Entering the twilight zone of metals

CAST CRC scientist Dr Chris Gourlay has discovered that molten metals can behave like wet sand as they enter the twilight zone, an insight that could enable manufacturers to cheaply and efficiently produce better quality metal parts.

In the secret world of alloys, as molten metal cools it enters a twilight zone between solid and liquid where many problems that plague metal castings originate. Recent research shines new light on this mysterious state.

CAST CRC scientist Dr Chris Gourlay has discovered that molten metals can behave like wet sand as they enter the twilight zone, an insight that could enable manufacturers to cheaply and efficiently produce better quality metal parts.

The twilight zone for metal alloys as they cool from a liquid and start forming numerous solid crystals is also known as the “mushy zone” where alloys become a mixture of solidifying grains, surrounded by liquid – just like wet sand.

Most of us are familiar with wet sand drying up around our feet when we walk on the beach. This occurs because our weight forces sand grains apart, increasing the space between them. The liquid surrounding the grains is then drawn into these expanding spaces and the sand dries up around our feet.

In a breakthrough for metal technology, Dr Gourlay has found that, just like wet sand grains, metal crystals can be pushed apart under pressure causing alloys to expand as they deform.

According to Dr Gourlay, “when alloys enter the mushy zone they can behave quite unlike conventional solid or liquid metals, and behave more like soils in roadside embankments or partially molten magma in the earth”.

“This behaviour is especially important in metal manufacturing processes such as high pressure die-casting where alloys are formed into car parts whilst in the mushy zone. Understanding mushy zone deformation is central in controlling the flaws that form during manufacture.

“Now that we have an improved understanding of how metals deform as they solidify, we can begin to develop better manufacturing processes, which could increase productivity and reduce waste.”

Next time you’re driving a car, riding a bike or catching a bus give a thought to the mysterious twilight zone that the metals involved in your transportation have come through. Soon manufacturers may be able to control deformation in the twilight zone of liquid to solid, making metal components with fewer imperfections and better properties.

Dr Gourlay is one of the eight early career researchers selected to present their research findings Thursday (22 May) as part of a national conference of the Cooperative Research Centres Association (CRCA) in a session “Showcasing CRC Early Career Scientists” on 22 May 08 at 9.45 am at the Australian Technology Park.

For more information on the CRCA confrence please contact conference communication officer Michaela Lauren on 0417 260 603 or email media@crca.asn.au.