Current Projects

Funded by ACRC Consortium

Green Alloy

Green Aluminum Alloy

As the aluminum (Al) market continues to grow and the carbon footprint of the industry grows exponentially, we must implement novel technologies both in production and in recovery and reuse at the EOL. The International Energy Agency requires a 250 Mt CO₂e decrease from the Al industry under the Beyond 2 Degree Scenario which is a challenge for the industry. In 2021 the primary Al market produced 1,175 million tonnes of CO₂e. Secondary Al or Al made from scrap consumes 95% less energy than the primary production. However, maintaining quality scrap feedstock is challenging and can require extensive sortation and processing. The ACRC is developing sustainable high value Green Aluminum Alloys using low value post-consumer scrap (Twitch) and upcycling it without sortation of the Twitch. At the ACRC we are conducting a temporal and geographical analysis of the Twitch scrap stream to determine the overall elemental composition of Twitch feedstock allowing us to identify the major alloying constituents and tramp elements. We are applying liquid metallurgical technologies to process the Twitch (sans sortation) by targeting and removing unwanted phases, as well as adjusting the elemental composition to attain the targeted alloy composition. We are utilizing Integrated Computational Materials Engineering (ICME) to explore the alloy families that can be produced from molten Twitch for variety of engineered product applications.

Researchers: Shri Shankar, Diran Apelian

Focus Group Chair: Stuart Wiesner (Al Rheinfelden)

Twitch scrap or post-consumer automotive aluminum scrap is a difficult feedstock to properly recycle for a variety of reasons. The first being the variable nature of the scrap. It is an amalgamation of different cast and wrought alloys that when mixed and melted provide a low-quality alloy. Additionally, recycling a vehicle is not a surgical process and leads to multiple sources of contaminations leading to many tramp elements being place into the system. Currently the predominant pathway for Twitch is to be used for 380 alloys with dilution. To upcycle Twitch the first step is to understand the dynamic nature of its composition. Twitch varies temporally and geographically and understanding how it varies is crucial to knowing what the major constituents in your system are and what you need to do to handle them.

The next step is the purification of the molten metal. Since our project is focused on using Twitch without advanced sorting to remove specific pieces, the overall composition has multiple tramp elements. Molten metal processing technologies or “Liquid Metallurgy” allows us to target specific elements such as iron and remove them in the molten metal. This can be done with various techniques such as centrifugal refinement, filtration, or electromagnetic separation. These liquid metallurgical techniques will allow us to refine out the composition leading to a purer composition.

The final aspect of the project is to push the composition to structural capabilities. This means understanding where our composition is benchmarked and how it compares to traditional cast alloys. Utilizing ICME we can optimize and enhance the mechanical properties of our alloy allowing us to target specific properties for specific structural applications.

The Green Alloy project is dedicated to reducing the environmental impact of the aluminum industry while also utilizing our low value post-consumer scrap for upcycled purposes. This project also has the unique opportunity of taking one of the lowest quality scrap streams and showing the inherit value in it to help maximize it use.

Figure 1: Dynamic Composition of Major Elements in Twitch Scrap.

Figure 2: Image of various Twitch pieces.

Figure 3: Image of Twitch production.

Figure 4: Morphology of Twitch Composition

Development of an Al Based Structural Alloy Not Requiring Post-Solidification Heat Treatment (ACRC)

Overview

This project aims to develop a novel non-heat-treated Al alloy, having:

Good castability
A minimum yield strength of 120MPa (17.4ksi)
A minimum elongation of 11%.

An Integrated Computational Material Engineering (ICME) approach will be implemented to identify potential alloy compositions outside of the Al-Si eutectic that many die casting alloys are based on. Candidate alloys will be compared to A206 and A356 to identify eutectic systems with improved castability (hot tearing) while maintaining integrity of mechanical properties.

Researchers: B. E. MacDonald, C. Soderhjelm, D. Apelian

Focus Group Members

Chair – John Jiang (Harley-Davidson)

Kevin Anderson (Mercury Marine)

Stuart Wiesner (Al Rheinfelden)

Martijn Vos (Al Rheinfelden)

David Weiss (Eck Industries)

Category: Funded by ACRC Consortium

With the increased efforts in electrifying the transportation sector, the need for light weighting of vehicles with Al high pressure die cast components is growing. The heat treatment of die-cast components is both financially and energetically costly. Moreover, as the size of the casting increase the propensity for geometric distortion and surface blistering also increases. If successful, the developed alloy will enable the further implementation of high pressure die casting of large structural components in the transportation fleet of tomorrow.

