Current Projects

Funded by ACRC Consortium

Green Alloy

Green Aluminum Alloy

Researchers: Shri Shankar, Diran Apelian

Focus Group Chair: Stuart Wiesner (Al Rheinfelden)

Sustainability is on the forefront of consideration in terms of materials production. Typically, when discussing recycling, most consider paper or plastics recycling but tend to neglect metal recycling. Aluminum alloys are unique in that sense as they are considered infinitely recyclable, provided they are properly sorted like plastics. The aluminum industry struggles to maintain scrap streams and often “downcycles” or mixes alloy streams resulting in the alloys losing their inherent value. Downcycling aluminum alloys predominantly takes place in the automotive industry. With the demand of structural alloys in the automotive industry there is immense pressure to develop pathways to upcycle the end-of-life automotive aluminum alloys.

The Green Alloy projects we have initiated at the ACRC investigates the inherent value of Twitch by conducting a robust chemistry and particle analysis of automotive aluminum scrap and develops the groundwork for upcycling Twitch without needing prior sortation. As part of the chemistry analysis of Twitch a dynamic (temporal and geographical) study of Twitch was conducted. This work resulted in a deeper understanding of the alloy diversity of Twitch and more importantly an average chemistry of molten Twitch that can be used as a starting point. Understanding the Twitch chemistry and the phases precipitating is paramount to applying efficient and viable metal processing technologies for refinement.

The project’s summit goal aims to utilize liquid metallurgical processing technologies to separate unwanted elements from the melt charge and create value from otherwise discarded material. The work goes over a detailed analysis of select processing technologies aimed at separating aluminum from the alloying/tramp elements found in Twitch. These scoping experiments show the viability of upcycling Twitch and their limitations for both refinement and industrial applicability. Overall, this work expands on refining an often downcycled scrap stream by utilizing select liquid metallurgical processing technologies and attaining upcycling in a cost effective manner.

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

Thermal Management During Solidification (ACRC)

Thermal Management of Permanent Molds

Research Team:

C. Ahn

C. Soderhjelm

D. Apelian

Thermal management plays a pivotal role in metal casting because it governs the solidification process, affects the resultant cast structure, and determines the operational cycle time. 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. Balancing these opposing thermal demands is particularly challenging in permanent mold casting, where complex geometries create non-uniform heat transfer conditions, leading overheating and overcooling.

The objective of this project is to advance thermal management methodologies for controlling heat transfer to maximize casting performance, (e.g. productivity and quality). The approach taken for this project lies in two major objectives listed below:

Evaluation of heat transfer characteristics for various thermal technologies
1. Purpose
  1. Quantify key heat transfer characteristics (heat flux, convective heat transfer coefficient, and interfacial heat transfer coefficient) across various thermal technologies under specific operational variables.
  2. Build a validated library of heat transfer boundary conditions for accurate mold temperature prediction in commercial casting simulations.
2. Approach
  1. Conduct heat transfer experiments based on operational parameters commonly used in casting industries.
  2. Finite element modeling and simulation to validate the experimentally measured heat transfer characteristics of thermal technologies via inverse methods.

Figure 1: Validation workflow (illustrated using direct-flame heating but applicable to all selected technologies). (Left) experimentally measured temperatures at multiple locations inside the steel die. (Right) corresponding finite element simulation results and error metrics used for validation.

Development of self-regulating permanent molds incorporating phase change materials (PCMs)
1. Purpose
  1. Demonstrate the feasibility and effectiveness of PCM-integrated permanent molds in improving thermal control and casting performance by leveraging the unique benefits of PCMs:
    1. Enable self-regulated thermal gradients (either steep or uniform) in molds through the exothermic and endothermic behavior of PCM’s reversible phase transitions during each casting cycle.
    2. Allow precise manipulation of mold thermal gradients based on the phase transition temperature of the selected PCM.
  2. Approach
    1. Develop design strategies for PCM-integrated permanent molds, focusing on geometric optimization.
    2. Quantify the interfacial heat transfer coefficient (IHTC) between the PCM and the mold to evaluate heat transfer efficiency during the casting process.
    3. Apply surface engineering techniques to further enhance heat transfer performance and efficiently control thermal gradients.

