Brunel University's casting techniques could lead to lighter and recyclable car components

They aim to scale up research at Brunel University London’s Brunel Centre for Advanced Solidification Techniques (BCAST) and the Liquid Metal Engineering Centre led by Prof Zhongyun Fan.

He and his team have shown it is possible to condition molten aluminium alloys using melt shearing to produce castings with a much finer grain structure, so car components can be made up to 40 per cent lighter.

BCAST deputy director Dr Ian Stone told The Engineer: “One of the problems with liquid metals is that they contain oxide, so their surface oxidises and that oxide gets entrained within the liquid metal. It tends to act as a crack, so the industry spends a lot of time trying to remove oxide.”

“The high shear process applies very high shear forces to the liquid metal and that disperses those oxide films into very fine sub-micron particles,” he added.

“Partly by breaking that oxide up into very fine particles you make the oxide more benign, because it is not in a film form, and those oxide particles can act to enhance the nucleation of the grains as they solidify. By enhancing the nucleation you get more grains and therefore they must be finer.”

The team uses a high shear rotor stator device, which uses a rod with a small rotor on the end that sits within a fixed cylindrical stator.

“We spin the rotor at high speeds, let’s say 5,000rpm,” Stone said. “That sucks the liquid metal up into the device, and then applies the high shear between the rotor and the stator. It then pushes the liquid metal out through little holes in the walls of the stator, so you get recirculation of the liquid. That causes the oxide films to be dispersed into the small particles and when you solidify, those particles act as a nucleating agent. You are doing this to liquid metal, not during the solidification process.

“It means you can do a lot of recycling, because you are using that oxide rather than having to downcycle your material. It also allows us to remove iron, which is one of the major impurities when you recycle.”

Melt shearing is one of three methods being looked at by BCAST researchers to improve casting techniques, the others being grain refinement and ultrasound. Other work is aimed at making stronger and more ductile alloys.

Researchers will be able to test under industry conditions at Brunel’s new £17m research facility, the Advanced Metal Casting Centre, which was officially opened on 7 April, 2016.