Researchers at ORNL, in partnership with FCA US and Nemak USA, have a new suite of aluminum-based alloys that could give automakers a boost in achieving ambitious fuel economy goals. (Earlier post.) The aluminum-copper-manganese-zirconium alloys—ACMZ—were developed in just under four years, lightning speed when it comes to developing a complex alloy.
Affordable, lightweight and capable of withstanding temperatures 100 degrees Celsius higher than commercially available automotive cast alloys, ACMZ is proving to be suitable for the next generation of more fuel-efficient internal combustion engines.
Current alloys inhibit engine efficiency because they soften at the peak temperatures present in highly efficient advanced engines. The aluminum alloys used today for cylinder heads—known as 319 and 356 grades—begin to severely weaken above 200 degrees Celsius (392 degrees Fahrenheit). Automakers need an alloy that can take the heat, is durable and can be used in existing manufacturing processes. ACMZ—which stays strong up to 300 degrees Celsius (572 degrees Fahrenheit)—meets all these parameters, FCA.
ACMZ, also known as 16HT, may enable engineers narrow the “bridge” areas in the cylinder head—the areas of metal between the valves, the spark plug and the direct fuel injector, FCA said. Narrowing the bridges frees up room for larger valves or even a second spark plug, giving engineers the flexibility to tailor an engine for the desired balance of performance and efficiency.
A cylinder head made of lightweight, high-temperature ACMZ, a new suite of aluminum-based alloys developed by researchers at ORNL. Image credit: Jason Richards, ORNL
A major difference between ACMZ and today’s automotive aluminum alloys is ACMZ’s use of copper, rather than silicon, as the strengthening component. Aluminum alloys with copper are not new, said Gregg Black, senior manager in Advanced Powertrain Engineering at FCA. However, they are expensive, produced in low volumes and haven’t been used in the auto industry due to a tendency for the part to develop small cracks during solidification after casting, an issue known as “hot tear.”
Oak Ridge’s advanced probes let engineers understand down to the atomic level what happens with an alloy as it cools, inspecting the formation, size and location of strengthening elements called precipitates.
The journey to ACMZ began in 2012, with a challenge from DOE’s Vehicle Technologies Office for a new high-performing alloy. A multidisciplinary team of materials, metallurgical and computational scientists led by ORNL’s Amit Shyam stepped forward and embarked on the development plan with help from industry partners FCA US and Nemak USA.
We knew this was going to be a steep goal to achieve in four years. To put it in perspective, it typically takes 10 to 20 years to develop a new material.—Allen Haynes, leader of the Materials Processing and Joining Group at ORNL
Shyam’s team first revisited history, comparing a group of industrially available aluminum alloys, including the RR350 alloy that evolved from a World War II aircraft application.
RR350 had remarkable high-temperature properties but had poor casting behavior and wasn’t affordable due to expensive nickel and cobalt additions, Shyam said. The team put RR350 under the microscope and imaged and chemically analyzed it to the atomic scale, enabling a better grasp of its properties.
We began to understand what happens to the structure and stability of the material as it goes through various temperatures and stresses and, in the process, discovered how to make it stronger and more castable while also eliminating expensive elements.—Amit Shyam
Using a predictive development process known as integrated computational material engineering (ICME), the Titan supercomputer enabled the team to virtually create 50 never-before proposed aluminum-copper recipes then simulate the cooling and performance properties. It helped the team narrow the field to seven high-potential alloys within 24 months.
The combination of our experimental research, computational calculations and materials characterization capabilities, along with regular participation from our two industry partners, helped us develop ACMZ. Early-stage research provided a fundamental breakthrough in metallurgy that was leveraged into the design of this new family of alloys.—Allen Haynes
Testing continues with FCA and Nemak to evaluate the alloy’s durability in engine applications. A cylinder head cast from ACMZ successfully completed FCA’s rigorous dynamometer test on a turbocharged engine in December 2017, and internal evaluations of ACMZ will continue throughout 2018.
FCA has been testing a current design cylinder head cast with the new ACMZ high-strength, high-temperature aluminum alloy.