THE ROLE OF MICROSTRUCTURE AND POROSITY IN DUCTILITY OF DIE CAST AM50 AND AM60 MAGNESIUM ALLOYS

摘要

The deformation and fracture behavior of die-cast AM50 and AM60 magnesium alloys have been examined to determine the processes leading to fracture in bending and tension and to elucidate the influences of microstructure and porosity on ductility. Damage accumulation in terms of crack initiation, growth, linking and eventual failure was quantified as a function of strain for as-cast plates with section thicknesses of 2, 6 and 10 mm. Microstructure and porosity distribution are dependent on section thickness, with bands of high porosity resulting from the nature of the die filling process. In both tensile and three-point bend studies, damage accumulation and subsequent ductility at fracture are strongly influenced by the heterogeneous porosity distribution, with early crack formation occurring in regions of highest porosity. A model is presented that relates the observed ductility of these alloys with porosity distribution, crack size, crack tip radius, and elastic modulus.