ighter, stronger aluminum components is the ultimate goal in a recently started research project that joins industry, research and academic institutions to develop innovative manufacturing solutions and transfer them into real-world production.  
In August, Lightweight Innovations for Tomorrow (LIFT) announced a new project intended to advance technologies for diecasting and heat treating aluminum parts, primarily for aerospace, defense and automotive applications.
“If we can reduce just a few ounces of metal from automobile engine mounting cradles or the housings that hold transmissions, we can deliver an impact that is multiplied by the millions,” said Larry Brown, executive director, LIFT. “In aerospace, an added benefit might lower manufacturing costs as well as increase fuel savings from the lighter weight designs.”
LIFT is operated by the American Lightweight Materials Manufacturing Innovation Institute and is one of the founding institutes in the National Network for Manufacturing Innovation, which is a federal initiative to create regional hubs to accelerate the development and adoption of cutting edge manufacturing technologies. It was formed in 2014, and the vacuum diecasting project is one of the first two started. The other project focuses on thin-walled gray iron parts.
Lead partners for the project are Boeing and The Ohio State University. The focus is to develop key process technologies (super vacuum diecasting and a shortened heat treatment) and computer engineering tools for 300 series aluminum diecasting alloys to improve mechanical properties and reduce the minimum wall thickness (up to 40%) and weight (up to 20%). According to Alan Luo, professor of materials science and engineering and integrated systems engineering, The Ohio State University, the project will reduce the variability in quality and improve the mechanical properties of high pressure die castings. The project also will explore new design methods of lightweight castings using local mechanical properties predicted by the new computer engineering tools, as opposed to the current casting design using minimum properties of cast alloys.
“If you can take a common part, such as an access panel you see on the wing of an airplane and use high integrity die castings, it could reduce weight and manufacturing costs,” said Russ Cochran, associate technical fellow, Boeing. “We hope to demonstrate that advances in high vacuum diecasting will produce parts that meet all the rigorous performance specifications we require, while realizing weight and efficiency goals.”
In current high-speed aluminum diecasting, microscopic air bubbles can form inside the part as the molten metal races through the mold. These tiny bubbles are not an issue for most diecast parts in typical applications, and engineers allow for them by using more metal and making parts thicker to meet strength and other performance requirements. These aluminum parts can achieve tensile strengths up to 47 ksi and minimum wall thicknesses of 0.04 in.
For this project, however, researchers are looking at methods to cast thinner walls with increased strength for structural applications, and for that, the bubbles can be detrimental. By applying a vacuum to the mold, diecasters remove air from the environment. Air is the culprit for porosity.
“We know in the laboratory that if we pull all the air out of the mold just before the molten metal flows in, we can eliminate the bubbles,” Luo said. “Without bubbles, we can design thinner parts that are just as strong and durable, but with less metal and lighter weight. There are other benefits, as well, because the new process allows us to heat treat parts after they are cast, which will improve their performance in service.”
The group also will be working on a shortened solution heat treatment to improve mechanical properties cost efficiently. A simple T5 heat treatment (where castings are cooled from an elevated temperature and artificially aged) has shown in preliminary work to increase yield strength by 40% for E380-type alloys. Now researchers want to see if a shortened T6 heat treatment (where castings are solution heat treated and artificially aged) can be developed to achieve even better properties in 300 series aluminum.
An important part of the two-year project will be enhancing the ability of computer models to predict the performance of aluminum diecast parts by combining information about the microstructure of the metal with a host of design and production parameters. The process, called integrated computational materials engineering (ICME), has great potential for reducing the time it takes to design and qualify new components for vehicles and will address some of the key challenges in implementing thin-wall diecasting technologies: die design, process control, casting design and process simulation.
Currently, castings are designed using the minimum properties of alloys as a baseline for the entire part. The ICME approach will allow designers to pinpoint higher or lower minimum properties to localized regions.
The aim is to connect the thermodynamic prediction of alloy composition and heat treatments to process modeling, which will enable designers to locate specific properties in specific areas of a part to meet service loading conditions. When load paths are clearly defined, the research group also plans on establishing topology optimization techniques to enhance design optimization.  
In the first three months of the project, the group has selected the baseline alloy (A380) and identified an experimental high strength aluminum alloy for structural casting development for aerospace and automotive applications. A concept design on a thin-wall casting die also has been started. The die is based on a thin-walled zinc die casting, which is being redesigned for aluminum. Researchers have begun mechanical property evaluation and ICME model validation in thin-wall casting development. Key real-world applications, such as an aerospace wing fuel door, to demonstrate the benefits of vacuum diecasting and ICME have been identified.  
“What we are doing here is bridging the gap between great research in laboratories and great manufacturing skills in private industry,” Brown said. “Once you bring these innovations into production, the results just multiply.”
Lightweight aluminum diecast components have a significant market to fill, particularly in the transportation industries, including aerospace, automotive, military and marine. Industry partners from these markets include Eaton Corp., Comau and Nemak. On the research side, Worcester Polytechnic Institute, Southwest Research Institute, the University of Michigan and Massachusetts Institute for Technology have joined the effort, while the American Foundry Society and North American Die Casting Association are assisting with modeling, technology oversight and dissemination of knowledge on how to manage the new thin-wall aluminum diecasting process in a production environment.
LIFT is operated by the American Lightweight Materials Manufacturing Institute and was selected through a competitive process led by the U.S. Department of Defense. It is one of the founding institutes in the National Network for Manufacturing Innovation, a federal initiative to create regional hubs to accelerate the development and adoption of cutting-edge manufacturing technologies.
After the two-year project is concluded, the group plans to deliver design guidelines and property specifications for thin-walled aluminum diecasting and ICME models for thin-wall casting design with location-specific properties. As these technologies and guidelines are incorporated into production diecasting operations, the options for aluminum components in structural applications will expand.   ■