Materials Science Forum Vols. 618-619

Abstract: Friction stir processing (FSP) is a post-processing method that locally manipulates microstructure by imparting a high level of energy in the solid state giving rise to improved mechanical properties. FSP was applied to 25.4 mm thick, sand casting A206 aluminum workpiece under different parameters. Effects of FSP on microstructure evolution will be described and discussed. Specifically, through optical microscopy and SEM measurements the attained refinement in the stirred zone will be reviewed; porosity is significantly reduced and second phase particles are fragmented. Thermal conditions of the FSP zone have been measured as well as studying the effect of the temperature gradients on the resultant structure.

Abstract: The T5 heat treatment of semi-solid metal (SSM) processed alloy F357 was investigated by considering the effects of cooling rate and natural aging after casting, as well as artificial aging parameters on tensile properties. In addition, the tensile properties of SSM-HPDC F357 in different temper conditions (F, T4, T5 and T6) are compared. The Quality Index (QI) is used to compare the influence of different T5 heat treatment parameters and different temper conditions.

Abstract: In fabricating metal matrix composites, it is important to evaluate the coherence at the interface between the reinforcements and the matrix metal. Titanium particulates were selected as suitable reinforcements in this study because they had high hardness and Young’s modulus compared to the magnesium alloys used as the matrix, and also showed better ductility than those of ceramic particles. The wettability in the combination of pure magnesium and pure titanium was investigated in this study. The sessile drop method indicated that the contact angle in the case of Mg-Ti was 40°at 1073K in argon gas atmosphere, and showed an excellent wettability of pure titanium by molten pure magnesium. No intermetallic compound at the interface between them was detected. Titanium particulate could be effective reinforcements of magnesium composite materials. Water-atomized magnesium composite powders including titanium particles were used as raw materials, and consolidated by cold compaction and hot extrusion. When including about 3 mass% Ti particles, the magnesium composites reinforced with them showed significantly improved yield stress and tensile strength, while having good elongation.

Abstract: Cold spray coatings are considered promising for surface protection of Mg alloys from wear and corrosion since the process temperature is low enough to avoid oxidation of the Mg or any adverse affects on artificial ageing heat treatments. A special version of cold spray known as Kinetic Metallization has been used to produce pure Al and Al alloy metal matrix composite (MMC) coatings on AZ91 Mg alloy substrates in the present work. This surface treatment produces dense coatings with high adhesive and cohesive strength, which have substantially higher hardness and wear resistance than the AZ91 substrate material. The influence of coating composition and subsequent heat treatment on wear and corrosion performance have been investigated, using pin-on-disc wear tests, salt spray testing and electrochemical polarisation techniques. The heat treatment of the cold spray coatings is compatible with the solutionising and T6 ageing heat treatment of AZ91Mg. The results show that cold spray deposition of MMC coatings is a simple and effective technique for improving the surface properties of Mg alloys, both in the as-cast and in the heat treated condition

Abstract: Magnesium automotive components are currently produced by high pressure die casting. These castings cannot be heat-treated to improve the strength and ductility mainly due to the casting imperfections such as porosity and inclusions created by the air entrainment during the turbulent mold filing. These imperfections also prevent magnesium components to be used for highly stressed body components. Efforts were made to produce high integrity magnesium castings through a Super-Vacuum Die Casting process. The AZ91D castings were found to have very low porosity and can be heat-treated without blisters. The tensile properties of the castings were satisfactory. The mechanical properties and thermal analysis indicate that the conventional heat treatment procedure needs to be optimized for such thin sectioned and rapidly solidified castings which have very fine microstructures.

Abstract: As several of the free form fabrication processes progress with continuous process and material improvements, the feasibility of Rapid Manufacturing becomes more and more of a reality. Defined as the use of a Computer Aided Design (CAD) based automated additive manufacturing process to construct parts that are used directly as finished products and components, some of the rapid manufacturing processes are already competing with traditional processes such as injection moulding and progress is being made in applying the new technologies to the processing of metals, envisioning additive manufacture of high strength parts of unlimited complexity. While there have been quite a few successful attempts in the rapid production of complex medical implants using titanium alloys, 3D printing of sand moulds opens up yet another rapid manufacturing front, allowing for the rapid casting of aluminium and magnesium alloys. The effectiveness of such processes is yet to be researched in terms of process and product characteristics and the overall economy. This paper attempts to review some of the promising rapid manufacturing technologies for light metals processing and presents results of experimental investigations conducted to evaluate the effectiveness of the rapid casting process currently researched at the Rapid Product Development Centre of AUT University.

