Effects of Cu and Mg on thixoformability and mechanical properties of aluminium alloy 2014

Thixoforming is a processing method that deforms metal in a semisolid state. The advantages of this process include the production of parts with good surface finish, fine microstructures and superior mechanical properties. However, the process mostly produces parts from aluminium cast grades, thereby not fully utilising the true potential of this method. Hence, thermodynamic modelling can be used to formulate alloy compositions that favour this processing method. Here, the effects of reducing copper content and increasing silicon and magnesium contents on the thixoformability of aluminium alloy 2014 were presented. The work consists of both the modelling and experimental validation. Results showed that by increasing Si and decreasing Cu content in the alloy, the solidification interval temperature was decreased and the temperature working window between the stipulated liquid fractions was widened, two of the characteristics favouring the process. A high solid-solution temperature employed resulted in the dissolution of unfavourable Mg2Si compound. An increase in Mg content used also resulted in the formation of the compact pi-Al8FeMg3Si6 phase and the decrease in the amount of the sharp and plate-like structure of the beta-Al5FeSi phase, improving the strength of the modified alloy. Subsequent T6 heat treatment successfully further increased the strength of the modified alloy.