Background

Cast aluminium alloys are widely used in light-weighting structures in the automotive and aerospace industry because of their high strength-to-weight ratios, anti-corrosion and good castability. However, the mechanical properties of commercially cast aluminium alloys are not as high as wrought aluminium alloys and other light‑weight materials, such as titanium-based alloys.

There is a need to improve existing alloys, developed several decades ago, as the mechanical property requirements have greatly increased since then. For industrial applications, particularly in automobile and aerospace, an increase in yield strength of 20% at room and high temperature (250°C) versus existing alloys, whilst maintaining ductility, would be a significant improvement.

Mechanical properties can be improved to some degree through micro‑structure refinement of both grains and secondary phases by chemical and physical methods. Another method of improving aluminium alloy strength is to add alloying elements to form nano-sized strengthening phases - precipitation strengthening. However there are limitations to how far this can be used due to the resultant reduction in ductility, measured as elongation. There is a need to increase tensile strength without sacrificing ductility.

In addition, existing cast aluminium alloys are relatively sensitive to the wall thickness of the castings. For example, for the commercial A356 alloy, the elongation can be reduced from 8% to 2% as the thickness of the castings is increased from 5 mm to 40 mm. There is a need to reduce such sensitivity to casting wall thickness.

Technology Overview

In order to obtain the desired benefits, existing commercial alloys are treated by adding chemical elements at a low level of up to 0.5% on top of that already in the existing commercial alloy. The elements that can be used are nickel, silver, niobium, molybdenum, cerium, lanthanum, yttrium, and scandium. They result in the formation of at least one type of sub-micron or nano-sized solid particles uniformly distributed in the solidified castings. The solid phases are formed as prior phases or as eutectic phases during solidification. They are controlled to exhibit a granular morphology with specified particle sizes and distribution which are too small to be detected.

Benefits

• Tensile strength increased by 20% at room temperature and high temperature (250°C) versus existing aluminium alloys;
• Ductility maintained at a same level as for existing aluminium alloys;
• Finer precipitates than that of the current commercial aluminium alloys so that particles are not detectable.
• The improved strength and ductility mean that existing parts can be re‑designed to be thinner than current parts, resulting in even greater weight saving than simply replacing steel with current aluminium alloys

Applications

• Automotive
• Aerospace
• Potential for replacing wrought aluminium alloys and titanium alloys

Opportunity

Brunel would like to hear from companies interested in joining a publicly funded consortium to further develop this technology.

There is also an opportunity to license the technology to manufacture the modified alloy and to produce cast aluminium parts.