- Email: [email protected]
PM aluminum at POWDERMET2015: Auto sees the light
Metal Powder Report Volume 70, Number 6 November/December 2015
metal-powder.net
SPECIAL FEATURE
PM aluminum at POWDERMET2015: Auto sees the light Joseph Capus The continuing popularity of the Ford F-150 pick-up has highlighted the consumer acceptance of lightweight aluminum in the automotive sector. PM aluminum developments are making further progress. PM light metals, aluminum, magnesium, titanium and their alloys were featured in a considerable number of sessions during the POWDERMET2015 conference in San Diego. Several of these presentations were given in a three-part Special Interest Program on Light Metals. Part 1 focused mainly on the end-user perspective beginning with a review of aerospace interests by David Saulnier (Boeing Research & Technology). Since about 35% of airline cost was fuel, weight-saving was a key element and was also important for certification. He went on to refer to developments in metal–matrix composites in airframe structures and the use of magnesium in gear-box housings. For additive manufacturing of aluminum components there was a need for proper specifications for materials, process control, QC and inspection. The energy perspective on light-weight PM applications was discussed by William Peter (Oak Ridge National Laboratory), dealing mostly with titanium PM and additive manufacturing, where the Department of Energy has funded much work and ORNL has 60 active projects. In Part 2, Ian Donaldson (GKN Sinter Metals) gave an overview of some of the trends in automotive light-weighting. He identified five ‘mega-trends’ that were seen by GKN as driving light-weighting: population growth, environmental issues, energy and resources, legislation and emerging technologies. Population growth implied a much larger middle class, especially in Asia, the development of infrastructure in mega-cities with more electric cars and autonomous vehicles, but more people working from home. On the environment there would be a large drive to achieve lower carbon emissions. On energy and resources, he saw more bio-fuels, fuel cells, as well as batteries for electric vehicles. Looking at the impact of these mega-trends on PM in automotive, for example in mega-cities there would be more restrictions E-mail address: [email protected]
on vehicles, so less single-person vehicles. On the other hand there would be opportunities for light-weighting in electric vehicles. Because of the weight of batteries, there would be increased need to offset this with lower density materials such as aluminum. He added that we are now seeing social pressures indicating more acceptance of the higher cost of light materials. That would also imply shifts in traditional manufacturing processes to produce components. Automotive light-weighting saw an annual growth rate just over 8% in 2014, major drivers being government regulations on fuel economy and emission controls. Another factor here would be globalization of government regulations. The Ford F-150 pick-up was a first-time example of consumer acceptance in a mass-produced vehicle, where switching to an aluminum body shed 700 lb in weight and showed a 10% gain in fuel economy. Donaldson also quoted an MIT study that showed every 10% reduction in vehicle weight resulted in a 6% increase in fuel economy for cars and 8% for trucks. This was a big driver. Significant weight reduction through light-weighting was expected in the next five years, largely in meeting fuel-efficiency requirements (increased CAFE standards). High-strength steel was still the best prospect from a cost perspective, but aluminum was now in second place. There would be more opportunities for aluminum as the limits to steel property improvements were reached. There had been about 10% improvement in the performance of light-weight materials in the past decade, which is closing the gap with steel. The main automotive opportunity for PM aluminum so far has been in camshaft bearing caps (Fig. 1), of which hundreds of millions have been produced. But this has been based on an alloy grade that is good for lowtemperature, low-stress applications where it has replaced cast iron. For further applications in transmission and engine components, improved mechanical properties are required: hardness, density, strength and wear resistance. Examples here would be 0026-0657/ß 2015 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.mprp.2015.08.021
294
FIGURE 1
PM alloy camshaft bearing caps: grand prize winner in the 2006 MPIF PM design competition, auto category (photo courtesy MPIF).
