉深成形性能实验与数值模拟.研究表明,ME20M镁板热拉深成形极限高度随实验参数的不同而不同,其塑性成形性能随温度的升高明显改善;数值模拟可以很好地预测不同实验参数下镁合金板料热拉深成形极限的高度.对热拉深成形件传力区部位进行金相实验得知,合理控制热拉深实验参数能保证镁合金塑性成形件微观组织,进而保证成形件质量.     

工艺参数对7075铝合金板材时效成形性的影响

为评价7075铝合金板材的可时效成形性并掌握最佳的时效成形工艺参数,基于机械加载时效成形试验工装,开展了时效温度和时间对7075铝合金板材时效成形后构件力学性能和物理性能影响的试验研究.结果表明:7075铝合金板材的时效成形性与工艺参数密切相关,随着时效温度和时间的增大,板材的电导率呈升高趋势,而其拉伸性能则呈降低趋势;且合金的拉伸断裂方式与时效状态有关,过时效初期以沿晶韧窝和穿晶韧窝混合型断裂为主,随着过时效进行主要为韧窝断裂.综合考虑构件时效成形后拉伸性能和电导率等情况,合金最佳时效温度为180℃,且保温时间不宜长于16 h.     

Modelling of electro hydraulic free and die forming of sheet steels

Electro hydraulic forming of a range of different sheet steels was studied experimentally and with finite element methods. Four carbon and stainless sheet materials were studied. In this paper we present results on a mild steel (IF210), two high strength steels (DPX800 and TRIP700) and one stainless steel (1.4509). The flow properties of the materials were evaluated at a range of strain rates up to 1000/s. These were typical strain rates in the FE simulations. The flow properties were characterized with the Johnson Cook model. Electro hydraulic forming trails were performed with a chamber of water with a pair of electrodes on one side of the sheet. In one case free forming was performed and in the other case forming was performed into a truncated conical die. Geometrical shapes and strain distributions were evaluated after forming. A finite element model was formulated in ABAQUS explicit. The model takes the chamber filled with water into account and the effect of the electrical discharge is modeled as a pressure wave originating from the location of the electrodes. The sheet is given the properties defined by the Johnson Cook model and stiff tools are used. The forming of the sheet is described including rebound effects at the tools. The model shows satisfactory results in relation to the experimental trials regarding both shape and strains of the pressed sheets.     

Formability and numerical simulation of AZ31B magnesium alloy sheet in warm stamping process

The potential process for mass production of magnesium alloy components in vehicles—warm stamping process was investigated systematically in the present study. For analyzing the forming process, an accurate numerical model describing the unique characteristics of magnesium alloy sheets under warm forming is very essential. Aiming at this, hardening/softening model for 1.5 mm thickness AZ31B magnesium alloy sheet were firstly constructed based on uniaxial tensile tests. Secondly, semispherical drawing was carried out under the selected temperature to generate experimental forming limit curve (FLC) for AZ31B sheet. Then, friction coefficient was identified using a high-temperature tribo-tester. Finally, numerical simulation was implemented and formability of AZ31B sheet warm forming was verified with experiment. The result shows that the formability, thickness distribution and equivalent strain distribution in simulation agreed well with the actual specimens, which thus provided a good data base for describing the unique characteristics of magnesium alloy sheets under warm forming.     

两道次成形过程中拉伸速度及热处理对2A12-O铝合金晶粒尺寸的影响

目的研究铝合金2A12材料在两道次变形过程中拉伸量、拉伸速度及热处理参数对材料晶粒尺寸的影响规律。方法进行了2A12-O铝合金板的"预拉伸-退火-再拉伸-淬火"两道次成形过程。当两次拉伸量相等,总拉伸量不大于20%时,研究了拉伸速度、退火温度、淬火保温时间与试验后晶粒尺寸的关系。结果在拉伸总量较小的情况下,拉伸速度和各热处理参数对材料最终晶粒尺寸的影响较大;当拉伸总量增大到某临界值时,拉伸速度和热处理参数的影响明显减小,各参数下的晶粒尺寸在总拉伸量相同的情况下趋于一致。结论获得了拉伸总量、拉伸速度、退火温度和淬火保温时间等成形及热处理参数对2A12-O铝合金板材晶粒尺寸的影响规律,为该材料成形及热处理过程中的晶粒尺寸控制提供了依据。     

An investigation on the bearing test procedure for fibre-reinforced aluminium laminates

Excellent fatigue, static strength and damage tolerance characteristics together with low density make fibre-reinforced aluminium laminates a prime candidate sheet material for application in fatigue- and fracture-critical aircraft structures. Their use requires that mechanical property design allowables be established for incorporation in design handbooks (e.g. MIL-HDBK-5). An experimental programme based on statistical design was conducted to establish a meaningful test procedure for determination of fibre-metal laminate bearing strength design allowables. The test procedures investigated are the pin-type bearing test method (ASTM E-238) and the bolt-type bearing test method, a modified method based on the procedure for bearing strength determinations in plastics (ASTM D-953). Results are presented from an experimental programme which measured the bearing strengths of two grades of S-2 glass-based and one grade of aramid-based aluminium laminates. The influences of lateral constraint and ply orientation on bearing strength and failure mode are shown. The bolt-type bearing test method, which combines the attributes of the two aforementioned methods, is recommended. The study also showed that the bearing properties for edge distance ratio e/D = 2 can be predicted by correlation with the aluminium volume fraction in fibre-reinforced aluminium laminates. In addition, diagrams of joint structural efficiency, shown to be comparable to those of aluminium alloy sheets, have been established.     

Tensile properties of stainless steel-clad aluminium sandwich sheet metals

The various tensile properties, such as yield strength, tensile strength, strength coefficient, uniform elongation, strain hardening exponent and strain rate sensitivities, of stainless steel-clad aluminium sandwich sheet metals have been analysed on the basis of the fact that the flow stresses of the sandwich sheets follow the rule of mixtures, an average of component properties weighted by the volume fractions. The rule of mixtures can be applied to the tensile strengths and strength coefficients of the sandwich sheets, whereas the yield strengths do not follow the mixture rule. The force weighted average rule, an average of component properties weighted by volume fractions and forces, can be applied to uniform elongations, strain hardening exponents and strain rate sensitivities of the sandwich sheets.