Microstructure-based finite element analysis of strain localization behavior in AA5754 aluminum sheet

A finite element (FE) analysis incorporating particles and grain structure is used to study the localization behavior of direct chill cast (DC) and strip cast (CC) AA5754 alloy sheet. A two-dimensional (2D) plane stress FE model is used to simulate deformation of a sample under uniaxial tension prior to necking. A 2D plane strain model is then used to simulate the post-necking behavior, up to fracture. The plane stress model shows that the strain required for the initiation of necking is similar in both materials, determined predominately by grain-level inhomogeneity, with constituent particles altering the localization path and localization strains, but only weakly. The plane strain model shows more through-thickness thinning during post-necking deformation of DC sheets compared with CC sheets. The CC material is also prone to shear-type failure, while the DC material exhibits a cup–cone-type failure. These differences arise from the microstructural difference between the two samples, where CC sheets contain more intermetallic particles in stringers compared with the DC sheets. This two-stage model is validated by experimental data which show similar limit strains in the DC and CC sheets but quite different fracture strains and fracture surface geometries.     

Shear Localization and Damage in AA5754 Aluminum Alloy Sheets

In this article, we study the Portevin-Le Chatelier (PLC) bands and their influences on strain localization and fracture in continuous cast (CC) AA5754 aluminum sheets. Three types of tensile tests are conducted: (1) tensile samples are pulled directly to fracture at 223 K, (2) tensile samples are pulled at 223 K to initiate diffuse necking followed by unloading and reloading to fracture at room temperature, and (3) tensile samples are pulled at 223 K to localized necking and unloaded followed by reloading to fracture at room temperature. Furthermore, in situ V-bending test coupled with deformation mapping using digital image correlation is used to study damage at large strains. The results show that PLC bands detect favorable geometrical sites for shear band initiation. The formation of shear bands precedes damage and damage is a consequence of shear band formation. This article was presented at Materials Science & Technology 2007, Automotive and Ground Vehicles symposium held September 16-20, 2007, in Detroit, MI.     

Mechanical properties and microstructure evolution in incremental forming of AA5754 and AA6061 aluminum alloys

This study performs single point incremental forming (SPIF) on two aluminum alloys (i.e. AA5754 and AA6061), and analyzes their post forming mechanical properties and microstructure evolution. The forming parameters namely wall angle (35°–55°), feed rate (1–4 m/min), spindle rotational speed (50–1000 r/min), and lubricant (grease and hydraulic oil) are varied to probe detailed processing effects. The pre- and post-SPIF mechanical properties and microstructures are characterized by conducting tensile tests and optical microscopy, respectively. It is shown that an increase in the wall angle, feed rate and rotational speed causes microscopic variations in the alloys such that the grains of AA5754 and the second phase particles of AA6061 elongate. As a result, the ultimate tensile strength of the formed parts is increased by 10% for AA5754 and by 8% for AA6061. And, the ductility of AA5754 is decreased from 22.9% to 12% and that of AA6061 is decreased from 16% to 10.7%. Regarding the lubricant effect, it is shown that the mechanical properties remain insensitive to the type of lubricant employed. These results indicate that SPIF processing modifies the microstructure of Al alloys in a way to enhance the strength at the cost of ductility.     

Investigation of Mechanical Properties and Fracture Simulation of Solution-Treated AA 5754

In this work, mechanical properties and fracture toughness of as-received and solution-treated aluminum alloy 5754 (AA 5754) are experimentally evaluated. Solution heat treatment of the alloy is performed at 530 °C for 2 h, and then, quenching is done in water. Yield strength, ultimate tensile strength, impact toughness, hardness, fatigue life, brittle fracture toughness \((K_{\text{Ic}} )\) and ductile fracture toughness \((J_{\text{Ic}} )\) are evaluated for as-received and solution-treated alloy. Extended finite element method has been used for the simulation of tensile and fracture behavior of material. Heaviside function and asymptotic crack tip enrichment functions are used for modelling of the crack in the geometry. Ramberg-Osgood material model coupled with fracture energy is used to simulate the crack propagation. Fracture surfaces obtained from various mechanical tests are characterized by scanning electron microscopy.     

