Materials Science Forum Vols. 539-543

Abstract: The structural control of A356 alloy, which was not studied among various electromagnetic processing of materials, was considered applying the alternating current and direct current magnetic flux density. The main aim of the present study is to investigate the effects of electromagnetic vibration on the macro and microstructure of A356 alloy in order to develop a new process of structural control in A356 alloy. When the electromagnetic vibration is conducted for changing the shape of primary aluminum, at low frequency (≤60Hz), the shape of dendrite is changed speroidal shape. When the electromagnetic vibration is conducted for changing the shape of eutectic silicon, a morphological change of the eutectic silicon from coarse platelet flakes to fine fiber shape is observed with EMV (Electro Magnetic Vibration) process at high frequency (≥500Hz).

Abstract: To restrain global warming, weight reduction of autobodies is needed for fuel saving and discharge of carbon dioxide (CO2) gas. Usage of light weight aluminum alloy sheets is efficiency for the weight reduction, but the less formabilities comparing with low carbon steel sheets restrict the usage of autobodies applications actually. To improve the formabilities of aluminum alloy sheets, asymmetric warm rolling is studied. The formability of a metallic sheet strongly depends on the textures. Lankford value (r-value), one of the indicators of formability, of recrystallized low carbon steel sheets is high because the density of {111}//ND orientation suitable for deep drawing is high. The texture of conventionally cold rolled and recrystallized aluminum alloy sheets mainly consists of cube texture which is lower r-value and unsuitable for deep drawing. It is well known that similar texture to low carbon steel sheet can be obtained by shear deformation in aluminum alloy sheets. To provide the shear texture in aluminum alloy sheet, asymmetric warm rolling is carried out at 473K-573K with differential roll velocities. A small amount of {111}//ND orientation which is hardly produced by conventionally cold rolling is observed in asymmetric warm rolled aluminum alloy sheets after recrystallizing. Controlling the asymmetric warm rolling conditions, such as rolling temperature, total reduction and asymmetric ratio, higher r-value and deep drawability comparing with conventionally processed aluminum alloy sheets are achieved. Other properties such as strength, elongation, and bendability of asymmetric warm rolled sheets are almost same as those of conventionally processed sheets.

Abstract: Computer based classification methodology is presented in the paper for defects being developed in the Al alloys as the car engine elements are made from them produced with the vacuum casting method. Identification of defects was carried out using data acquired from digital images obtained using the X-ray defect detection methods. The developed methodology as well as the related X-ray image analysis and quality control neural networks based software were carried out to solve this problem.

Abstract: Heat-treatable Al-Mg-Si aluminum alloys for automotive body panel applications are shipped and formed in T4 temper while still formable and are subsequently given a bake cycle to increase strength by age hardening while the paint is cured. However, the hardening response during the rather short industrial paint-bake is impaired upon natural ageing after the solution treatment. It is thus essential to counteract the adverse effect of natural ageing on bake hardening. While this is often accomplished by an additional ageing cycle before the paint-bake treatment, reversion treatments ought to be used once substantial natural ageing has first taken place to improve the bake hardening response of a twin-roll cast 6016 sheet. The present work was undertaken to improve the paint bake response of a twin-roll cast 6016 sheet by employing reversion treatments before the paint-bake cycle. Reversion treatments between 200°C and 250°C was effective in improving the bake hardening response of the twin-roll cast 6016 sheet which, when processed without reversion, failed to meet in-service strength requirements with a rather poor bake hardening response of 35 MPa.

Abstract: There has been an increasing tendency to determine liquid metal quality using pressure filtration methods such as Prefil Footprinter tests. The scientific understanding of this method, however, is emerging only recently with the introduction of derivative methods. Based on the investigation of flow behavior over the pressure filtration test, classic filtration theory has been successfully applied to understand the filtrate weight versus filtration time curve. The “clean” and “effective” resistance of filter medium, overall filtration resistance, cake resistance, pressure loss and distribution can be quantitatively calculated now. In the present work, a typical weight versus time curve from the Prefil Footprinter test of a cast Al-Si alloy is analyzed and discussed in details. The method developed in the work can provide new insights into the filtration behavior.

