Bob R. Powell

Microstructure and creep behavior in AE42 magnesium die-casting alloy

The micro structural analysis of die-cast AE42 reveals a correlation between micro structure and creep strength. A lamellar-phase Al11RE3, which dominates the interdendritic microstructure of the alloy, partly decomposes above 150‡C into Al2RE and Al (forming Mg17Al12). The increased solubility of aluminum in magnesium at higher temperatures may also promote the decomposition of Al11RE3. The creep strength decreases sharply with these phase changes. A mechanism for the decrease in creep strength of AE42 is proposed whereby the reduced presence of lamellar Al111RE3 and/or the presence of Mg17Al12 contribute to the observed poor creep strength at higher temperatures.

The electrochromic properties of sputtered nickel oxide films

Electrochromic nickel oxide films were prepared by reactive RF sputtering from a nickel target in an oxygen atmosphere. The films were deposited as a compact 40 nm layer of trivalent nickel oxide, Ni2O3. Reduction and oxidation of the films in 1 M KOH resulted in bleaching and coloration, respectively. Voltammetry indicated that the eventual electrochromic reaction involved the β-Ni(OH)2/β-NiOOH couple. In situ visible spectra showed electrochromic modulation of the transmittance throughout the visible range with a peak change in transmittance of about 60% at a wavelength of 500 nm. In situ spectra in the near-infrared region indicated improved electrochromic switching in this region; the sputtered nickel oxide film exhibited about a 30% change in transmittance in comparison to less than 10% for a similar electroprecipitated nickel hydroxide film. The sputtered nickel oxide films exhibited durable electrochromic switching for over 2500 coloration/bleaching cycles, a significant improvement over the less than 500 switching cycles exhibited by electroprecipitated nickel hydroxide films.

Magnesium Alloy Development for Automotive Applications

This paper summarizes the development of new cast and wrought magnesium alloys using computational thermodynamics tools and experimental approach. The Mg-Al-Ca alloys show excellent creep resistance due to the formation of high-temperature (Mg,Al)2Ca phase. The Mg-Al-Sn alloys are designed for mechanical properties and corrosion resistance through the optimization of Mg17Al12 and Mg2Sn phases in the microstructure. In the Mg-Zn-Ce system, Zn provides strength through solid solution strengthening while Ce increases the ductility via improved texture. Mg-Nd-Zn is a heat-treatable alloy system based on the precipitation hardening of Mg12Nd phase.

Encapsulation: A new mechanism of catalyst deactivation

Abstract Silica-supported platinum model catalysts show evidence of encapsulation when annealed at 1200 and 1375 K. The 100-nm Pt particles become partially immersed in the SiO 2 surface with concurrent formation of an SiO 2 ridge around the base of the Pt particles. A model of these processes has been developed which predicts this behavior based on the reduction of the surface free energy of the Pt SiO 2 system. Partial Pt encapsulation at lower temperatures and in more highly dispersed Pt catalysts is discussed and is shown to be a possible and as yet unreported mechanism of deactivation.

Analytical electron microscopy of a vehicle-aged automotive catalyst

Abstract Analytical electron microscopy techniques have been used to characterize fresh and vehicle-aged (51 680 km) samples of a commercial three-way catalyst containing Pt, Pd, and Rh. The average diameter of the particles in the aged catalyst was 9.6±2.0 nm (equivalent to 10% exposed metal atoms) while noble metal particles as small as 2.0 nm (48% exposed metal atoms) were observed in the fresh catalyst. Approximately half of the 10% exposed metal atoms in the aged catalyst did not chemisorb carbon monoxide and was presumably poisoned. Energy dispersive X-ray spectroscopic analysis showed that individual noble metal particles in both the fresh and aged catalysts contained more than one noble metal and, in one example from the aged catalyst, showed Pd and/or Rh surface enrichment in a Pt Pd Rh particle.

