Conditions for growth of extended Al-rich Al-Mn alloy solid solutions and Al-Al6Mn eutectic during rapid solidification

Al-Mn alloys containing between 1.3 and 5.6 wt% Mn have been rapidly solidified by a modification of the Bridgman crystal growing technique at growth velocity V between 0.1 and 2 mm/s and a temperature gradient of 10 K/mm. Growth temperatures of the unextended and extended αAl solid solutions in the alloys respectively containing 1.3 and 2.1 wt% Mn, and of the extended Al-Al₆Mn eutectic containing 3.2 wt% Mn, have been measured as a function of V by interpreting the output of a sheathed thermocouple immersed in the melt and travelling with it during unidirectional solidification. These measurements of tip temperature as a function V for the Al-2.1 wt% Mn alloy are the first to be reported for a solid solution extended by rapid solidification. The measurements of tip temperature and concentration for both unextended and extended αAl solid solutions are in good agreement with predictions of a development by Kurz, Giovanola and Trivedi of Kurz and Fisher's model of dendritic growth. Corresponding measurements of growth temperature and eutectic spacing as a function of V for the extended Al-Al₆Mn eutectic containing 3.2 wt% Mn suggest that its growth is occurring at somewhat higher undercooling and larger spacing than predicted for growth at the extremum.