Abstract: A new superplastic Al-Mg-high Mn alloy called a high-Mn alloy in the present paper was developed. The superplastic properties of the high-Mn alloy were evaluated in comparison with a conventional superplastic 5083 alloy which was manufactured under the same industrial mass production process. The high-Mn alloy sheet of a middle thickness shows a lager elongation to failure at temperatures below 783K, and show better superplastic formability and less cavitation volume than the 5083 alloy. These superior characters of the high-Mn alloy may be ascribable to finer grain structure formed in the alloy.

Abstract: In-situ SEM/EBSP analysis has been performed during the evolution of the cube texture in a pure aluminum foil. In general, foils for capacitor are manufactured in an industrial process of casting, homogenizing, hot rolling, cold rolling (CR), partial annealing (PA), additional rolling (AR) and final annealing (FA). The foil samples after CR or AR in the process were analyzed by the SEM/EBSP technique at a constant temperature which was step-heated repeatedly by 10-20K from a room temperature to 623K or 598K. In a CRed sample, cube ({001}<100>) grains begin to grow preferentially at 503K to cover the sample. On the other hand, in a sample subjected to PA at 503K and AR, cube grains coarsened rapidly and preferentially at more than 533K in contrast to other oriented small grains remaining their sizes. Further, intragranular misorientation analysis revealed that the misorientation, which corresponds to dislocation density or strain, was much smaller in cube grains than in S ({123}<634>) and Cu ({112}<111>) ones.

Abstract: In this paper, the micro-damage mechanisms of 5A06 Al alloy weld joints have been studied under the condition of constant load and cyclic thermal load. The mechanical performance variation of the base material and its weld joint are analyzed and compared. Microstructure analysis reveals that the main damage mechanism in weld joints is the interior voids nucleation and growth. The voids distribution and evolution govern the damage process. Test results also show most fractures occur at HAZ near the welding fusion line. The development of these voids results in the performance deterioration of the weld joints under thermal cycling condition.

Abstract: The extrusion forces of the spray-formed Al-25wt%Si alloy at various strain rates and temperatures were calculated with the flow stresses obtained from high temperature compressive tests. The compressive stress-strain curves of the spray-formed Al-25wt%Si at various temperatures and strain rates were determined and discussed. The constitutive equation of strain rate as a function of stress and temperature described by, n Q RT A e ' / sinh( ) − ε& = ασ for the spray-formed Al-25wt%Si alloy, was established. The activation energy and constants in the constitutive equation were discussed and compared to other Al alloys. A direct extrusion experiment was employed to evaluate the extrusion loads vs. ram displacement at various temperatures and strain rates. By applying the constitutive equation, the extrusion loads were calculated and compared to the experimental ones for various temperatures and strain rates. The accuracy of the calculated results compared to the experimental results was discussed.

Abstract: The effect of Fe content on hot tearing of the high-strength Al-Mg-Si alloy was systematically investigated. In this study, a thermodynamic calculation software Thermo-Calc was used to calculate the solidification path under the non-equilibrium condition, and the mechanical properties of this alloy have also been investigated during solidification using an electromagnetic induction heating tensile machine. In order to confirm the calculation results of solidification path, a quenching test also was carried out. By using the Thermo-Calc, the sequence of crystallization, crystallization temperature of formed phases and their crystallized amount were systematically investigated for each alloy in which Fe content was changed. Furthermore, by comparing the fracture surfaces of the tensile testing sample and DC billet, the temperature range of crack initiation of the alloy was examined. Comparing the temperature range of crack initiation with the crystallization phase and its crystallization order, Fe content of high-strength Al-Mg-Si alloy influenced hot tearing significantly owing to the crystallization behavior of α(AlFeMn).