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Hovanski, Yuri

Publications and source records attributed to Hovanski, Yuri.

17 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

Evaluation of intermetallic compound layer at aluminum/steel interface joined by friction stir scribe technology

Heat input and high strain rate deformation during friction stir welding of aluminum and steel resulted in the diffusion-based formation of a Fe x Al y intermetallic compound (IMC) layer. Compared with conventional friction stir welding tools, a friction stir scribe tool can reduce heat input significantly limiting the IMC layer thickness (~100–750 nm). Friction stir scribe joined lap joints fractured either through the welded interface or within the base aluminum alloy on the loading side, depending on IMC layer thickness during tensile lap shear testing. In addition, a modified effective heat of formation model predicted that Al 13 Fe 4 formed first at aluminum/steel interface and, during welding process, was substituted by Al 5 Fe 2 with local silicon enrichment, which was verified via microstructural characterization.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Friction stir welding bobbin tool

A bobbin tool is disclosed that includes a top shoulder, a bottom shoulder, and an axial pin that extends between the top and bottom shoulders. The bottom shoulder has an annular shoulder end surface, a back surface opposite the annular shoulder end surface, and a side surface that joins the annular shoulder end surface and the back surface. One or more and radially-extending blades may be disposed on the side surface of the bottom shoulder and/or one or more axially-extending blades may be disposed on the back surface. The one or more blades provide the bobbin tool with an ability to friction stir weld a variable thickness workpiece assembly, axially plunged through the workpiece assembly along an axis of rotation of the bobbin tool, and/or be extracted through the workpiece assembly along an axis of rotation of the bobbin tool.

47 OTHER INSTRUMENTATION↗
DOE OSTI2019

GALVANICALLY GRADED INTERFACE: A COMPUTATIONAL MODEL FOR MITIGATING GALVANIC CORROSION BETWEEN MAGNESIUM AND MILD STEEL

The impact of a graded metallic spacer on the galvanic corrosion between magnesium and mild steel is investigated in this work using a COMSOL model based on a validated numerical model. A graded spacer of 4 mm thickness decreases the peak galvanic corrosion by 50% over a system without a spacer, and 37% over a system with an aluminum spacer. The impact of the electrochemical properties of spacer materials is also investigated.

Spies, Kurt A.↗
DOE OSTI2018

System and process for friction consolidation fabrication of permanent magnets and other extrusion and non-extrusion structures

A die tool and process are described that provide friction consolidation fabrication and friction consolidation extrusion fabrication products including permanent magnets, and other extrusion and non-extrusion structures. The present invention overcomes previous particle size, texture, homogeneity and density limitations in conventional metallurgy processes.

42 ENGINEERING↗
DOE OSTI2018

Effect of hook characteristics on the fracture behaviour of dissimilar friction stir welded aluminium alloy and mild steel sheets

Under tensile shear loading, fracture modes of dissimilar lap welds produced by friction stir scribe technology were studied. Three fracture modes were observed. For zone A fracture, the initial crack was restrained, and the joint ultimately fractured in the base mild steel. For zone B fracture, the initial crack progressed through the aluminium sheet just above the Al/steel interface. For zone C fracture, the initial crack proceeded along the steel hook to the aluminium sheet surface. Fracture mode and joint strength were greatly influenced by steel hook size, and the steel hook size was affected by welding parameters and tool scribe height. In this study, the experimental joint strength achieved the calculated joint load limit.

Wang, Tianhao↗
DOE OSTI2017

High-Speed Friction Stir Welding of AA7075-T6 Sheet: Microstructure, Mechanical Properties, Micro-texture, and Thermal History

Friction-stir-welding (FSW) is a cost-effective and high quality joining process for aluminum alloys (especially heat-treatable allo ys) that has been applied successfully in the aerospace industry. However, the full potential of FSW on more cost-sensitive applications is still limited by the production rate, namely the welding speed of the process. The majority of literature evaluating FSW of aluminum alloys is based on welds made in the range of welding speeds around hundreds of millimeters per minute, and only a handful are at a moderate speed of 1 m/min. In this study we present a microstructural analysis of friction stir welded AA7075-T6 blanks with welding speeds up to 3 m/min. Textures, microstructures, mechanical properties, and weld quality are analyzed using TEM, EBSD, metallographic imaging, and Vickers hardness. Results are coupled with welding parameters to aid in the understanding of the complex material flow and texture gradients within the welds in an effort to optimize welding parameters for high speed processing.