Figure 2: Schematic comparison of temperature gradients in a tool steel permanent mold and a phase change material (PCM)-integrated permanent mold during the (top) solidification and (bottom) preparation stages. The schematic highlights the critical moments of PCM’s phase transition – (top) solid to liquid during solidification, and (bottom) liquid to solid during the preparation stage.

Thermal Conductivity in Aluminum Alloys (ACRC)

Figure 1: Applications for ↑ conductivity & ↑ strength castable Al alloys

Pure Al is an excellent conductor with a thermal conductivity of ~237 Wm^-1K^-1 and an electrical conductivity of ~61% IACS (Annealed Copper = 100% IACS). However, currently existing castable structural aluminum alloys are limited to ~50% and ~70% of the conductivity of these values, respectively. Enhancing the conductivity of castable, structural Al alloys can improve efficiency and performance of electric vehicle powertrain components, heat exchangers, internal combustion engines, and other engineered products. Introduction of alloying elements into pure Al is necessary for castability and mechanical strength but inevitability reduces conductivity by introducing features that hinder electron and phonon transport:

Figure 2: The contradiction between strength vs. conductivity properties in metallic alloys

Traditional castable alloys rely upon eutectic alloy systems with high solid solubility in Al, a feature which is particularly detrimental to conductivity. A comprehensive review has been conducted to identify key, intertwined microstructural features that influence thermal and electrical conductivity in aluminum alloys, and propose viable pathways for achieving superior combination of conductivity, mechanical strength, and castability: https://doi.org/10.1016/j.msea.2024.147766.

This review identified low solubility eutectic systems — such as Al-Ni, Al-Fe-Ni, and Al-Ce — as promising alternative alloy systems deliver enhanced conductivity with decent mechanical strength and castability. This project investigates opportunities in these alloy systems in detail. Results from the first phase of this investigation are presented below:

Assessment of key microstructural features governing conductivity across Al-based eutectic systems (https://doi.org/10.1016/j.jallcom.2025.182055)
1. Purpose
  1. Conduct a comparative study across Al-based eutectic systems to determine which microstructural parameters at different length scales most strongly impact conductivity
2. Approach
  1. Cast 9 Al-based eutectic alloys targeting compositions with a 50% primary Al and 50% eutectic phase region (Al + eutectic phase) for comparison
  2. Simulate and measure electrical and thermal conductivity, correlating measurements with microstructural features across multiple length scales
3. Conclusions
  1. The key hierarchical microstructural parameters that dictate conductivity in order of dominance from greatest to least are 1) low solubility, 2) eutectic phase thickness and morphology, and 3) conductivity of constituent eutectic phases

Figure 3: Measured thermal conductivity across hypoeutectic alloys (W/m∙K).

Figure 4: High magnification secondary electron micrographs of deep etched a) Al-Mn, b) Al-Cu, c) Al-Si, d) Al-Ca, e) Al-Ce, f) Al-Co, g) Al-Fe, h) Al-Fe-Ni, and i) Al-Ni

Ultrasonic Processing of Al Alloys - Liquid Metallurgy (ACRC)

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 intermetallic phases. The conventional techniques used for these purposes require the extensive use of purge gases, rotating equipment, and chemical additions, each with their own challenges. Ultrasonic Treatment (UST) is a sustainable alternative to these traditional techniques where ultrasonic energy is applied into molten aluminum to modify the microstructure and cleanliness of the final casting. Through UST, degassing, grain refinement, and intermetallic morphology modification can all be accomplished with the sole addition of ultrasonic energy in one processing step. The objective of this ACRC project is to investigate the fundamental mechanisms of multifrequency UST applied in the liquid-state to overcome the current challenges in the field such as scalability, uniformity of treatment, and identifying appropriate parameters to increase the effectiveness of treatment for the targeted processing applications. This work dives deep into the solidification behavior and chronology that follow UST application of the melt to establish a mechanistic understanding of grain refinement and modification of intermetallics via UST. The alloys that are being investigated are: A380, A356, 7xxx wrought alloys, and Al-matrix nanocomposites.

Figure 1. (a) Schematic of the multifrequency UST setup in the 10 kg capacity induction furnace, (b) image of experimental setup.

