SHEAR DEFORMATION OF HIGH SOLID FRACTION (GREATER-THAN-0.60) SEMISOLID SN-PB UNDER VARIOUS STRUCTURES

The behavior of high solid fraction (> 0.60) semi-solid Sn-Pb alloys w as studied in pure shear deformation using a Couette geometry rheomete r. Three structures were investigated: a classical coarse dendritic st ructure, a globular structure obtained by reheating a fine dendritic s tructure (R.G.) and a globular structure generated by vigorous stirrin g during solidification (S.G.). The slurries were subjected to shear r ates ranging from 0.01 to 50 s(-1). Experimental data for dendritic st ructure and for R.G. are compared to the model proposed by Nguyen et a l. (Proc. 2nd Int. Conf. on Processing of Semi-Solid Alloys and Compos ites, Boston, USA, 1992, p.296; and Int. J. Plast. 10 (1994) 693). The S.G. structure exhibited a very different behavior compared with glob ular structures obtained from a fine dendritic precursor (R.G.). This behavior is interpreted in terms of an agglomeration/disagglomeration model.