Thermal Management During Solidification (ACRC)

Thermal management plays a pivotal role in the production of high-quality casting components and the reduction of production cycle time by ensuring desired solidification patterns during the casting process. Traditional batch processes, such as sand casting, have primarily relied on dissipating heat rapidly through designated locations using inserted chills. However, in dynamic casting processes like permanent mold casting and die casting demand not only rapid heat removal from the molten metal for solidification but also careful consideration of heat recovery for subsequent casting cycles. Particularly in the case of permanent mold casting, localized thermal management of molds becomes critical due to variations in required heat transfer caused by diverse mold geometries and shapes and challenges with accumulated thermal energy on the mold. The objective of this project is to develop thermal management methodologies for controlling heat transfer locally and dynamically to achieve high productivity with an acceptable quality of casting products.

Evaluation of heat transfer characteristics for various thermal technologies

Various novel technologies for heating as well as cooling are being investigated in this project. Both modeling and experimental paths are being taken to evaluate in a quantitative manner heat transfer characteristics: kinetics, heat flux, and heat transfer coefficients.

Development of self-regulating permanent molds incorporated with high-temperature phase change materials (PCMs)

Phase change material (PCM) is a substance that absorbs or releases sufficient heat energy during phase transformation to provide useful heating and/or cooling. The utilization of high-temperature PCMs within the molds can be advantageous for leveraging their latent heat properties during heating and cooling of casting processes. By incorporating PCMs, the permanent molds will gain self-regulating capabilities, which can serve as a foundation for the development of self-regulating molds. The ACRC project is evaluating PCM materials that are feasible and developing the operating guidelines to implement phase change materials in mold design and fabrication.

Thermal Conductivity in Aluminum Alloys (ACRC)

High Pressure Die Cast (HPDC) Al components constitute most electric vehicle powertrain components including electric motor housings, voltage inverters housings and heat sinks, and other vital units. However, the performance of these EV powertrains is often limited by thermal management issues. Developing higher thermal conductivity Al alloys can facilitate both superior performance and higher efficiency. Thus, the objective of this project is to investigate alternative Al eutectic systems to surpass the limitations of conventional Al-Si alloy systems.

Conductivity vs. Strength in Al alloys

Pure Al has a thermal conductivity of ~237 Wm^-1K^-1 and an electrical conductivity of ~61% IACS (Annealed Copper = 100% IACS). Although pure Al has by far the best conductivity properties relative to its alloys, alloying is necessary to achieve targeted mechanical properties. Ultimately, this alloy design endeavor becomes a balancing act as alloying elements introduced for strengthening purposes will inevitably result in adverse effects on thermal and electrical conductivity. Strengthening mechanisms including solid solution strengthening, precipitation strengthening, second phase strengthening, and grain refinement could be employed. An ideal Al alloy design requires reconciling these conflicting design criteria that inherently counteract each other.

Why Not Traditional Al-Si Alloy Systems?

Al-Si cast alloys account for 80~90% of the world’s castings. HPDC specifically accounts for more than ~60% of aluminum casting globally due to cost competitiveness for mass production. However, casting alloys such as 319, 360, and 380 alloys have low thermal conductivity of 109, 151, and 390 in the as-cast state. Although thermal and electrical conductivities can be enhanced through heat treatments, there is an inherent limitation in achieving high thermal and electrical conductivity Al alloys with decent mechanical strength within the Al-Si system. One of the most competitive Al-Si alloys in the market employs Sr modifiers to optimize the morphology of the Si phase to achieve ~90 MPa of yield strength and ~43% IACS in the as-cast state. However, alternative eutectic systems may offer mechanical and conductivity properties beyond what traditional Al-Si systems can offer.

Alloy Development Paths

The design investigations of alternative eutectic Al systems will follow two main paths: alloy design for optimizing as-cast conditions and alloy design for optimizing heat-treated conditions. Alloy design for optimizing as-cast condition will explore options that are more conducive to mass production due to the lack of heat treatments. Generally speaking, heat treatments enhance thermal conductivity of Al as alloying elements are removed from solid solution resulting in secondary phases. Therefore, the design objective of the heat-treatable alternative eutectic alloy system will be to maximize properties beyond what is commercially available, justifying the use of a heat treatment.

