Papers by Author: Frank Czerwinski

Abstract: Fundamentals of semisolid metal molding, including the particulate feedstock, methods of its generation and features that make it useful for processing, are outlined. Melting characteristics of the feedstock under sole influence of heat are considered, covering a wide range of microstructural and microchemical factors, believed to be of importance at high temperatures. The generation of the thixotropic slurry within the injection molding system and its solidification behaviour are accompanied by detailed features of the molded structures and their correlation with properties of net-shape components. In addition to conventional techniques the novel processing concepts including near-liquidus molding, semisolid extrusion molding as well as the alloy and composite generation in a semisolid state are described. An update on commercialization progress is completed by a characterization of the modern equipment used for process implementation with broad references to metal die casting and plastics injection molding.

Abstract: The conventional and novel routes of injection molding magnesium alloys are described, including thixo- and rheomolding, semisolid extrusion molding, near-liquidus molding, composite molding and alloy generation by mixing thixotropic slurries. For each technique the basic concepts along with their experimental verifications are explained. The examples show the universal nature of the injection molding and its capability of implementing a variety of modern processing methods.

Abstract: Transmission electron microscopy (TEM) was used to assess the microstructural changes accompanying semisolid molding of a creep resistant Mg-5%Al-2%Sr alloy. It was revealed that the processing created thixotropic morphologies with globular solids of α-Mg, having well-developed sub-structures. The quickly-solidified liquid fraction, enriched in Al and Sr, led to the formation of increased volumes of a lamellae type Al4Sr phase, surrounding the secondary α-Mg. Traces of Mg17Al12 still existed, predominantly as irregular shape compounds located mainly in grain interiors. Both the primary solid and high melting point precipitates of Mn-Al modified with Sr, acted as nucleation substrates for secondary α-Mg grains.