Low-Cycle Fatigue of Ultra-Fine-Grained Cryomilled 5083 Aluminum Alloy

The cyclic deformation behavior of cryomilled (CM) AA5083 alloys was compared to that of conventional AA5083-H131. The materials studied were a 100 pct CM alloy with a Gaussian grain size average of 315 nm and an alloy created by mixing 85 pct CM powder with 15 pct unmilled powder before consolidation to fabricate a plate with a bimodal grain size distribution with peak averages at 240 nm and 1.8 μm. Although the ultra-fine-grain (UFG) alloys exhibited considerably higher tensile strengths than those of the conventional material, the results from plastic-strain-controlled low-cycle fatigue tests demonstrate that all three materials exhibit identical fatigue lives across a range of plastic strain amplitudes. The CM materials exhibited softening during the first cycle, similar to other alloys produced by conventional powder metallurgy, followed by continual hardening to saturation before failure. The results reported in this study show that fatigue deformation in the CM material is accompanied by slight grain growth, pinning of dislocations at the grain boundaries, and grain rotation to produce macroscopic slip bands that localize strain, creating a single dominant fatigue crack. In contrast, the conventional alloy exhibits a cell structure and more diffuse fatigue damage accumulation

Ultrafine grained plates of Al-Mg-Si alloy obtained by Incremental Equal Channel Angular Pressing : microstructure and mechanical properties

In this study, an Al-Mg-Si alloy was processed using via Incremental Equal Channel Angular Pressing (I-ECAP) in order to obtain homogenous, ultrafine grained plates with low anisotropy of the mechanical properties. This was the first attempt to process an Al-Mg-Si alloy using this technique. Samples in the form of 3 mm-thick square plates were subjected to I-ECAP with the 90˚ rotation around the axis normal to the surface of the plate between passes. Samples were investigated first in their initial state, then after a single pass of I-ECAP and finally after four such passes. Analyses of the microstructure and mechanical properties demonstrated that the I-ECAP method can be successfully applied in Al-Mg-Si alloys. The average grain size decreased from 15 - 19 µm in the initial state to below 1 µm after four I-ECAP passes. The fraction of high angle grain boundaries in the sample subjected to four I-ECAP passes lay within 53-57 % depending on the examined plane. The mechanism of grain refinement in Al-Mg-Si alloy was found to be distinctly different from that in pure aluminium with the grain rotation being more prominent than the grain subdivision, which was attributed to lower stacking fault energy and the reduced mobility of dislocations in the alloy. The ultimate tensile strength increased more than twice, whereas the yield strength - more than threefold. Additionally, the plates processed by I-ECAP exhibited low anisotropy of mechanical properties (in plane and across the thickness) in comparison to other SPD processing methods, which makes them attractive for further processing and applications

Trockenbohren und -Gewinden von hochlegierten Staehlen und Aluminiumgusslegierungen - Uebersicht sowie Stand und Probleme der Umsetzung in die Fertigung Schlussbericht

The report describes testing in drilling and taping of aluminium and high alloyed steel with minimal quantity lubrication. Progresses with optimized tools, machining problems, changes in the structure of steel and problems in mass production are shown. Examinations of the thermal behaviour explain the difference between dry-cutting and wet cutting. Also the influence of the wear of the tool is presented. Finally the modelling of the process dry-cutting with the method of finite elements is illustrated. (orig.)SIGLEAvailable from TIB Hannover: DtF QN1(66,40) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekBundesministerium fuer Bildung, Wissenschaft, Forschung und Technologie, Bonn (Germany)DEGerman

Effect of strain-rate on the deformation response of D0 3 -ordered Fe 3 Al

The mechanical response of centrifugally cast Fe(3)A1 with the composition Fe-27A1 (at.%) containing microalloying additions of Nb, Zr, C, and B was investigated over a wide range of strain rates between 10(-4) and 10(3) s(-1) at room temperature. Tests were carried out in compression using a (i) screw-driven load frame, (ii) drop impact tester, and (iii) split-Hopkinson pressure bar at quasi-static, intermediate and dynamic strain rates respectively. Post deformation analysis was carried out by DSC, SEM/EBSD, TEM and micropillar deformation. In all instances, the stress-strain curves show initial hardening (-first 5% plastic strain) followed by a plateau in stress. A loss in work-hardening occurs at the highest strain rates examined (>10(3) s(-1)) and is likely associated with shear localization; in addition, (2 11) [11 1]-type twinning was observed at these high strain rates at room temperature. This observation is in line with previous theoretical calculations of the antiphase boundary (APB) energy. The consequence of a continuously increasing yield stress with strain rate and a loss in work hardening at the highest strain rates together yields a maximum in flow stress at the intermediate strain rate. (c) 2015 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved