Metal Casting Technologies : MCT-2NDQRT-2017
FEATURE FEATURE 20 www.metals.rala.com.au METAL Casting Technologies 2nd Quarter 2017 21 Deformed weak pure metal sample (upper left) and strong new metal sample (upper right). Professor Xiaochun Li (lower left) and dispersed nanoparticles in magnesium matrix (lower right). “The results we have obtained so far are just a scratch on the surface when it comes to developing a new class of metals with revolutionary properties and functionalities,” says Professor Xiaochun Li, head of the research team. Li believes the development of a scalable manufacturing method could lead to a succession of high-performance lightweight metals and innovative applications. “We have been very busy in working on other lightweight metals too, such as aluminium and titanium,” says the professor. “We can now extend our reach to almost all metals, creating super metals that contain self-dispersed nanoparticles. We have also been working on 3D printing with such super metals.” Powdered progress When it comes to selecting metals for lightweighting applications, aluminium and its alloys are typically among the main contenders. Yet one of the less well-mentioned (and understood) aluminium options is aluminium powder metallurgy (PM). Aluminium (and other metal) powders are usually produced by gas atomisation. This process uses pressurised gas to disintegrate a stream of molten metal into fine particulates that are subsequently quenched (solidified) by a large volume of cooling gas. The powder then is rolled, extruded, squeezed or sprayed to create nearly finished components or blanks for further shaping. Powder metallurgy offers manufacturers a number of advantages over other metal processing techniques. z Net shape or near net shape components can be formed directly from the powder with minimal wastage. z Unlike casting, which typically involves a multi-step process to add strength, metal powder begins with a fine- grain, uniform microstructure, resulting in components with greater strength and lighter weight after single stage production process. z Powdered ceramics can be mixed with powdered metal in different ways to provide an even distribution of the ceramic particles, creating a composite with enhanced properties. z Powder allows for graded structures, with powders from two metals mixed together in different amounts for different sections of a component. This gives each section different performance characteristics. Last year Ames Laboratory (in Iowa) and Oak Ridge National Laboratory (in Tennessee) were awarded $5 million by the United States government to improve the production and composition of metal alloy powders used in additive manufacturing (AM). The use of metal alloys in AM has so far lagged behind that of plastics due to a lack of materials and process development. The ability to control the properties and quality of metal powders used in AM is critical to the quality of the final product, and the achievement of properties equal to conventionally cast and machined components. Innovative applications The use of metal powders and innovative metal powder processing techniques is already giving rise to a number of cutting edge materials. Researchers from Ohio-based Deep Springs Technology (DST) and the New York University Polytechnic School of Engineering have recently developed a magnesium alloy matrix composite reinforced with silicon carbide hollow particles. The matrix is created by combining hollow metal spheres with a metal powder that is then compressed until the pressure causes them to solidify. With a density of only 0.92 grams per cubic centimetre, this so-called composite “foam” actually floats on water, but is still strong enough to withstand the rigorous conditions faced in the marine environment. The silicon carbide particles also boost the impact protection qualities of the foam, with each shell acting as an energy absorber during its fracture. Researchers believe the new material could be suitable for both military and automotive applications, as it combines light weight with heat and impact resistance. Metal powders have also been used in the production of metallic microlattices. This new class of materials combines the useful mechanical properties of metals with smart geometrical orientations, providing even greater stiffness, strength-to-weight ratios and energy absorption capacities than other types of cellular materials such as foams. With the ongoing development of various manufacturing techniques such as AM, lattice materials with dimensions close to micrometre scale can now be produced. American airplane manufacturer Boeing recently revealed a microlattice which it claims is the world’s lightest metal structure, with potential applications in the aerospace industry. The end of heavy metal? Incredibly light. Super strong. Heat resistant. You only have to think of the demands on new metals and their applications to realise that lightweight innovation is happening all the time. Offering a compelling range of economic and environental benefits, today’s lightweighting revolution serves as a powerful demand driver for the casting, mining, alloy and advanced materials industries. Progressive foundries are well positioned to support this revolution, and to profit from it. By creating the components of a leaner, cleaner and more fuel-efficient economy, those engaged with the lightweighting drive can show how doing well for the environment can also be good for business. n Low Pressure die used for manufacturing an OEM’s cross member. Sarginsons believe they have created one of the world’s thinnest sandcast automotive components. THE ABILITY TO CONTROL THE PROPERTIES AND QUALITY OF METAL POWDERS USED IN AM IS CRITICAL TO THE QUALITY OF THE FINAL PRODUCT, AND THE ACHIEVEMENT OF PROPERTIES EQUAL TO CONVENTIONALLY CAST AND MACHINED COMPONENTS.