IMPACT FRACTURE OF RAPID SOLIDIFICATION PROCESSED AL-LI ALLOYS

The deformation-fracture behavior in impact test of rapid solidificati on processed (RSP) AI-Li alloys has been studied systematically. The r esults show that there are both intrinsic and the extrinsic toughening effects in RSP Al-Li alloys. The intrinsic toughening effect is contr olled by the micro-mechanism of fracture in the alloys, while the extr insic toughening is produced by cracking of the prior powder boundarie s (PPBs). The level of extrinsic toughening effect is determined by th e relative strength of grains, grain boundaries, and PPBs. Large secon dary cracks across the transverse section of impact specimens form eas ily along relatively weak PPBs in the as-quenched condition, leading t o a marked extrinsic toughening effect. However, in the peak aged and overaged conditions, cracks propagate mainly along grain boundaries, a nd the extrinsic toughening effect is inhibited.