In partnership with GKN Powder Metallurgy, Dalhousie University researchers are using neutron beams in studies aimed at opening up the automotive market to more products made from aluminum powders—a promising alternative to the heavier steel components used in the industry today.
Whether the goal is to save the environment by getting cars off fossil fuels or just to save money on gas by making vehicles more fuel efficient, experts agree that weight loss is the key.
That’s because lighter cars need less energy to run, regardless of the energy source. And since clean fuels do not pack as much punch as gasoline, reducing the amount of energy cars need to operate makes clean cars more feasible. In other words, the number of hybrid, electric, and fuel cell vehicles on the road is directly related to how much (or how little) cars weigh.
Not surprisingly, automobile manufacturers are increasingly looking for ways to use light aluminum materials in lieu of heavier metals like steel in many car parts. One technology that is helping this transition is known as ‘aluminum powder metallurgy.’ Here, aluminum-based powders are compacted in a die, and then heated under controlled conditions to convert the powders into solid material without melting it—a process called ‘sintering.’ Once the material is transformed into a solid, other traditional manufacturing processes can be applied to produce the final product. This technology offers cost savings by directly creating a part in the right shape, thereby reducing the need for subsequent modifications, such as machining, that are otherwise required to make components such as camshaft bearing caps, which secure the camshafts to the cylinder heads in vehicle engines.
One manufacturer that has been highly successful at producing camshaft bearing caps fabricated from aluminum powder metallurgy is GKN Powder Metallurgy, a company that is innovating to assist the automotive weight-loss trend.
“The use of lightweight materials, such as aluminum, and of powder metallurgy offer synergistic benefits to reduce weight,” says Alan Taylor, Vice President of Lightweight Technology at GKN.
Professor Paul Bishop of Dalhousie University in Halifax agrees, believing that aluminum powder metallurgy could be a vital key for weight loss—and subsequent energy savings—in the next generation of vehicles.
“There’s great potential for it to be used to make parts for a multitude of other automotive applications, as well as those within aircraft and military vehicles,” says Bishop. However, before this potential can be fully realized, “A key challenge is to increase fatigue strength,” he adds.
Fatigue strength refers to how well a material can withstand repeated changes in applied pressure or stress without fracturing. One way to increase fatigue strength is to apply a mechanical surface treatment known as ‘shot peening.’ Shot peening compresses the surface of the material, driving the atoms near the surface closer together than normal. This creates a condition known as ‘compressive stress,’ which makes the material more resistant to forces that try to pull it apart while it is in service.
To find out whether shot peening could be the answer to increasing fatigue strength in vehicle parts made from aluminum powder metallurgy technology, GKN teamed up with Bishop’s research group. ECKA Granules provided aluminum powders, which were compacted into bars at Dalhousie. The bars were then sintered in GKN’s industrial furnaces in preparation for shot peening and laboratory testing.
“The collaboration of GKN and Dalhousie has significantly pushed the technology to mainstream uses, with new high-strength powder metallurgy aluminum metal matrix composite applications in engines and transmissions,” says Taylor. “The current study with Dalhousie on shot peening has the potential to enhance mechanical properties further and to extend the applications of these materials.”
Early tests on the shot-peened aluminum powder metallurgy bars were very promising, showing more than a one-third increase in fatigue strength. To better understand this result, the researchers applied several different measurements techniques to compare the properties of the shot-peened bars to those without any surface treatment.
One of these measurement techniques involved using neutron beams at the Canadian Neutron Beam Centre (CNBC) to non-destructively measure the compressive stress based on how close together the atoms were at specific depths beneath the material’s surface. X‑ray measurements provided complementary measurements on the proximity of atoms very close to the surface.
Results showed that the compressive stress at the surface was four times higher in the shot-peened bars, and that this advantageous condition persisted to a depth of approximately 80 microns. As Bishop explains, “This is an exciting result because it’s very comparable to what is observed in shot-peened wrought aluminum alloys, which offer some of the best fatigue properties for light metals.”
Bishop and GKN are now applying other characterization methods to fully understand and optimize the shot-peening process for a number of aluminum powder metallurgy materials. The research team is particularly interested in how these materials behave in various thermal conditions, as the beneficial effect of shot peening doesn’t always last at higher temperatures. Hence, the researchers are currently gathering data on the thermal stability of these materials to help establish safe operational limits and thereby identify the full range of vehicle parts for which these materials would be suitable.
“While there’s still more development work to be done, it is likely that shot-peened components made from aluminum powders will evolve into commercial products,” says Bishop.
Undoubtedly, as more aluminum powder metallurgy parts are qualified for the automotive sector, vehicles will get lighter. Manufacturers will have more light alternatives for components traditionally made of steel and other heavy alloys. It will become more affordable to replace heavier components with lighter ones because parts made from aluminum powders are much less expensive than many of the aluminum products already in use in the automotive sector.
Not surprisingly, industry players are enthused by this research. “The collaboration of GKN and Dalhousie has significantly pushed the technology to mainstream uses, with new high-strength powder metallurgy aluminum metal matrix composite applications in engines and transmissions,” says Taylor. “The current study with Dalhousie on shot peening has the potential to enhance mechanical properties further and to extend the applications of these materials.”
The university researchers are grateful for the active participation by the industry. “Our success depends on a close working relationship with GKN every step of the way,” says Bishop, “Not only have they granted my team time access to their industrial production facilities, but they continually provide invaluable technical insight and actively review our progress.”