Quantitative Experimental Study of Defects Induced by Process Parameters in the High-Pressure Die Cast Process
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ERNING the emission of greenhouse gasses as well as the reduction of fuel consumption, the automotive industry is driven to seek lightweight solutions in the development of robust components. Magnesium is a good candidate for this purpose due to the excellent strength-to-weight ratio.[1–5] Many of the complex magnesium components are produced through the high-pressure die casting (HPDC) process, due to its much faster production rate compared with other casting methods, while it is an economic and efficient method for producing components with high-dimensional accuracy. However, the application of die cast magnesium alloys in vehicle structures is limited by variations in the mechanical properties of geometrically complex components.[2] The variations in mechanical properties have been found to depend upon casting defects such as gas and shrinkage porosities, defect band, and externally solidified crystals (ESGs).[6,7] These defects adversely affect the mechanical properties of die cast magnesium alloys,
P. SHARIFI and J.T. WOOD are with Western University, 1151 Richmond Street, London, ON, N6A 3K7, Canada. Contact e-mail: [email protected] J. JAMALI is with American University of the Middle East (AUM), 220 Dasman, 15453, Eqaila, Kuwait. K. SADAYAPPAN is with CanmetMATERIALS, 183 Longwood Rd S, Hamilton, ON, L8P 0A5, Canada. Manuscript submitted April 5, 2017.
METALLURGICAL AND MATERIALS TRANSACTIONS A
such as ductility and yield strength.[6–8] Previous studies reported that the amounts of defects show dependency on the process parameters such as melt temperature, gate velocity, die temperature, intensification pressure, casting geometry, slow stage of piston velocity, and fast stage of piston velocity, and venting gate area.[8–11] Dargusch et al.[9] investigated the effects of intensification pressure and casting second-stage velocity on the volumetric porosity for complex geometry of die cast aluminum alloys. The authors concluded that the increase in the intensification pressure reduces total volumetric porosity; on the other hand, the increase in the second-stage velocity significantly increases volumetric porosity. Other studies[8,12,13] confirm that the ductility of aluminum and magnesium alloys depend primarily upon the area fraction of porosity rather than on the volumetric porosity. Thus, volumetric porosity is not a suitable characteristic for studying the effects of process parameters on the defect formation. Haung et al.[10] studied the effects of intensification pressure, and the first- and the second-stage piston velocities on the total area fraction of porosity for a simple geometry of die cast magnesium alloy. They considered shrinkage and gas porosities together as total area fraction of porosity, while there is a difference in their formation mechanisms. Shrinkage porosity forms during solidification due to the volumetric contraction associated with the liquid-to-solid transformation. On the other hand, trapped air, created by turbulent flow and rapid mold filling during HPDC process, is the main source of gas poros
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