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Products from Submicrocrystalline Aluminum Alloys

#2011


Development of Pilot Commercial Technology for Manufacturing of Products from Submicrocrystalline Aluminum Alloys with Enhanced Service Properties and Workability

Tech Area / Field

  • MAT-ALL/High Performance Metals and Alloys/Materials
  • MAT-SYN/Materials Synthesis and Processing/Materials

Status
8 Project completed

Registration date
11.10.2000

Completion date
20.07.2006

Senior Project Manager
Ryzhova T B

Leading Institute
Russian Academy of Sciences / Institute of Metals Superplasticity Problems, Russia, Bashkiria, Ufa

Supporting institutes

  • Makeyev Design Bureau of State Rocket Center, Russia, Chelyabinsk reg., Miass

Collaborators

  • University of Electro-Communications / Department of Mechanical Engineering and Intelligent Systems, Japan, Tokyo\nChungnam National University, Korea, Daejeon\nKorea Institute of Machinery&Materials, Korea, Changwon\nSendai Institute of Material Science and Technology, YKK Corporation, Japan, Miyagi

Project summary

The project is devoted to the development of basis of technology for manufacturing bulk aluminum alloys products with submicrocrystalline (SMC) structure (grain sizes less than one micron) by use of intense plastic straining (IPS) techniques. Applied research will be deal with examination of the effect of SMC structure on service properties and workability of aluminum alloys and optimization of thermomechanical treatment for processing SMC structure during IPS. Basic research will be carried out with threefold aims: to reveal mechanisms of SMC grain formation during IPS, to study origin of SMC structure effect on properties of aluminum alloys, and to examine mechanisms of recrystallization in intense strained materials. Use of technology developed will allow producing semi-finished products of aluminum alloys with enhanced service properties and workability. The new level of alloys properties obtained will expand a field of their commercial application and give advantages to producers.

Nowadays, the laboratory experiments have demonstrated that formation of SMC structure resulted in unique service properties and enhanced workability of a number of conventional alloys, aluminum based included. However, three main problems play a role of barriers for commercial implementation of this technology. First of all, the techniques used allow producing small sized laboratory samples only. It gives a limitation to evaluation of material properties and microstructures, as the commercial application of materials with SMC structure requires the examination of combination of mechanical properties according to standard procedure. This combination should include all main parameters of alloy strength in proposed service conditions. The lack of an information on mechanical behavior and structure stability of bulk SMC materials at elevated temperature has limited the use of aluminum alloys with SMC structure too. Secondly, scaling up the known laboratory techniques, such as equal channel angular extrusion (ECAE) and torsion straining under high pressure (TSHP), is essentially difficult and even impossible in a number of cases. And it is obvious that new techniques have to be developed for processing the metallic materials with SMC structure. Thirdly, microstructural evolution during IPS in aluminum alloys was poorly examined. It restricts feasibility for development of cost affordable technology for SMC aluminum products processing. As a result, the known methods of manufacturing of materials with SMC structure are rather expensive partly due to non-optimum route of thermomechanical treatment used.

The main goal of the project is to develop basis of commercial technology for manufacturing bulk products from aluminum alloys with SMC structure, evaluation of their service properties and workability. Two novel techniques involving IPS will be examined. The first one is complex angular extrusion (CAE) beings a unique processing technique, pioneered and patented at the Institute for Metals Superplasticity Problems. It could be realized in a specially designed die set to apply intensive plastic straining to bulk samples of different cross-sections. The second one is compression under high pressure (CHP). This technique was previously used for imparting fine grain structures (grain sizes in the range of one to ten microns) to aluminum alloys. In context of the project the CHP technique will be modified to produce SMC bulk billets. The patenting of this modified technology is planned under the frame of the project.

To develop cost affordable technology the following works will be carried out. Aluminum alloys will be deformed with ultra high strains by ECAE, CAE and CHP techniques. ECAE technique will be used in laboratory scale to study the evolution of microstructure during IPS. It will allow optimum regimes (temperature, strain, strain rate) of thermomechanical treatment to produce SMC structure in aluminum alloys to be developed. Regimes obtained will be used to process aluminum alloys by CAE and CHP techniques. Investigation of the effect of deformation scheme (path) on SMC structure formation will be performed. The combination of mechanical properties of CAE and CHP processed billets will be examined on samples of standard size. This combination include parameters of tensile strength, fatigue strength, hardness and toughness at ambient temperature, and superplasticity. Structure and service properties of heat treatable alloys will be studied in two states: before and after standard heat treatment. Evaluation the mechanical behavior of the alloys almost will include the analysis of their workability and the feasibility for cold rolling of thin sheets from aluminum alloys with SMC structure. These parameters are extremely important for beginning commercial use of developing technologies. The resulting microstructures and mechanical properties after CAE and CHP will be compared with those from other severe plastic deformation techniques.

