Microstructure and Mechanical Properties of Strip Cast Al-Mg-Si-X Alloys

Abstract

A study has been conducted on the microstructure and mechanical properties of strip cast Al6061 alloy with and without a 0.5 mass% Mn addition. The microstructures of the as-cast alloys are characterized by the presence of Si particles (<1 μm) and clusters of fine α-AlFeSi particles (<50 nm) along grain boundaries. In addition, there is the development of well-defined subgrains caused by the effects of hot rolling during strip casting. By T6 heat treatment, Si particles along grain boundaries are replaced by fine α-AlFeSi particles. There is also a formation of α-AlFeSi particles within the Al matrix by heat treatment. The addition of Mn results in an increase in the volume fraction of α-AlFe(Mn)Si particles within the Al matrix, which is associated with a corresponding decrease in the volume fraction of Mg₂Si precipitates within the Al matrix over that observed in the base alloy. Accordingly, the Mn containing alloy shows a lower yield strength but a higher ultimate tensile strength due to a greater work hardening rate than the base alloy. The increased work hardening rate of the Mn containing alloy is due to the presence of uniformly distributed fine α-AlFe(Mn)Si particles within the Al matrix. The present study shows that strip casting is a viable process for the fabrication of structural Al alloys.