sprockets and rotors. Powder-forging of aluminum alloys was another area that could open up product opportunities by providing improved properties such as fatigue strength even higher than wrought. Powder-forged connecting rods could be an opportunity. Donaldson saw aluminum-based MMCs offering new potentials
SPECIAL FEATURE
for light-weighting. Overall, he saw lots of opportunities for lightweight PM products, and changes would be coming rapidly. Continuing in the same session, Donaldson stood in for colleague Logan Smith with a presentation discussing new PM aluminum alloy materials for automotive applications. As already mentioned, the driver is the heightened demand for aluminum to replace steel. However, currently available PM aluminum alloys are suitable for low-temperature, low-strength applications, but a lot of automotive applications are at some elevated temperature. There are new alloys in the 7000, 4000 and 2000 series but they generally show a significant drop in strength at 150 8C, particularly at longer times. In the search for elevated temperature resistance he compared the precipitation-hardening mechanism with dispersion-strengthening, the latter employing oxides, nitrides, carbides or intermetallics to achieve more thermal stability despite lower strength. Such metal–matrix composites (MMCs) have usually been made by the relatively expensive route of mechanical alloying followed by multiple processing steps, for example, extrusion, forging, rolling, etc. Donaldson said that in their work they chose a solid-state liquid-phase sintering (PM) route instead to get the
FIGURE 2
Tensile properties at room temperature and 150 8C for MMC PM aluminum alloys containing 2% and 5% aluminum nitride particles (after Smith, Donaldson and Hexemer). 295
SPECIAL FEATURE
Metal Powder Report Volume 70, Number 6 November/December 2015
SPECIAL FEATURE
SPECIAL FEATURE
lowest cost, namely, press, sinter and size. In order to explore this approach, test pieces made from commercially available powders were compacted to 2.5 g/cm3, sintered at 600 8C for 40 min followed by solutionizing and quenching, sizing, and finally artificial aging. Low melting point additives resulted in a high level of densification (>99%). Properties were checked for potential weight reduction in engine and transmission applications. Room and elevated temperature tensile and fatigue properties for Al–Cu–Mg–Sn matrix compositions with 2% and 5% aluminum nitride admixed particulate additions compared favorably with wrought 2014 aluminum alloy (Figs 2, 3). Green strength was also significantly improved by the presence of the aluminum nitride particles. The 2% and 5% AlN versions showed similar yield strength, tensile strength and elastic modulus at room temperature with a modest decline at 150 8C and less than for PM 2014 with no ceramic additives, indicating improved thermal stability provided by the ceramic particle content. The high-cycle fatigue tests showed superior fatigue performance at elevated temperature for the samples with the lower (2%) aluminum nitride content, while the 5% AlN samples showed a 15% drop at 150 8C compared
296
Metal Powder Report Volume 70, Number 6 November/December 2015
FIGURE 3
High-cycle fatigue properties at room temperature and 150 8C for MMC PM aluminum alloys containing 2% and 5% aluminum nitride particles (after Smith, Donaldson and Hexemer).
with room temperature. Fracture mode was reported to be unaffected by the presence of AlN particles. Donaldson added that these promising results were from early work and further investigation was needed.
metal-powder.net
SPECIAL FEATURE
PM aluminum at POWDERMET2015: Auto sees the light Joseph Capus The continuing popularity of the Ford F-150 pick-up has highlighted the consumer acceptance of lightweight aluminum in the automotive sector. PM aluminum developments are making further progress. PM light metals, aluminum, magnesium, titanium and their alloys were featured in a considerable number of sessions during the POWDERMET2015 conference in San Diego. Several of these presentations were given in a three-part Special Interest Program on Light Metals. Part 1 focused mainly on the end-user perspective beginning with a review of aerospace interests by David Saulnier (Boeing Research & Technology). Since about 35% of airline cost was fuel, weight-saving was a key element and was also important for certification. He went on to refer to developments in metal–matrix composites in airframe structures and the use of magnesium in gear-box housings. For additive manufacturing of aluminum components there was a need for proper specifications for materials, process control, QC and inspection. The energy perspective on light-weight PM applications was discussed by William Peter (Oak Ridge National Laboratory), dealing mostly with titanium PM and additive manufacturing, where the Department of Energy has funded much work and ORNL has 60 active projects. In Part 2, Ian Donaldson (GKN Sinter Metals) gave an overview of some of the trends in automotive light-weighting. He identified five ‘mega-trends’ that were seen by GKN as driving light-weighting: population growth, environmental issues, energy and resources, legislation and emerging technologies. Population growth implied a much larger middle class, especially in Asia, the development of infrastructure in mega-cities with more electric cars and autonomous vehicles, but more people working from home. On the environment there would be a large drive to achieve lower carbon emissions. On energy and resources, he saw more bio-fuels, fuel cells, as well as batteries for electric vehicles. Looking at the impact of these mega-trends on PM in automotive, for example in mega-cities there would be more restrictions E-mail address: [email protected]