As a result the present work will lead to new knowledge of the effects of phase composition, grain size and grain boundary structure on mechanical properties of aluminum alloys. The mechanisms of microstructural evolution during severe plastic deformation will be also examined. Besides, the work will advance the future commercial applications of SMC materials because of its focus on novel commercial aluminum alloys containing scandium.

Results of the work will allow evaluating feasibility of manufacturing of aluminum sheets with SMC structure and their use for low temperature superplastic forming of complex shaped products. Fulfillment of this project will allow promoting application of IPS techniques to commercial sized billets. The perspective areas of industrial application of aluminum alloys with SMC structure will be evaluated.

The State of the Art in the Field and the Impact of the Proposed Project on the Progress in the Field.

The proposed ISTC Project is a research and development work with high commercial potential for application in civil aircraft, automotive, railway and construction industry. This wok is related to the development of novel technologies for processing SMC structure in aluminum alloys and aimed on enhancement of service properties of these alloys and their workability.

Recently aluminum alloys with SMC structure have been produced with grain sizes less than one micron by IPS technique. These materials are of particular interest because of their unique physical and mechanical properties. For example, materials with SMC microstructures have been shown to exhibit significant increases in static strength at room temperature and superplastic behavior at low temperatures or high strain rates. The development of an SMC structure in relatively inexpensive commercial alloys produced by traditional casting technology is important for commercial implementation of this technology. The SMC materials could be used for the production of commercially important components with improved service properties using cold rolling, hot isothermal forging and superplastic forming. The aluminum industry is especially interested in the development and application of bulk SMC billets.

Several techniques, such as TSHP and ECAE, have been developed to subject materials to large plastic strains and thus develop SMC microstructure. These techniques have been applied to a several grade aluminum alloys with standard as well as non-standard compositions and positive result was demonstrated. However, the sample sizes produced and studied have been small. It restricts the use of these techniques in a laboratory scale. For commercial implementation of this technology, the process of severely straining materials must be scaled up to produce larger sample sizes. Bulk material properties must be established. The Institute for Metals Superplasticity Problems (IMSP) has developed novel techniques for intense plastic straining. These techniques allow producing massive billets with SMC structure, and its main advantageous is scale up feasibility. One of these techniques is CAE consisting in a combination of several deformation schemes in one deformation pass. Method and die design of CAE were covered by Russian Federation patent in 2000. Development and patenting of another technique being compression under high pressure (CHP) is in progress.

IMSP team has a great experience in examination of microstructural evolution during plastic deformation; evaluation of effect of deformation induced microstructure on service properties in numerous metallic materials including aluminum alloys. Examination of superplastic behavior is a main field of activity for most of IMSP’s researches. Researchers and engineers are perfect familiar with forging and rolling procedures and most of them are experienced with different IPS techniques during the last 10 years. All facilities requiring for proposed project are in good working conditions.

SRC team has a great experience (more than 30 years) in producing rocket parts from aluminum alloys, evaluation of service properties and microstructure of aluminum alloys. Weapon specialists are familiar with forging and rolling processing of light alloys. SRC has appropriate equipment to attend the goal of the present project.

Pioneer works of IMSP were dealt with examination of microstructural evolution during severe plastic deformation and evaluation of service properties in materials with SMC structure. In the same time, the mechanical behavior of SMC materials has been insufficiently examined. In many cases the evaluation of these properties has been limited by the small sample sizes produced by the ECAE and TSHP techniques. Particularly lacking are studies of fracture toughness and fatigue strength of SMC materials – two properties that are critically required for commercial implementation of these materials. In context of proposing project a number of important service parameters (including crack resistance, toughness and fatigue) will be evaluated in aluminum alloys with SMC structure as well as workability. The last is required for manufacturing of thin sheets by cold rolling and processing of parts by low temperature superplastic forming and forging. An effect of technological processing and final heat treatment on service properties will be evaluated. The mechanisms of grain formation and evolution of mechanical properties during severe plastic deformation are also poorly understood. An examination of the effect of IPS conditions on SMC structure formation is important for development of optimum route of thermomechanical treatment.