Ultrasonic Processing of Al Alloys - Liquid Metallurgy (ACRC)

Research Team: R. Fierro Jaime, D. Apelian

Focus Group Chair: Martijn Vos

Ultrasonic Treatment of Aluminum Alloys for Microstructural Modification

Traditionally, aluminum castings require various processing techniques such as degassing to reduce porosity, filtration to remove inclusions, the addition of grain refiners to refine the microstructure, and the addition of chemical modifiers to alter the morphology of phases. The conventional techniques used for these purposes require the extensive use of purge gases and chemical additions with adverse aftereffects. Ultrasonic Treatment (UST) is a ‘green’ processing technique through which ultrasonic energy is applied into molten aluminum to enact microstructural changes in the solidified cast. Through UST, degassing, grain refinement, and intermetallic morphology modification can all be accomplished with the sole addition of ultrasonic energy. The objective of this ACRC project is to investigate and compare various UST methodologies and establish the fundamentals of how ultrasonic energy can be absorbed, attenuated, and distributed throughout the molten metal to create microstructural change.

There are two prominent mechanisms of action created by UST within the molten metal which are acoustic cavitation and acoustic streaming. Acoustic cavitation is the formation and development of bubbles that compress and expand with time until an eventual collapse. Acoustic streaming is the formation of mass transport highways that encompass the entirety of the treatable volume. Together and at different treatment temperature ranges, these mechanisms can be taken advantage of to achieve a specified application. Current literature has investigated the applications of degassing, grain refinement, and intermetallic morphology modification within set temperature ranges. The ACRC research team aims to determine the fundamentals of UST at these different temperature ranges and establish the operation and coexistence of these two mechanisms for these applications. By changing the temperature range of treatment, the efficiency of UST via specific mechanisms can be determined.

Alongside this study of treatment temperature, the ACRC is also investigating the different methods of introducing ultrasonic energy into molten aluminum. UST equipment involves the use of an ultrasonic generator/power supply, a transducer which converts the power to an ultrasonic wave, and the probe which directly transmits the ultrasonic wave into the molten metal. The most common probe types allow for emission from the longitudinal direction for solid probes, and horizontally at 45⁰ increments for hollow probes. These different wave emission the ACRC to determine their effectiveness in regard to applications and treatment temperatures.

Figure 1: A visualization of the two prominent mechanisms of UST, acoustic cavitation (left) and acoustic streaming (right).

Figure 2: A temperature diagram establishing the UST applications and their treatment temperature ranges.

Diffusion Solidification (ACRC)

Research Team: S. Small, D. Apelian

Focus Group Chair: Paul Brancaleon, NADCA

Diffusion Solidification

Aluminum alloys are classified as cast and wrought alloys; the latter being difficult to cast as these alloys hot tear and thus need to be worked. Casting alloys on the other hand are castable in that their fluidity enables the molten metal to fill intricate shaped molds. Diffusion Solidification (SD) is a novel process that allows casting of wrought alloys directly into final shapes that are free of hot tears. The process follows a different route from conventional casting methods. In SD two liquid alloys of predetermined composition and temperature are mixed so that upon solidification the resultant alloy has a globular rather than a dendritic microstructure as shown below. The hot tearing tendency of wrought alloys originates from the inadequate permeability of their dendritic network, which obstructs the flow of interdendritic liquid and hinders compensation for shrinkage. The nondendritic microstructure made possible by SD minimizes hot tearing thus enabling wrought alloys to be cast directly.

Project Overview

Hot tearing, also known as hot cracking or solidification cracking, is a common casting defect that occurs during the solidification process of metals. Secondary dendrite arm coherency causes inadequate feeding of shrinkage by liquid metal in the solidifying regions and subsequent stress concentrations caused by shrinkage porosity. These stress concentrations initiate cracks under the high stresses associated with casting, severely decreasing mechanical properties, or even causing critical failure during solidification. Diffusion Solidification forms globular grains during solidification, eliminating the dendrite coherency point and allowing adequate feeding of shrinkage porosity to eliminate hot tearing and allow net shape casting of wrought aluminum alloys.

Diffusion Solidification achieves this by mixing two precursor alloys of distinct composition and temperature. Heat flow dominates solidification character in conventional casting of a homogenous melt, whereas Diffusion Solidification depends on liquid mixing and mass transport to define its solidification pathway. The unique solidification allows grains to grow in a globular morphology and eliminates hot tearing.

Funded by Federal Agencies

Rapid Creation of Tooling with Conformal Cooling (ATI)

Overview

Researchers: C. Soderhjelm, D. Apelian

Category: Funded by Federal Agencies

Increasing demand of aluminum die castings in structural and other applications are increasing due to their great performance to cost ratio. However, for the technology to stay relevant it has to keep up with the increasing demands, financial and technological, of the manufactured components. Superior properties and cycle times can be achieved by improving the thermal management during die casting of aluminum alloys. Heat extraction from the casting is key to achieve optimized castings at a higher cycle rate. Conformal cooling channels within the dies and its tools has the potential to create uniform and more efficient heat extraction. However, the complex geometries of that go hand in hand with conformal cooling channels are expensive and, in some cases, impossible to manufacture.