on vehicles, so less single-person vehicles. On the other hand there would be opportunities for light-weighting in electric vehicles. Because of the weight of batteries, there would be increased need to offset this with lower density materials such as aluminum. He added that we are now seeing social pressures indicating more acceptance of the higher cost of light materials. That would also imply shifts in traditional manufacturing processes to produce components. Automotive light-weighting saw an annual growth rate just over 8% in 2014, major drivers being government regulations on fuel economy and emission controls. Another factor here would be globalization of government regulations. The Ford F-150 pick-up was a first-time example of consumer acceptance in a mass-produced vehicle, where switching to an aluminum body shed 700 lb in weight and showed a 10% gain in fuel economy. Donaldson also quoted an MIT study that showed every 10% reduction in vehicle weight resulted in a 6% increase in fuel economy for cars and 8% for trucks. This was a big driver. Significant weight reduction through light-weighting was expected in the next five years, largely in meeting fuel-efficiency requirements (increased CAFE standards). High-strength steel was still the best prospect from a cost perspective, but aluminum was now in second place. There would be more opportunities for aluminum as the limits to steel property improvements were reached. There had been about 10% improvement in the performance of light-weight materials in the past decade, which is closing the gap with steel. The main automotive opportunity for PM aluminum so far has been in camshaft bearing caps (Fig. 1), of which hundreds of millions have been produced. But this has been based on an alloy grade that is good for lowtemperature, low-stress applications where it has replaced cast iron. For further applications in transmission and engine components, improved mechanical properties are required: hardness, density, strength and wear resistance. Examples here would be 0026-0657/ß 2015 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.mprp.2015.08.021
294
FIGURE 1
PM alloy camshaft bearing caps: grand prize winner in the 2006 MPIF PM design competition, auto category (photo courtesy MPIF).
sprockets and rotors. Powder-forging of aluminum alloys was another area that could open up product opportunities by providing improved properties such as fatigue strength even higher than wrought. Powder-forged connecting rods could be an opportunity. Donaldson saw aluminum-based MMCs offering new potentials
SPECIAL FEATURE
for light-weighting. Overall, he saw lots of opportunities for lightweight PM products, and changes would be coming rapidly. Continuing in the same session, Donaldson stood in for colleague Logan Smith with a presentation discussing new PM aluminum alloy materials for automotive applications. As already mentioned, the driver is the heightened demand for aluminum to replace steel. However, currently available PM aluminum alloys are suitable for low-temperature, low-strength applications, but a lot of automotive applications are at some elevated temperature. There are new alloys in the 7000, 4000 and 2000 series but they generally show a significant drop in strength at 150 8C, particularly at longer times. In the search for elevated temperature resistance he compared the precipitation-hardening mechanism with dispersion-strengthening, the latter employing oxides, nitrides, carbides or intermetallics to achieve more thermal stability despite lower strength. Such metal–matrix composites (MMCs) have usually been made by the relatively expensive route of mechanical alloying followed by multiple processing steps, for example, extrusion, forging, rolling, etc. Donaldson said that in their work they chose a solid-state liquid-phase sintering (PM) route instead to get the
FIGURE 2
Tensile properties at room temperature and 150 8C for MMC PM aluminum alloys containing 2% and 5% aluminum nitride particles (after Smith, Donaldson and Hexemer). 295
SPECIAL FEATURE
Metal Powder Report Volume 70, Number 6 November/December 2015
SPECIAL FEATURE
SPECIAL FEATURE
lowest cost, namely, press, sinter and size. In order to explore this approach, test pieces made from commercially available powders were compacted to 2.5 g/cm3, sintered at 600 8C for 40 min followed by solutionizing and quenching, sizing, and finally artificial aging. Low melting point additives resulted in a high level of densification (>99%). Properties were checked for potential weight reduction in engine and transmission applications. Room and elevated temperature tensile and fatigue properties for Al–Cu–Mg–Sn matrix compositions with 2% and 5% aluminum nitride admixed particulate additions compared favorably with wrought 2014 aluminum alloy (Figs 2, 3). Green strength was also significantly improved by the presence of the aluminum nitride particles. The 2% and 5% AlN versions showed similar yield strength, tensile strength and elastic modulus at room temperature with a modest decline at 150 8C and less than for PM 2014 with no ceramic additives, indicating improved thermal stability provided by the ceramic particle content. The high-cycle fatigue tests showed superior fatigue performance at elevated temperature for the samples with the lower (2%) aluminum nitride content, while the 5% AlN samples showed a 15% drop at 150 8C compared
296
Metal Powder Report Volume 70, Number 6 November/December 2015
FIGURE 3
High-cycle fatigue properties at room temperature and 150 8C for MMC PM aluminum alloys containing 2% and 5% aluminum nitride particles (after Smith, Donaldson and Hexemer).
with room temperature. Fracture mode was reported to be unaffected by the presence of AlN particles. Donaldson added that these promising results were from early work and further investigation was needed.