AA1100铝箔的强韧化

采用光学显微镜、透射电镜和力学性能实验机等设备 ,研究了均匀化和成品工艺因素对AA1 1 0 0铝箔强韧性的影响。结果表明 ,材料经 560℃ ,1 6h均匀化处理和 2 30～ 2 60℃ ,1h退火处理后 ,σb≥ 1 2 0MPa ,δ≥2 0 % ,达到最佳的强韧化效果。同时对该材料的强韧化机理进行了探讨。     

An experimental and numerical study of prestrained AA5754 sheet in bending

This study focuses on the effects of prestrain magnitude on 3 mm AA5754 sheet in bending at nominal applied strain rates of 0.001/s and 0.1/s. The necessity of incorporating prestrain and strain rate effects into numerical simulations of bending is also evaluated. A series of experimental bend tests using axial compression in the longitudinal material direction were performed following plane strain prestrain in the transverse material direction. An inelastic buckling mode of deformation was produced with the peak buckling load increasing and the minimum load decreasing with larger magnitudes of prestrain. A semi-empirical material model, referred to as the Voce-MA model, was developed which incorporates strain rate-sensitivity of the flow stress, the prestrain magnitude and their interaction. Simulations of the bend tests using this material model were then performed in LS-DYNA at nominal applied strain rates of 0.001/s and 0.1/s for samples with 0, 3, 6 and 12% plane strain prestrain. It was shown that for AA5754 sheet in bending, prestrain effects must be considered in terms of current sheet thickness and material hardening. While the peak and minimum loads are not strain rate sensitive at the low rates used in this study, a rate-dependant material model is still necessary in order to account for the deviations in local strain rate from the applied strain rate. The Voce-MA material model was capable of representing prestrain and strain rate effects for all cases of AA5754 sheet in bending considered in this study.     

The Effect of Strain-Rate Sensitivity on Formability of AA 5754-O at Cold and Warm Temperatures

Aluminum-magnesium (Al-Mg) alloys have been widely used in diverse applications ranging from automotive bodies to food processing industries because of their excellent high-strength-to-weight ratio, corrosion resistance, and recyclability potential. The formability of these alloys is decreased at room temperature (RT) and is related with the strain-rate sensitivity. This study presents the effect of strain-rate sensitivity on formability of AA 5754-O alloy sheet at a test temperature range of −60 to 250 °C by duplicate tensile test at different strain rates. The test results indicated that the formability change with positive or negative strain-rate sensitivity values. It was observed that the strain-rate sensitivity values increased at negative temperatures with respect to RT. The best formability condition for this alloy in the test ranges was observed at 250 °C and 0.0016 s⁻¹.     

Influence of heat treatment and surface conditioning on filiform corrosion of aluminium alloys AA3005 and AA5754

The effect of high-temperature heat treatment combined with different cleaning and pre-treatment practices on filiform corrosion resistance has been investigated for aluminium alloys AA3005 and AA5754. High-temperature heat treatment severely reduces the filiform corrosion resistance of alloy AA3005, while the corrosion properties of alloy 5754 are only moderately affected. The drastic loss of filiform corrosion resistance of alloy AA3005 after high-temperature heat treatment is attributed to preferential microstructural changes in a heavily deformed, micrograined surface layer caused by large surface shear strain during rolling. The enhanced deformation of the near-surface region promotes precipitation of a fine dispersion of intermetallic particles during subsequent heat treatment. The higher density of intermetallic particles combined with lower supersaturated solid solution levels of manganese in the surface layer as compared to the bulk structure makes the heat-treated AA3005 material susceptible to superficial corrosion attacks and results in poor filiform corrosion resistance. Application of a commercial acid cleaning/chromating pre-treatment did not restore the filiform corrosion resistance of heat-treated alloy AA3005. Alloy AA5754, containing lower levels of manganese and iron than AA3005, did not undergo similar preferential microstructural changes during heat treatment. A moderate increase in the amount of filiform corrosion of heat-treated AA5754 samples is attributed to poor protective properties of the thick, magnesium enriched, thermally formed surface oxide on this alloy. Any cleaning/pre-treatment practice that removes the thermally formed oxide on this alloy results in a very high filiform corrosion resistance.     

