THURSDAY AM
11:25 AM Super High Strength Aluminum Alloy Processed by Ball Milling and Hot Extrusion: Ruixiao Zheng1; Han Yang1; Zengjie Wang1; Shizhen Wen1; Tong Liu1; Chaoli Ma1; 1Key Laboratory of Aerospace Advanced Materials and Performance, Ministry of Education, School of Materials Science and Engineering, Beihang University Nanostructure strengthened aluminum alloy was prepared by powder metallurgic technology.The rapid solidification Al-Cu-Mg alloy powder was used in this study. To obtain nanostructure, the commercial powder was intensely milled under certain ball milling conditions.The milled powder was compacted first by cold isostatic pressing (CIP) at a compressive pressure of 300MPa, and then extruded at selected temperature for several times to obtain near full density material. Microstructure and mechanical properties of the extruded alloy were examined by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and mechanical tests. It is revealed that the compressive strength of extruded alloy is higher than 800MPa. The strengthening mechanism associated with the nanostructure is discussed. 11:45 AM Tailored Welding Technique for High Strength Al-Cu Alloy for Higher Mechanical Properties: Nagendrappa Biradar1; Ramling Raman1; 1 Indian Institute of Technology, Bombay AA2014 aluminum alloy, with 4.5% Cu as major alloying element, offers highest strength and hardness values in T6 temper and finds extensive use in aircraft primary structures. However, this alloy is difficult to weld by fusion welding because the dendritic structure formed can affect weld properties seriously. Among the welding processes, AC-GTAW technique is largely used for welding. As welded yield strength was in the range of 190-195 MPa, using conventional GTAW technique. Welding metallurgy of AA2014 was critically reviewed and factors responsible for lower properties were identified. Square-wave AC GTAW with Transverse mechanical arc oscillation (TMAO) was postulated to improve the weld strength. A systematic experimentation using 4 mm thick plates produced YS in the range of 230-240 MPa, has been achieved. Through characterization including optical and SEM/EDX was conducted to validate the metallurgical phenomena attributable to improvement in weld properties. Keywords: GTAW, square-wave-AC, transverse mechanical arc oscillation
TMP 8
Program Organizers: William Cassada, Alcoa Technical Center; Hasso Weiland, Alcoa Technical Center; Anthony Rollett, Carnegie Mellon University Symposium Organizers: Wojciech Misiolek, Lehigh University; Vivek Sample, Alcoa Inc. Thursday AM June 7, 2012
Room: McConomy Auditorium Location: University Student Center
Technical Program
Session Chair: Zenji Horita, Kyushu University
90
9:15 AM Development of Age-Hardening Technology for Ultrafine-Grained Al-Li-Cu Alloys Fabricated by High-Pressure Torsion: Hiroaki Motoshima1; Shoichi Hirosawa1; Seungwon Lee2; Zenji Horita2; Kenji Matsuda3; Daisuke Terada4; 1Yokohama National University; 2University of Kyushu; 3Toyama University; 4Kyoto University Recently, severe plastic deformation has attracted attention as a method for improving the strength of metallic materials. High pressure torsion (HPT) process is one of the most powerful techniques to fabricate ultrafine-grained materials. In this study, the development of high strength and high ductile materials was aimed by combination of severe plastic deformation and age-hardening techniques. The experiments were
conducted using 2091 Al-Li-Cu alloy sheet processed by HPT through Micro Vickers hardness test and TEM observation. Although the hardness of HPT-processed specimen monotonously decreases during aging at 463K, it was successfully achieved to increase the hardness up to 290HV by 373K aging. This result suggests that the combined processing of severe plastic deformation and age-hardening techniques enables the fabrication of ultrafine-grained alloys with highest strength among aluminum alloy wrought materials. 9:35 AM Evolution of Fragmented Fe-intermetallic Compounds in the SemiSolid State of Al-Mg-Si-Fe Alloys by Deformation Semi-Solid Forming Process: Chakkrist Phongphisutthinan1; Hiroyasu Tezuka1; Equo Kobayashi1; Tatsuo Sato1; 1Tokyo Institute of Technology Fe-intermetallic compounds are commonly considered as a harmful phase in the recycled aluminum alloys. The Deformation Semi-Solid Forming (D-SSF) process has advantages to modify these harmful compounds into more favorable particles by thermo-mechanical deformation and subsequently heating to the semi-solid state. The evolution of fragmented Fe-intermetallic compounds of the Al-Mg-Si-Fe alloy was investigated during heating to various semi-solid temperatures. The fragmented Feintermetallic compound was transformed into the polyhedral shape in the initial stage and subsequently spheroidized shape at the low semi-solid temperatures between 580-610oC. At temperatures higher than 613oC, fragmented Fe-intermetallic compounds completely melt into the liquid phase with long holding time. The Fe-intermetallic compounds are stable as solid phase at low semi-solid temperature and metastable at high semisolid temperature. 9:55 AM Break 10:25 AM Hierarchy-Strengthening in Al-Mg Alloys: Peter Liddicoat1; Maxim Murashkin2; Xiaozhou Liao1; Ruslan Valiev2; Simon Ringer1; 1The University of Sydney; 2Ufa State Aviation Technical University Utilising solute structures at multiple length scales, hierarchystrengthened Al alloys can exhibit yield strengths up to 1 GPa. Such internal alloy architectures are challenging to comprehensively characterise at the atom-scale – transmission-based microscopy (for e.g., TEM, XRD, or SAXS) may regularly encounter spectroscopic beam convolutions, from multiple nanocrystalline grains within a specimen, that can make information retrieval complex or impossible. Atom probe microscopy, a point-projection microscope, is not affected by grain size. Using novel techniques in atom probe to account for the complete activity of solute atoms, we will present the evolution of nanostructure at progressive strain increments imparted by high-pressure torsion in Al-Mg alloys. We will discuss defect-assisted solute clustering and the conceptual developments of chemical-texture and nanotopology to describe the intergranular relationships of misorientation and curvature to provide energetically favourable conditions for solute diffusion and partitioning. 10:45 AM Identification and Distribution of Fe Intermetallic Phases in AA5657 DC Cast Ingots: Zhan Zhang1; Gaofeng Li1; X.-G. Chen1; 1University of Quebec at Chicoutimi Iron intermetallic phases and their distribution in the direct chill (DC) cast ingots of AA5657 alloy have significant impact on the quality of final sheet products. However, identification and quantitative evaluation of ironbearing phases in the ingots are great challenge due to their small size and similar composition. In this study, the phase identification and quantitative evaluation were performed using combinations of electron backscattered diffraction (EBSD) and energy dispersive spectrum (EDS) on a scanning electron microscope, and image analysis techniques. The results show that there exist four iron-bearing phases (AlmFe, a-AlFeSi, Al3Fe, Al6Fe) in the AA5657 ingots. Using deep-etching technique, typical 3D