One of the great advantages of many additive manufacturing processes is the design freedom it offers. Building components from the bottom up, layer by layer, allows for the creation of complex shapes which would be impossible to make with traditional manufacturing methods. The flexibility of the additive manufacturing processes allows for possible reductions in both cost and lead times for tooling for the die casting industry.

A total of five die casting tools, such as cores and inserts, will be identified to be used for the qualification of additive manufacturing processes and materials. Successful results are considered when the lead time for manufacturing the tools is reduced from weeks to days and the tool life is comparable to the traditional H13 machined tools. From the work described below a set of guidelines for designing tooling with conformal cooling lines will be established.

DOD Mobile Foundry: Agile Production (SERDP)

Overview

Category: Funded by Federal Agencies

There is a need to improve the material sustainability of the warfighter. Currently, forward operating bases (FOB) produce an abundant amount of ferrous (iron) waste, which cannot be removed due to security reasons and local infrastructure constraints. However, an agile manufacturing process enables the reuse of scrap metal to produce needed parts for the warfighter.

Three manufacturing stages are addressed:

(1) quality control of the feedstock scrap material

(2) a stereolithography (SLA) enabled investment casting (IC) process, and

(3) post-process heat treating.

Cold Spray (ARL)

Category: Funded by Federal Agencies

Cold spray is promising technology for coatings, additive manufacturing, and repair of worn and corroded parts. Among its advantages are low temperatures, minimal oxidation, preservation of the powder feedstock’s microstructure, and a broad assortment of sprayable materials. However, the process is incredibly sensitive to the powder feedstock quality and it is not yet well understood how the composition and thickness of the powder’s passivation layer influences the critical velocity of powder particles. There is some indication that the formation of hydroxide and oxyhydroxide phases from absorbed water in the air contribute to a more ductile passivation layer which does not fracture during impact resulting in weaker deposits. Comprehensive studies of these effects in complex engineered alloys, such as widely used Al6061, will provide a foundation for improvements to powder storage and treatment to better combat adverse effects on the cold spray process.

Wire Arc Additive Mfg (WAAM) (ARL)

Overview

Category: Funded by Federal Agencies

Additive manufacturing has enjoyed explosive growth in recent decades thanks to the ability to reduce production times, reduce raw material consumption, and generate new geometries. Currently additive manufacturing with metals is largely dependent on powders which make the process slower, more expensive, and more hazardous than direct deposition based techniques, more commonly using for plastic additive manufacturing. This research aims to develop a new technique for metal additive manufacturing analogous to fused filament fabrication (FFF) for plastic printers. This is made possible by using semi-solid metals as the printing material. Semi-solid metals consist of an alloy which has both solid and liquid phases enabling the material to exhibit viscoelastic behavior so that it can be extruded through a nozzle into layers.

Reference:

Chen, L.Thornley, H. Coe, S. Tonneslan, E. Duoess, R. Hunt, M. Wight, D. Apelian, A. Pascall, J. Kuntz, C. Spadaccini, ”Direct Metal Writing: Controlling the Rheology through Microstructure”, Appl. Phys. Lett. 110, 094104 (2017)

The role of interstitial impurities in the design and processing of refractory complex concentrated alloys

Alloy Development & Process Control of Laser Powder Bed Fusion

Funded by Industry

Twinning During Czochralski Growth of Heavily Doped, Dislocation-Free Single Crystal Silicon (NASA)

Overview

Category: Funded by Federal Agencies

Advanced, low voltage power control electronics are needed to enable low power consumption computers, telecommunications and automotive devices. Lower voltage power electronics are made from dislocation-free silicon heavily doped with arsenic or antimony to provide extremely small electrical resistivity. As crystal resistivities have been lowered to attempt to achieve lower power losses, twinning of the crystal has unexpectedly occurred during growth, so that the crystal no longer possesses the required crystallographic orientation for device function. The purpose of this project is to determine the mechanism of twin formation, so that crystal growth process conditions can be designed to eliminate this defect and allow lower resistivity crystals to be grown reliably.

Knowledge Creation via Data Analytics in a High-Pressure Die-Casting Operation (Mercury Marine)

Numerical Modeling of Segregation and Shrinkage Porosity Formation in Multicomponent Al-alloys (Montupet)

Overview

Category: Funded by Industry