Optimization And Characterization Of LM24 And Magsimal-59 HPDC Alloys Under Intensive Shearing

High pressure die casting (HPDC) [1-9] is a fast and economical near-net shape manufacturing method to produce engineered metal parts by forcing molten metal under high pressure into permanent metal moulds. It is widely realised for casting aluminium alloys, magnesium alloys, and zinc alloys, and its applications are normally used in automotive, electrical, electronic and household parts. The careful control of the injection of the melt and the die filling in HPDC are essential to the quality of the final castings. Melt filling which is not under proper control can result in the formation of defects such as ESCs, porosity and shrinkage which can dramatically reduce the mechanical properties of the casting.In this thesis, LM 24 step die MC-HPDC parameters are optimal, with respect to porosity, at 60% filling pressure, 200mm filling position, and 70 bar trigger pressure for a processing temperature of 630°C. From the optical micrograph results the dendritic structures in the sheared sample are reduced which could have a potential benefit for the mechanical properties of the casting. Intensive melt shearing can achieve a more homogeneous microstructure but some undesired inclusions and porosity are also observed in the Magsimal-59 sheared sample microstructure. Electron microscopy is required to investigate the inclusions further. RPT results indicate that intensive shearing has a beneficial degassing effect on Magsimal-59.Both sheared and lower pouring temperature cast samples have a higher ESCs area percentage.Shearing and a lower melt pouring temperature reduce the defect band thickness with the outer defect band location migrating towards the centre of the sample. Un-optimised HPDC processing parameters resulted in the casting sample having lower elongation than specified in the literature.