Friction and wear at low temperatures

Metal Science and Heat Treatment -     

A correlation study of mechanical strength of resistance spot welding of AA5754 aluminium alloy

AA5754 aluminium alloy was resistance spot welded (RSW) to produce 27 different joint stack-ups with differing process parameters and corresponding weld quality. Quasi-static joint strength was evaluated for three test geometries; lap-shear, coach-peel and cross-tension. The results derived from over 1000 samples demonstrate various fundamental relationships. For lap-shear strength, a strong relationship with weld nugget diameter was observed; whilst discrete strength levels were found for coach-peel test geometry, depending on the governing metal thickness of the parent sheet for the various stack-ups. For cross-tension strength; there is a relationship with nugget diameter; but data are sensitive to nugget periphery defects. These fundamental relationships provide a set of generalised design guidelines for RSW of aluminium that will have significant relevance to manufacturing communities.     

Microstructural and Mechanical Characteristics of Aluminum Alloy AA5754 Friction Stir Spot Welds

In the present investigation, friction stir spot welding on annealed aluminum alloy AA5754 sheets was performed. The influences of the tool rotational speed and tool stirring (dwell) time on the weld structure and static strength of welds were evaluated. The results revealed that the width of the completely metallurgical-bonded region increases with the increasing tool rotational speed and/or the dwell time up to certain levels. Increasing such parameters beyond these levels slightly reduces the width of the bonding region. The stirred zone exhibited higher microhardness than that of the base material. The tensile-shear force was found to increase with the increasing tool rotational speed and/or dwell time up to a certain level (9s). Higher tool rotational speeds and/or prolonged dwell times slightly reduce(s) the tensile-shear force.     

Possibility of grain size prediction in AA5754 aluminium ingots using neural networks

Abstract

The approach to the grain size prediction in AA5754 Al alloy ingots based on artificial neural networks (ANN) has been used in the present study. The ANN has been trained on data that was measured in the real industrial conditions during the process of direct chill Al ingots casting. A very complex relation between the numerous casting parameters and the microstructure of the ingots justifies the application of neural networks, which are known for mapping complex and non-linear systems. A feed forward ANN model with the resilient back-propagation learning algorithm and weight decay regularisation has been developed to relate the grain size to casting rate, meniscus level, casting temperature, water flow for the metal mould cooling and speed of wire for master alloy addition. The results obtained from the ANN are found to be consistent with the theoretical researches and experience from the foundry.     

Thermal expansion of silicon at temperatures up to 1100 °C

Thermal expansion of CVD single crystal silicon was measured with a push-rod dilatometer up to 1100 °C for different crystallographic orientations of the specimen. Thermal analysis, Laue analysis and X-ray diffraction were used to verify silicon crystal orientation and absence of possible phase transformations. Coefficients of technical thermal expansion have been calculated in this temperature range and their variations with temperature have been demonstrated. These differences might cause anisotropy in thermal stresses, which has been calculated and compared with experimental values of dry-oxidised silicon wafers.     

Aging of steel deformed at low temperatures

Conclusions Plastic deformation at negative temperatures does not impair the ductile or plastic characteristics of aged steels 10G2Sl and 14KhGS; in some cases they are even improved.Central Scientific-Research institute of Ferrous Metallurgy. Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 11, pp. 48–50, November, 1969.     

Phase transformations in titanium alloys at low temperatures

Metal Science and Heat Treatment -     

1100铝合金轧制织构演变的定量分析

采用X射线衍射测量了1100铝合金不同变形量的冷轧织构,建立了织构体积分数和轧制真应变的数学关系式.结果表明在冷轧过程中,初始cube织构逐渐被转化成β纤维织构.随冷轧压下量的增加,cube,r-cube和剩余组分的体积分数减少,而β纤维组分的体积分数增加,织构体积分数随轧制真应变的变化可以用Avrami方程来描述.