Automotive Mg Research and Development in North America

Expanding world economic prosperity and probable peaking of conventional petroleum production in the coming decades requires efforts to increase the efficiency of, and the development of alternatives to, petroleum-based fuels used in automotive transportation. North America has been aggressively pursuing both approaches for over ten years. Mainly as a result of lower prices due to global sourcing, magnesium has recently emerged as a serious candidate for lightweighting, and thus increasing the fuel efficiency of, automotive transportation. Automotive vehicles produced in North America currently use more Mg than vehicles produced elsewhere in the world, but the amounts per vehicle are very small in comparison to other materials such as steel, aluminum and plastics. The reasons, besides price, are primarily a less-developed state of technology for Mg in automotive transportation applications and lack of familiarity by the vehicle manufacturers with the material. This paper reviews some publicly-known, recent, present and future North American research and development activities in Mg for automotive applications.

The flexural strength and microhardness of YBa2Cu3O6+δ

The flexural strengths of rectangular YBa2Cu3O6+δ bars, prepared from mixed oxides and carbonates or spray-dried precursors, have been measured at room temperature and at 77 K. Strengths ranged from 17.8 to 57.6 M Pa at room temperature, depending on processing history, and were 20% greater when measured at 77 K. Corrosion of YBa2Cu3O6+δ in humid air at 38° C created two layers of corrosion products, but did not weaken the uncorroded core when failure loads were corrected for the decreased sample dimensions. The Knoop hardness of polycrystalline YBa2Cu3O6+δ ranged from 436 to 447 KHN while the hardness of individual grains of YBa2Cu3O6+δ was 498 KHN. Variations in flexural strength with microstructure were observed and are discussed.

The USAMP magnesium powertrain cast components project

Despite the demonstrated ability of magnesium alloys to significantly reduce weight at acceptable costs in many areas of an automobile, powertrain components have not benefited from this metal, primarily because the high-temperature alloys that are required for engines and transmissions are too expensive. However, the U.S. Department of Energy and the U.S. Automotive Materials Partnership have launched a project to evaluate several new, potentially low-cost magnesium alloys, design several pre-competitive power-train components for the best alloy properties, cast and dynamometer or vehicle test the components in assembled powertrains, develop a powertrain magnesium alloy design database and common alloy specification, and identify andpromote the funding of fundamental research into improved magnesium alloys and casting processes.

Progress toward a magnesium-intensive engine: The USAMP magnesium powertrain cast components project

The US Automotive Materials Partnership (USAMP) and the US Department of Energy launched the Magnesium Powertrain Cast Components Project in 2001 to determine the feasibility and desirability of producing a magnesium-intensive engine; a V6 engine with a magnesium block, bedplate, oil pan, and front cover. In 2003 the Project reached mid-point and accomplished a successful Decision Gate Review for entry into the second half (Phase II) of the Project. Three tasks, comprising Phase I were completed: (1) evaluation of the most promising low-cost, creep-resistant magnesium alloys, (2) design of the engine components using the properties of the optimized alloys and creation of cost model to assess the cost/benefit of the magnesium-intensive engine, and (3) identification and prioritization of scientific research areas deemed by the project team to be critical for the use of magnesium in powertrain applications. Phase II of the Project also comprises three goals: (4) casting and dynamometer-testing of the magnesium components in assembled powertrains, (5) developing a powertrain magnesium alloy design database and common alloy specification for magnesium powertrain alloys, and (6) promoting the strengthening of the scientific infrastructure for magnesium in North America to enable even more advanced powertrain applications in the future.

Magnesium alloys for lightweight powertrains and automotive structures

Abstract: This chapter introduces magnesium, the lightest of the structural automotive metals. it provides an overview of alloy nomenclature and properties, and the major casting, sheet forming, and extrusion processes. Descriptions of automotive magnesium applications produced by each process are provided and there is a summary that describes the challenges in alloy and process development that need to be overcome if the magnesium content in automotive sub-system applications is to be increased.