A calorimetric analysis of the response to heating of EN AW-2014 alloy formed in the liquid, solid and semi-solid states

A calorimetric analysis was undertaken to understand the phase evolution during DC cast, extruded and thixoforming of EN AW-2014 alloys. Extruded EN AW-2014 alloy responds to a heating cycle by the precipitation of the equilibrium θ-CuAl2 phase and its nonequilibrium precursors. This precipitation sequence is largely missing in the cast and thixoformed EN AW-2014 counterparts, suggesting that the precipitation capacity of these alloys is largely exhausted at very low temperatures. An additional endotherm is noted in the cast and thixoformed counterparts evidencing an additional soluble constituent, Cu2Mg8Si6Al5. Extruded EN AW-2014 alloy undergoes recrystallization between 500 °C and 550 °C while cast and thixoformed alloys undergo only grain growth. Cooling from solid-state forming is relatively faster and helps to retain much of Cu in solution offering a full precipitation sequence during a subsequent heating cycle ensuring substantial age hardening in the extruded alloy. A separate solution treatment is required to take advantage of the age hardening capacity of cast and thixoformed alloys.