The two impartment methods of UST are fixed frequency and multifrequency. In fixed frequency UST, a single frequency ultrasonic wave is imparted into the liquid longitudinally along the direction of the length of a solid probe. In multifrequency UST, there is one guiding wave in the ultrasonic frequency range (kHz) that is superimposed with multiple supporting waves in the megahertz range (MHz). These supporting waves will adjust their frequency as necessary to prevent decay of the guiding wave. This superimposition eliminates the nodes of non-treatment and gradients that exist in fixed frequency, to create a uniform field of cavitation bubbles and streaming loops. Multifrequency treatment uses a hollow probe where the ultrasonic waves are imparted perpendicular to the length of the probe to access a greater portion of the melt being treated.

The currently observed benefits of multifrequency UST treatment include the temperatures at which treatment is effective (over 100°C superheat), the volume of metal that can be treated (up to 20 kg compared to 1 kg in fixed frequency), the ability to spheroidize intermetallic phase morphologies, and significant grain refinement (up to 85% reduction in grain size), Figure 2. Multifrequency liquid-state UST proves to be a prominent route of exploration for industrial application.

Figure 2: EBSD patterns of as-cast A380 (top row) and A380 treated with 5 minutes of UST (bottom row) for temperature of (a) 660°C, (b) 680 °C, (c) 700 °C, and (d) 720 °C.

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)

Wire Arc Additive Manufacturing

Researchers: J.G. Webster, C. Soderhjelm, D. Apelian

The total aluminum content per vehicle is expected to increase significantly over the next decade due to electrification of the automotive industry. Presently, the most industrially deployed and cost-effective process to accommodate this demand for light alloy components is high pressure die casting (HPDC). Gigacasting is a recent process advancement building off HPDC that has allowed for the consolidation of multiple car parts into one large structural casting, improving manufacturing efficiency through the reduction in machining, post-processing assembly, and vehicle weight. The limiting factor in expansion of this technology is the tooling needed for continuous casting of larger components with varying thicknesses; localized control of heat is required to achieve uniform structural properties throughout the part without compromising cycle time or die life. Metal additive manufacturing (AM) is a pathway that can be exploited to generate complex tooling architecture that is otherwise not accessible with conventional subtractive fabrication systems.

Wire-arc additive manufacturing (WAAM) is a promising candidate to produce large-scale tooling integrated with novel thermal management technologies, such as conformal cooling and heating channels that contour the cast part. This route offers several advantages as compared to more conventional AM processes:

Increased deposition rate
Inexpensive feedstock
Higher energy efficiency
Larger build volume

Furthermore, the ability of WAAM to produce near-net shape components can improve material utilization and promote a single-line manufacturing system for the rapid production of casting dies. The process utilizes a welding heat source (GMAW, GTAW, or PAW) coupled with a robotic arm or CNC gantry to continuously deposit molten metal layer-by-layer into the desired geometry based on a 3D CAD file. A wide variety of welding wire alloys can be used as feedstock, which are inexpensive and require less consideration as compared to powders. Shielding gases are employed rather than a constrained build chamber to protect the weld pool from atmospheric contamination.

Due to the complex thermal cycles experienced by previously deposited layers during processing as well as rapid solidification rates inherent to WAAM, traditionally deployed tool steels are often printed with heterogeneous microstructures, high residual stresses, and defects that negatively impact the performance of the die. Unlike wrought steel blocks, there are currently no standards for post-processing treatments in AM to tailor the mechanical properties or address these issues. The current objective of this work through the ACRC is to leverage process improvements such as metal cored-wire feedstock additions for cold metal transfer (CMT) based WAAM and study the post-processing steps required to make these materials amenable to the tooling conditions of die casting.

Figures

Figure 1. Schematic diagram of a GMAW based Wire-Arc Addive Manufacturing system (Source: Xia, C. et al. A review on wire arc additive manufacturing: Monitoring, control and a framework of automated system. Journal of Manufacturing Systems 57, 31–45 (2020))

Figure 2. High speed camera footage of droplet detachment during cold metal transfer (CMT) welding, which is based off a modified GMAW process. (Source: www.fronius.com)

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