Improved Boralcan™ MMC Materials for Elevated Temperature Applications

Boralcan™ aluminum matrix composites using nuclear grade B4C have been used as neutronabsorbing materials for dry and wet storage applications for over 10 years. AA6351 has beensuccessfully supplied for extruded applications and has provided low density and good stiffness, adequate strength and compatibility with the extrusion process. However, improvements in strength, at elevated temperature, were required to more easily satisfy regulatory property requirements whilst still working within the AA6351 composition limits. Through careful optimization of the major alloying elements, Mg, Mn and Si, Rio Tinto Aluminium developed and commercialized 6351CO (“composition optimized”), which provides a 15% improvement in yield strength at 300°C. For designs not restricted to AA6351, further improvements in elevated-temperature strength have been achieved by the use of an Al-Mn-Mg AA3004 based material, which is compatible with both sheet and extrusion product forms.This paper describes the pilot and production scale development for these new materials conducted by Rio Tinto Aluminium. Mechanical properties at both room and elevated temperatures (25 to 300°C) are presented and rationalized in terms of the underlying metallurgical mechanisms.