Knowledge of microstructure development during processing will permit efficient procedures to be implemented. It will allow essentially decreasing plastic strain evolved for SMC structure formation and result in a cost decrease.

Other poorly known aspect of materials with SMC structure is effect of following deformation and final treatment on its structure and properties. Analysis of microstructure evolution during fabrication and heat treatment is essential to understand microstructure changes that will yield final service properties. This is extremely important for cold rolling of thin sheets with SMC structure. Work outlined in this proposal will be focused on examination of microstructure evolution during both primary and secondary processing.

Project Purpose.

The general project objective is to develop the basis of commercial technology for manufacturing semi-finished products from aluminum alloys with SMC structure. In the frame of the project it is planned to analyze service properties and workability of these materials, examine the physical origin of grain formation during IPS and investigate an effect of SMC structure on aluminum alloy properties. The proposed project has six primary objectives.

1. Manufacturing bulk samples (at least 20 mm thick and weighing 0.5 kg) with uniform SMC structure using the CAE and CHP techniques.


2. Evaluation and analysis of IPS effect on microstructure evolution and the resulting properties.
3. Evaluation and analysis of post-deformation heat treatment effect on microstructure evolution and the resulting properties.
4. Evaluation and analysis of superplastic behavior of aluminum alloys with SMC structure.
5. Evaluation and analysis of the cold rolling of aluminum alloys with SMC structure.
6. Development of recommendation for commercial applications of the SMC alloys.

Two aluminum alloys developed in the former Soviet Union (1570 and 1421) and two US alloys (2219 and 6061M) will be studied in this project.

The 1570 alloy is an advance non-heat treatable alloy of Al-Mg system and can be used in aviation, railway and automotive industries, and other fields requiring a moderate strength and corrosion resistant aluminum alloys. The 1421 and 2219 alloys are heat treatable alloys and can be used in cryogenic applications as well. The 6061M alloy is a superplastic modification of 6061 aluminum alloy belonging to Al-Mg-Si system. The 6061 alloy is widely used in automotive, construction and aviation industries. It is presumable that the 6061M alloy will find an application in similar fields. The 1570 and 1421 alloys contain scandium, which produces fine dispersiods and is known to significantly influence mechanical properties and provide great thermal stability to the fine grain microstructure. These fine dispersoids should almost provide SMC structure stability in these alloys. Highly stable SMC structures are especially important for the heat treatable 1421 alloy, since fine grain microstructures need to be maintained during heating under quenching to attend high service properties. The 1421 and 2219 alloys contain large amount of reinforcement phases. From one side, such a composition hinders ability for cold rolling in 1421 alloy and, from another side, should provide high stability of SMC structure in these two alloys at a low temperature superplastic condition. The IMSP team has conducted preliminary examinations of these materials in small samples and found that SMC microstructures can be developed.

The Project realization will bring to reality the development of basis for commercial scale technology for manufacturing products (rods and sheets) from 1570, 1421, 2219 and 6061M aluminum alloys with SMC structure by CAE and CHP techniques. Service properties and workability of these alloys will be evaluated.

Following partial objectives will be attended in the context of the project:

– increase in ultimate strength and yield stress of aluminum alloys at room temperature at 1.2–2 times as much with sufficient resource of plasticity, fatigue resistance and toughness;


– optimization of technological route for manufacturing commercial sized billets from aluminum alloys with SMC structure;
– optimization of IPS methods, development design of tolling, manufacturing die sets;
– development of technological basis for manufacturing sheets suitable for low temperature superplastic blow forming from aluminum alloys with SMC structure;
– development of technology for low temperature blow forming of aluminum alloys with SMC structure;
– analysis of the effect of SMC structure on static strength, toughness and fatigue resistance of aluminum alloys;
– market evaluation for commercial use of aluminum alloys with SMC structure.

Applied research will be focused on service properties and workability of 1570, 1421, 2219 and 6061M alloys. The effect of heat treatment on evolution of SMC structure will be carried out. It can be expected that coherent nanoscale Al3Sc particles in the 1421 and 1570 alloys will stabilize SMC grains at heating up to a quenching temperature. Examination of microstructure evolution of aluminum alloys during IPS and following deformation and annealing as well as investigation of the effect of SMC structure on resulting mechanical properties will be carried out not only in the context of applied research but almost basic research. It will allow an outlook on the nature of deformation mechanisms and mechanisms of SMC grain formation, as grain boundary structure effects on mechanical behavior of aluminum alloys to be expanded.

