Experimental study of the solidification of Sn-10 wt.%Pb alloy under different forced convection in benchmark experiment
Résumé
A solidification benchmark experiment was designed and developed at SIMAP Laboratory in Grenoble in order to investigate the structure formation as well as solute macro-mesosegregation by means of a well-controlled solidification experiment. The experiment consists in solidifying a rectangular ingot of Sn-10 wt.%Pb alloy by using two lateral heat exchangers, allowing extraction of the heat flux from one or two vertical sides of the sample. The domain is a quasi-two dimensional rectangular ingot (100 x 60 x 10 mm). The temperature difference AT between the two lateral sides is 40K, and the cooling rate CR = 0.03 K/s. The instrumentation firstly consists in recording the instantaneous temperature maps by means of a lattice of 50 thermocouples to provide the time evolution of the isotherms. Measurements of the velocity field by ultrasonic Doppler velocimetry (UDV) method in a Ga-In-Sn pool were taken and transposed to the tin-lead alloy case before solidification. After each experiment, the segregation patterns were obtained by X-ray radiograph, and confirmed by quantitative analysis of the solutal distribution obtained by chemical method coupled with the technical ICP (Inductively Coupled Plasma). The originality of the present study is to examine the effect of various types of forced convection driven by a traveling magnetic field (TMF). Three cases of TMF were investigated: in the same direction as natural convection, reversed with respect to natural convection, and periodically reversed with a modulation frequency equal to 0.125 Hz. This study allows us to evaluate the evolution due to the forced convection induced by a TMF field, as well as its influence on the initial conditions, the solidification macrostructure and the segregation behavior. While forced convection promotes equiaxed structures, the stirring pattern influences grain size according to its direction with respect to natural convection. The results show that all electromagnetic stirring modes effectively reduce macrosegregations significantly, while remaining inactive for reducing development of segregated channels.