Zhang, Jingyi↗
DOE OSTI2017

Friction stir scribe welding technique for dissimilar joining of aluminium and galvanised steel

Friction stir scribe technology, a derivative of friction stir welding, was applied for the dissimilar lap welding of an aluminum alloy and galvanized mild steel sheets. During the process, the rotating tool with a cobalt steel scribe first penetrated the top material — aluminum — and then the scribe cut the bottom material — steel. The steel was displaced into the upper material to produce a characteristic hook feature. Lap welds were shear tested, and their fracture paths were studied. Welding parameters affected the welding features including hook height, which turned out to be highly related to fracture position. Therefore, in this paper, the relationships among welding parameters, hook height, joint strength and fracture position are presented. In addition, influence of zinc coating on joint strength was also studied. Keywords: friction stir scribe technology; dissimilar material welding; zinc coating; hook height; joint strength; fracture position

Aluminum↗
DOE OSTI2017

Enabling Dissimilar Material Joining Using Friction Stir Scribe Technology

One challenge in adapting welding processes to dissimilar material joining is the diversity of melting temperatures of the different materials. Although the use of mechanical fasteners and adhesives have mostly paved the way for near-term implementation of dissimilar material systems, these processes only accentuate the need for low-cost welding processes capable of joining dissimilar material components regardless of alloy, properties, or melting temperature. Friction stir scribe technology was developed to overcome the challenges of joining dissimilar material components where melting temperatures vary greatly, and properties and/or chemistry are not compatible with more traditional welding processes. Although the friction stir scribe process is capable of joining dissimilar metals and metal/polymer systems, a more detailed evaluation of several aluminum/steel joints is presented herein to demonstrate the ability to both chemically and mechanically join dissimilar materials.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Solid-State Joining of Thick-Section Dissimilar Materials using a New Friction Stir Dovetailing (FSD) Process

Solid-state joining of thick section aluminum to steel plate has been achieved using a new process called Friction Stir Dovetailing (FSD). In FSD, a custom designed pin tool is used to flow a lower melting point material (AA6061) into dovetail grooves machined into the surface of an underlying higher melting point material (Rolled Homogeneous Armor – RHA). Repeating dovetails form a mechanical interlocking structure akin to metallic Velcro. In this study, AA6061 sections ranging in thickness from 1.5” to 3.0” are joined to 0.5” thick RHA plates. The effectiveness of FSD is demonstrated through tensile test data which shows specimens failing in the processed aluminum rather than at the joint interface. Numerical simulations are presented which highlight the importance of optimizing dovetail geometry. The effect of process parameters on joint strength, microstructure, and hardness are also discussed.

dissimilar metals joining↗
DOE OSTI2016

Joining Dissimilar Materials Using Friction Stir Scribe Technique

Development of a robust and cost-effective method of joining dissimilar materials could provide a critical pathway to enable widespread use of multi-material designs and components in mainstream industrial applications. The use of multi-material components such as steel-aluminum and aluminum-polymer would allow design engineers to optimize material utilization based on service requirements and could often lead to weight and cost reductions. However, producing an effective joint between materials with vastly different thermal, microstructural, and deformation responses is highly problematic using conventional joining and/or fastening methods. This is especially challenging in cost sensitive, high volume markets that largely rely on low cost joining solutions. Friction stir scribe technology was developed to meet the demands of joining materials with drastically different properties and melting regimes. The process enables joining of light metals like magnesium and aluminum to high temperature materials like steel and titanium. Viable joints between polymer composites and metal can also be made using this method. This paper will present the state of the art, progress made, and challenges associated with this innovative derivative of friction stir welding in reference to joining dissimilar metals and polymer/metal combinations.

Upadhyay, Piyush↗
DOE OSTI2016

JOINING DISSIMILAR MATERIALS USING FRICTION STIR SCRIBE TECHNIQUE

Development of robust and cost effective method of joining dissimilar materials can provide a critical pathway to enable widespread use of multi-material design and components in mainstream industrial applications. The use of multi-material components such as Steel-Aluminum, Aluminum-Polymer allows design engineers to optimize material utilization based on service requirements and often lead weight and cost reductions. However producing an effective joint between materials with vastly different thermal, microstructural and deformation response is highly problematic using conventional joining and /or fastening methods. This is especially challenging in cost sensitive high volume markets that largely rely on low–cost joining solutions. Friction Stir Scribe technology was developed to meet the demands of joining materials with drastically different properties and melting regimes. The process enables joining of light metals like Magnesium and Aluminum to high temperature materials like Steels and Titanium. Additionally viable joints between polymer composites and metal can also be made using this method. This paper will present state of the art, progress made and challenges associated with this innovative derivative of Friction Stir welding in reference to joining dissimilar metals and polymer/metal combinations.