Results obtained in this work could be used by aluminum industry for manufacturing bulk billets and sheets with SMC structure exhibiting enhanced service properties and improved workability from 1570, 1421, 6061M and 2219 aluminum alloys and alloys of the same series. SMC sheets and billets from these alloys can be suitable for low temperature superplastic forming and forging. Feasibility to produce sheets with improved service properties, especially from the 1421 alloy, will provide market by new products. A growth in market for these products can be expected.

Scope of activities.

The following activities will be performed in the context of the submitted Project:

1. Development of technical conception on tooling design for manufacturing commercial sized billets from the aluminum alloys by the use of CAE and CHP techniques. Development of design documentation and fabrication of tooling for CAE and CHP techniques. Evaluation of ability of these techniques to produce SMC structure in the 1570, 1421, 6061M and 2219 alloys in comparison with ECAE technique.

2. Development of technological route for producing SMC structure in the 1570, 1421, 6061M and 2219 alloys by CAE and CHP techniques. ECAE and small sized CHP (sample size does not exceed 20 mm×20 mm×80 mm) will be used to develop optimum route of thermomechanical treatment. Commercial sized billets will be produced by CAE and CHP techniques with the use of thermomechanical regimes based on ECAE and small sized CHP experiments.

3. Development of regimes for SMC sheets processing. A feasibility of cold (warm) rolling of billets with SMC structure produced by CAE and CHP techniques will be evaluated. Parameters of rolling will be developed for alloys of different nature. Basis for pilot technology of sheet manufacture of aluminum alloys with SMC structure (grain size in the range of 0.3–0.5 mm) will be developed. Pilot lot of thin sheets 150×300 mm in dimension will be produced.

4. Evaluation of room temperature service properties of aluminum alloys with SMC structure including static strength, hardness, plasticity, crack resistance, toughness and fatigue limit.

5. Examination of superplastic behavior of alloys with SMC structure. Low temperature and high strain rate superplasticity will be examined in tension and by biaxial test (blow forming test). Optimum regimes for blow forming will be developed. An effect of superplastic blow forming on resulting microstructure and properties at room temperature will be examined.

6. Examination the stability of SMC structure under post-deformation static annealing of IPS aluminum alloys. Evaluation of an effect of conventional heat treatment on structure and resulting properties of the 1421 aluminum alloy with initial SMC structure will be carried out.

While implementing the Project the following activities will be pursued:


– The tooling design will be performed for CAE and CHP techniques to manufacture commercial sized billets from the aluminum alloys with SMC structure (technology development).

– Feasibility for SMC sheet processing by cold (warm) rolling will be examined for billets produced by CAE and CHP techniques (technology development).

– Superplastic parameters will be determined for alloys with SMC structure at tension and biaxial (blow forming) tests (applied research). The origin of low temperature superplasticity in aluminum alloys with SMC structure will be examined (basic research). Optimum regimes for low temperature blow forming will be developed for alloys with SMC structure (technology development).

– An origin of SMC structure formation during IPS will be examined (basic research). On this basis the optimum regimes of thermomechanical treatment will be developed to produce uniform SMC structure in bulk billets (technology development).

– Phenomenology and nature of effects of IPS and SMC structure on mechanical properties of aluminum alloys will be analyzed (applied and basic research).

– Phenomenology and origin of evolution of SMC structure and mechanical properties during post-deformation annealing will be examined (applied and basic research). Feasibility to use structure hardening effect caused by SMC structure formation will be evaluated in a heat treatable aluminum alloys to enhance service properties (applied research and technology development).

– Preparation of annual and final reports and a technology implementation plan for a commercial use of technology developed.

Role of foreign collaborator.

Prof. Taku Sakai is a worldwide known expert in the field of grain boundary formation and grain refinement during plastic deformation of metallic materials, aluminum alloys included. His recent activities are focused on IPS and analysis of the effect of fine grain structure on mechanical properties of metals and alloys. He and his group will take part in technical monitoring of the project activities. The team will take part in discussions of current project tasks, joint publications and patents. Prof. Taku Sakai will focus his efforts on the forecasting of commercial profits from the use of technology and equipment developed for producing SMC structure in aluminum alloys. He will evaluate market in Japan, USA and EC for this technology. Coupling of foreign collaborator and Russian institutions efforts for project fulfillment will assist in acceleration of commercial implementation of the technology developed for manufacturing aluminum alloys with SMC structure and enhanced service properties and workability.


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