DETERMINATION OF THE THIXOCASTING TEMPERATURES OF AZ91D AND OTHER Mg ALLOYS USING A QUENCHING METHOD

Abstract The thixocasting injection temperature is a crucial processing parameter, frequently unavailable in the literature, especially for newly developed alloys. In this work, a simple and rapid method derived from the quenching method was developed to obtain an acceptable thixocasting injection temperature range for various magnesium alloys: AZ91D, AJ62x, AXJ530, MRI153 and ZAEX10440. Small specimens of each alloy were heated to appropriate temperatures within the semisolid range and quenched. Their microstructure was observed optically and the proportion of phase was measured using quantitative image analysis. The microsegregation was characterized and two different heating cycles prior to quenching were studied. The apparent volume fraction of the primary solid was determined as a function of quenching temperature between liquidus and solidus. These results were found useful to obtain a practical injection temperature range for each alloy and to obtain good quality thixocast parts. La température d’injection pour la thixocoulée est un paramètre crucial de procédé qui n’est pas toujours disponible dans la littérature et ce, surtout dans le cas de nouveaux alliages développés en laboratoire. Dans cet article, une méthode simple et rapide, dérivée de la méthode de trempe, est proposée pour estimer un intervalle de température d’injection d’alliages de magnésium tels que AZ91D, AJ62x, AXJ530, MRI153 et ZAEX10440. Des spécimens de chaque alliage ont été chauffés à différentes températures dans l’intervalle semisolide et trempés. Leur microstructure a été observée en microscopie optique et analysée quantitativement par analyse d’image afin de mesurer la proportion de la phase solide primaire. La microségrégation a également été mesurée dans les phases après trempe et deux cycles thermiques différents ont été comparés. La fraction volumique apparente de la phase solide primaire a été déterminée en fonction de la température de trempe entre le liquidus et le solidus. À partir de ces résultats, un intervalle de température a été estimé pour chaque alliage afin d’obtenir par thixocoulée des pièces d’excellente qualité.

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