Metal Casting Technologies : MCT-2NDQRT-2017
Despite the challenges, Sarginsons’ managing director sees a bright future for hollowed aluminuim and the techniques involved in its production. “We believe that low pressure casting is very much the future of lightweight vehicle chassis manufacture,” he says. “It allows the mass production of hollow castings in a way that high pressure casting is unable to.” Ramped up recycling Sarginsons is the official industrial partner of the recently opened $22 million Advanced Metal Casting Centre (AMCC), part of Brunel University’s Brunel Centre for Advanced Solidification Techniques (BCAST) in London. Headed up by Professor Zhongyun Fan, this state-of-the-art facility is designed to bridge the gap between fundamental research and full-scale industrial trials, with a focus on developing lightweight and completely recyclable automotive components. Fan and his research team have recently demonstrated that it is possible to condition molten aluminium alloys using melt shearing. By producing castings with a much finer grain structure, this technique can produce automotive components that are up to 40% lighter than their more conventional counterparts. “One of the problems with liquid metals is that their surface tends to oxidise,” explains BCAST Director of Programmes Eric Nyberg. “The oxide gets entrained within the liquid metal and frequently acts as a cracking agent. Industry therefore tends to spend a lot of time trying to remove it.” The BCAST team have spun liquid metals using a high shear rotor stator device, which uses a rod with a small rotor on the end that sits within a fixed cylindrical stator. “This process applies very high shear forces to the metal and that disperses oxide films into very fine sub-micron particles,” explains Nyberg. “By doing this you make the oxide more benign, with oxide particles enhancing the nucleation of the grains as they solidify, making them finer.” By allowing the integration of oxides, the new shear process removes the need to downcycle materials, leading to improved recyclability. It also allows the removal iron, one of the major impurities in recycled aluminium alloys. Closed loop collaboration BCAST’s shearing process is a continuation of the so-called ReALcar Project, which focuses on the development of a closed loop recycling process for aluminium. Started in 2008, the project was funded through innovation agency Innovate UK and industry partners including Jaguar Land Rover and aluminium producer Novelis. It has already led to the development of a new class of aluminium alloy (RC5754), made from recycled aluminium scrap, and innovative production systems which have integrated closed-loop aluminium into Jaguar Land Rover cars. “According to JLR, 75 percent of the aluminium 5754 used in their vehicles is the RC57574 recycled alloy,” says BCAST’s Nyberg. “We’re not that far away now from having a fully recyclable car.” Recycling is critical to both the economic and sustainable use of lightweight metal used in transportation applications. Between 1908 and 2007, 755 million tonnes of aluminium, 459 million tonnes of copper and 30 billion tonnes of steel were produced. It is estimated that more than half of this metal still exists as potentially recyclable stock. Professor Zhongyun Fan believes such metal stock could become an energy “bank” and a rich resource for meeting future metal needs. “Our aim is to lay down a solid foundation for full metal circulation, demonstrated initially with light metals,” explains Fan. “Such circulation would see global demand for metallic METAL Casting Technologies 2nd Quarter 2017 19 FEATURE 18 www.metals.rala.com.au FEATURE materials met by a full circulation of secondary metals, through reduced usage, reuse, remanufacture, closed-loop recycling and effective recovery and refining.” Nanoscale newness The search for strong, lightweight metals is seeing intensified interest in magnesium and innovative magnesium alloys. Magnesium, at just two-thirds the density of aluminum, is the lightest structural metal, and is already widely used in alloys that decrease the weight of parts used in vehicles, airplanes, power generation equipment, industrial processes and buildings. A research team at the Henry Samueli School of Engineering and Applied Science at the University of California, Los Angeles is now working on a super-strong yet light structural metal with extremely high stiffness-to-weight ratio. This new “super metal” is composed of magnesium infused with a dense and even dispersal of silicon carbide (an ultra-hard ceramic commonly used in industrial cutting blades) in nanoparticular form (less than 100 nanometres in diameter). It could be used to make lighter airplanes, spacecraft and cars, as well as in mobile electronics and biomedical devices. To create the new metal the UCLA team have developed a new way to disperse and stabilise nanoparticles in molten metals. Their technique of infusing a large number of silicon carbide nanoparticles gives magnesium added strength, stiffness, plasticity and durability under high temperatures. Ceramic particles have long been considered as a potential way of making metals stronger. But using microscale ceramic particles meant the infusion process resulted in a loss of plasticity. Nanoscale particles, by contrast, enhance strength while maintaining or even improving plasticity. Hand ladling of experimental aluminium alloy ingot. BCAST researchers confirming temperature during high shear, melt conditioned ingot casting. Molten aluminium flowing toward direct chill ingot casting system. BY ALLOWING THE INTEGRATION OF OXIDES, THE NEW SHEAR PROCESS REMOVES THE NEED TO DOWNCYCLE MATERIALS, LEADING TO IMPROVED RECYCLABILITY.