Background

Magnesium alloys are lightweight (density 1.7 g/cc vs. 7.8g/cc for steel), easily recycled and durable so providing the best solution for reducing weight in the transport sector. Efforts to reduce fuel consumption and vehicle emissions in the automotive sector have increased the demand for lightweight magnesium alloys as structural materials, particularly Magnesium‑Aluminium alloys.

However increasing the use of these alloys to replace steel in the transport sector has been hampered by their lack of ductility and low yield strength. This is due to the large grain structure, large number of defects and large inter‑metallic particles formed during casting.

This results in parts with poor strength and very high scrap rates during casting.

Moreover it limits the design complexity of parts that can be cast with such alloys.

Technology Overview

Grain refiners are chemicals added at very low levels to a molten alloy in order to create a fine and homogeneous grain structure during solidification. They are commonly used in a wide range of metal alloys however no such suitable material exists for pure Magnesium, Magnesium alloys, and in particular for Magnesium‑Aluminium alloys.

Researchers at Brunel University London have developed an effective chemically stable phase at elevated temperatures where Magnesium-rich boride, Mg₁‑xAlxB₂, results in refinement of the grain size of the Magnesium‑Aluminium alloy.

The grain refiner has a good lattice match that can be uniformly dispersed within the magnesium-aluminium liquid prior to solidification (casting). These stable particles reduce the nucleation barrier, promote heterogeneous nuclei and increase the nucleation density in the melt. As a result, a fine grain structure with uniform distribution of the second phase and reduced micro-porosity (<0.01%) on a fine scale, is achieved.

The grain refiner can be added in powder form or as super concentrated master alloy that can be added at the foundry to the liquid metal prior to casting.

Benefits

• Improves tensile strength
• Improves ductility
• Improves homogeneity in mechanical properties across the component
• Improves castability of alloys by eliminating hot-tearing
• Enables thin-wall cast structures;
• Expected to reduce the high rejection rate during manufacture
• Easily incorporated into existing process and does not require new equipment at the found

Applications

The technology can be used to expand the use of Magnesium alloys in applications where previously they have failed due to their low ductility and strength in comparison with aluminium alloys or steel. The technology enables the wider use of light‑weight magnesium alloys which is of particular importance in the transport sector for reducing weight and so fuel consumption.

In addition there is a new opportunity to cast large and complex shaped structures using sand moulds that to date can not be done.

Opportunity

Brunel University are searching for collaborators to enable process scale‑up trials with a view to licensing the technology.