Hot chamber is an ideal process to produce small and medium size magnesium castings due to the minimum temperature loss. AM60B is used to produce complicated automotive steering parts because of its good ductility. This characteristic comes from its special microstructure. The AM60B matrix in the hot chamber process is characterized by non-dendrite crumbling α magnesium crystals, which is surrounded by divorced β, Al{sub}17Mg{sub}12 eutectics. Because rapid solidification occurs during the fast metal filling in the die casting process, the β eutectics refuse to form a coarse laminar structure. This structure results in an increase in the ductility and creep resistance. The morphology of the crumbling a primary magnesium structure is a cross between the dendrite and spheroid shape, the latter being normally found in the semi-solid rheological process. The forced heat convention when the molten magnesium is squeezed through the hot chamber gooseneck channel is one of the main reasons. Due to a lower aluminum content than AZ 91D, the AM60B melting flow provides much lower fluidity during the die filling. Because AM60B starts to solidify very early (much earlier than AZ 91D), the casting skin has frozen before the center section solidifies. Furthermore, the AM60B completes solidification very late because of the large freeze range. Therefore, the internal layer defect usually occurs in the magnesium die casting process. These separated internal layers develop to defect bands. It demonstrates a structure difference between the casting surface and core area. The cause of the defect relates to both filling and solidification processes. Practice has shown better gating and casting geometry design can possibly avoid the defect.
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