Friction Stir Scribe↗
DOE OSTI2015

High-Speed Friction-Stir Welding To Enable Aluminum Tailor-Welded Blanks

Current joining technologies for automotive aluminum alloys are utilized in low-volume and niche applications, and have yet to be scaled for the high-volume vehicle market. This study targeted further weight reduction, part reduction, and cost savings by enabling tailor-welded blank technology for aluminum alloys at high-volumes. While friction stir welding has been traditionally applied at linear velocities less than one meter per minute, high volume production applications demand the process be extended to higher velocities more amenable to cost sensitive production environments. Unfortunately, weld parameters and performance developed and characterized at low to moderate welding velocities do not directly translate to high speed linear friction stir welding. Therefore, in order to facilitate production of high volume aluminum welded components, parameters were developed with a minimum welding velocity of three meters per minute. With an emphasis on weld quality, welded blanks were evaluated for post-weld formability utilizing a combination of numerical and experimental methods. Evaluation across scales was ultimately validated by stamping full-size production door inner panels made from dissimilar thickness aluminum tailor-welded blanks, which provided validation of the numerical and experimental analysis of laboratory scale tests.

aluminum↗
DOE OSTI2015

Friction Stir Welding and Processing

With nearly twenty years of international research and collaboration in friction stir welding (FSW) and processing industrial applications have spread into nearly every feasible market. Currently applications exist in aerospace, railway, automotive, personal computers, technology, marine, cutlery, construction, as well as several other markets. Implementation of FSW has demonstrated diverse opportunities ranging from enabling new materials to reducing the production costs of current welding technologies by enabling condensed packaging solutions for traditional fabrication and assembly. TMS has sponsored focused instruction and communication in this technology area for more than fifteen years, with leadership from the Shaping and Forming Committee, which organizes a biannual symposium each odd year at the annual meeting. A focused publication produced from each of these symposia now comprises eight volumes detailing the primary research and development activities in this area over the last two decades. The articles assembled herein focus on both recent developments and technology reviews of several key markets from international experts in this area.

friction stir welding↗
DOE OSTI2015

Thermal Microstructural Stability of AZ31 Magnesium after Severe Plastic Deformation

Both equal channel angular pressing and friction stir processing have the ability to refine the grain size of twin roll cast AZ31 magnesium and potentially improve its superplastic properties. This work used isochronal and isothermal heat treatments to investigate the microstructural stability of twin roll cast, equal channel angular pressed and friction stir processed AZ31 magnesium. For both heat treatment conditions, it was found that the twin roll casted and equal channel angular pressed materials were more stable than the friction stir processed material. Calculations of the grain growth kinetics showed that severe plastic deformation processing decreased the activation energy for grain boundary motion with the equal channel angular pressed material having the greatest Q value of the severely plastically deformed materials and that increasing the tool travel speed of the friction stir processed material improved microstructural stability. The Hollomon-Jaffe parameter was found to be an accurate means of identifying the annealing conditions that will result in substantial grain growth and loss of potential superplastic properties in the severely plastically deformed materials. In addition, Humphreys’s model of cellular microstructural stability accurately predicted the relative microstructural stability of the severely plastically deformed materials and with some modification, closely predicted the maximum grain size ratio achieved by the severely plastically deformed materials.

FSW↗
DOE OSTI2015

FSW of Aluminum Tailor Welded Blanks across Machine Platforms

Development and characterization of friction stir welded aluminum tailor welded blanks was successfully carried out on three separate machine platforms. Each was a commercially available, gantry style, multi-axis machine designed specifically for friction stir welding. Weld parameters were developed to support high volume production of dissimilar thickness aluminum tailor welded blanks at speeds of 3 m/min and greater. Parameters originally developed on an ultra-high stiffness servo driven machine where first transferred to a high stiffness servo-hydraulic friction stir welding machine, and subsequently transferred to a purpose built machine designed to accommodate thin sheet aluminum welding. The inherent beam stiffness, bearing compliance, and control system for each machine were distinctly unique, which posed specific challenges in transferring welding parameters across machine platforms. This work documents the challenges imposed by successfully transferring weld parameters from machine to machine, produced from different manufacturers and with unique control systems and interfaces.

aluminum↗
DOE OSTI2015

FRICTION STIR LAP WELDING OF ALUMINUM - POLYMER USING SCRIBE TECHNOLOGY

Friction Stir Scribe (FSS) technology is a relatively new variant of Friction Stir Welding (FSW) which enables lap joining of dissimilar material with very different melting points and different high temperature flow behaviors. The cutter scribe attached at the tip of FSW tool pin effectively cuts the high melting point material such that a mechanically interlocking feature is created between the dissimilar materials. The geometric shape of this interlocking feature determines the shear strength attained by the lap joint. This work presents first use of scribe technology in joining polymers to aluminum alloy. Details of the several runs of scribe welding performed in lap joining of ~3.175mm thick polymers including HDPE, filled and unfilled Nylon 66 to 2mm thick AA5182 are presented. The effect of scribe geometry and length on weld interlocking features is presented along with lap shear strength evaluations.

Upadhyay, Piyush↗