Abstract: The potential for Mg and Mg-Ni alloys to be used as hydrogen storage alloys has been known for some time. Although the maximum storage capacity in these alloys is high (7.6wt%H2 for Mg and 3.4wt%H2 for Mg2Ni), they have, until recently, been disregarded for practical applications due to their slow kinetics and high reaction temperatures. This paper discusses the recent discovery that the non-faceted/faceted hypo-eutectic Mg-Mg2Ni system can, similar to Al-Si eutectic alloys, be modified by trace additions and that this results in improved hydrogen storage properties. The hydrogen storage properties depend on the composition, including trace levels of modifying elements, and processing conditions. In alloys of optimal composition it has been shown that the reversible storage of 6.5-7wt% H2 is possible at a rate of reaction that is far better than that previously documented. In addition, the alloy can be satisfactorily processed in air, as opposed to controlled atmospheric conditions. This paper discusses the mechanism of improved hydrogen absorption/desorption kinetics when eutectic Mg-Ni hypo-eutectic alloys are modified. This discussion is based on atomic scale analysis using electron microscopy and examination with synchrotron radiation.

Abstract: The United States of America’s (USA’s) transportation system is strongly dependent on petroleum as an energy source. Petroleum is used to satisfy 95 percent of the USA’s transportation energy needs, consuming two-thirds of all the petroleum used in the USA. Since roughly 60 percent of the petroleum is imported, the implications of this dependency on energy security are readily apparent. Since 2002, the United States Department of Energy (USDOE) and the United States Council for Automotive Research (USCAR) have worked cooperatively through the FreedomCAR and Fuel Partnership (FC&FP) to fund high-risk, high-payoff research and development (R&D) into advanced automotive technologies with the potential for lowering this dependence. The FC&FP succeeded and built upon the Partnership for a New Generation of Vehicles (PNGV) initiative that ran from 1993 to 2001. The long-term transition of vehicles from gasoline to non-petroleum energy sources is viewed as critical in lowering the dependence of the USA economy on foreign oil, and in reducing the environmental impact of the personal transportation sector. The FC&FP supports research on technologies with the potential for energy-efficiency and renewable energy benefits, such as new engine concepts, lightweight materials, alternate non-petroleum based fuels, and hybrid propulsion components. This paper will highlight the research in the lightweight metals portion of the FC&FP. Cooperative R&D projects will be discussed which focus on processing and manufacturing technologies such as casting of magnesium (Mg) and aluminium (Al) alloy components, advanced forming techniques for Al sheet, and warm-forming of Mg sheet. The overall objective of these efforts is not only to demonstrate new technologies, but to reduce the cost of manufacturing lightweight materials and enable implementation of the technologies in high-volume automotive applications.

Abstract: Nano-structured metals have attracted growing research interest, which has brought about the development of methods for their fabrication. A number of fabrication methods involve severe plastic deformation, SPD, and involve refinement of the coarse-grained structures to grain sizes on a nanometre scale. Such grain refinement is accompanied by a significant improvement in mechanical strength. The improved properties of the nano-structured metals open up perspectives for their application in innovative industries such as aerospace, surface transport and biomedical implant manufacturing. The advantage of using nano-structured light metals is possible weight reduction of manufactured components. In the case of automotive parts, this may contribute to a reduction in CO2 emissions – one of the most important global challenges – due to the significantly higher strength of nano-structured metals and alloys compared to their microcrystalline counterparts. Nano-structured metals also exhibit high strain rate superplasticity at relatively low temperatures. This offers fast processing of materials, whose superplastic forming would be restricted otherwise. Finally, nano-structured metals also possess improved functional properties such as wear and corrosion resistance, which can broaden the range of applications of engineering metals and alloys even further. This paper reviews recent progress in the development of light nano-engineered metals and alloys. In particular, interest is concentrated on the metals and alloys processed by SPD methods. Conclusions are drawn with regard to future development of light materials for application in transport.

Abstract: Although mass reduction can be associated with additional costs, a decision to lightweight a structural subsystem may, depending on when in the vehicle development process the decision is taken, result in secondary (additional) mass savings such that the value of lightweighting is substantially increased. This paper overviews a method to estimate the potential for secondary mass savings in different vehicle subsystems. We close by describing current research efforts aimed at developing new lightweight product solutions for both body and powertrain applications along with commensurate manufacturing processes.