Abstract
Wrought Mg AZ31 alloy was near-net-shaped by semisolid rheo-diecasting. Parts with 42% and 61% solid fraction were produced at different injection velocities. The impact of injection velocity on the microstructure and the tensile strength of samples have been investigated. Results indicated that the shape factor and the particle size of primary α-Mg in the microstructure decreased with the increase of injection velocity, and the morphology of both secondary α-Mg and eutectic α-Mg + Mg17Al12 mixture were refined with the increase of injection velocity. The surface liquid segregation in the sample closely relates to the injection velocity and the solid fraction of slurries, and it decreased with the increase of injection velocity and the decrease of the solid fraction. Cold shut, crack, and gas porosity were the main internal defects that rely on the injection velocity. The tensile strength of the samples decreased with the increase of injection velocity, and the best value of 201 and 192 MPa was obtained at 0.5 m/s and 1 m/s for the sample with the solid fraction of 0.61 and 0.42, respectively. This work demonstrated a predominant effect of internal defects on the property of the rheo-diecasting (RDC) product than the microstructure; thus, defect reduction should be preferentially considered in the optimization of the RDC process.
Highlights
Semisolid forming (SSF) uses metal slurry containing a certain fraction of the fine and spherical solid phase as the initial material for mold forming
Wrought Mg AZ31 alloy was used as an experiment material for rheo-diecasting; the
Wrought Mg AZ31 alloy was used as an experiment material for rheo-diecasting; effect of injection velocity on the microstructure and tensile strength of this alloy have been investigated
Summary
Semisolid forming (SSF) uses metal slurry containing a certain fraction of the fine and spherical solid phase as the initial material for mold forming. Because SSF offers a promising way to solve problems that are encountered by conventional shaping of wrought alloys such as the poor castability and the cast defects, many studies have been focused on the manufacturing of wrought alloy components by SSF [2,3,4] Wrought magnesium such as Mg–Al series alloys has broad application prospects in the industry of aerospace, and vehicle and consumer products, because of the advantages of low density, high specific strength, and good dimensional stability [5]. Casting these alloys directly into net shape components by using SSF technology has many economic benefits. Zhen et al investigated the semisolid rheo-diecasting (RDC) of the AZ61 alloy, and demonstrated that RDC imparts excellent
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