Solidification Microstructure and Critical Conditions of Shrinkage Porosity Generation in Die Casting Process of JIS-ADC12 (A383) Alloy

Abstract

Differential thermal analysis (DTA), analyses of unidirectional solidification process and die casting process, and computational numerical simulations were conducted for JIS-ADC12 (A383) alloy to investigate the generation conditions of shrinkage porosities which occasionally appear in JIS-ADC12 die castings and affect the quality of products. The crystallization temperature of the primary alpha phase and Al­Si binary eutectic phase are estimated to be 856 and 838K from DTA, respectively. The multi-phase eutectic reaction of JIS-ADC12 alloy starts from 826K, and finishes at 801K. The primary alpha dendrites are clearly observed in the unidirectional solidification microstructures, and the relationship between the secondary dendrite arm spacing ­2 and the local solidification time ?f is expressed by the following equation: ­2 ¼ 6:45? 0:31 f . The primary alpha dendrites are also observed in the die cast sample. The average cooling rate estimated from ­2 is approximately 60K/s at the depth of 0.5mm from the surface of die castings. The computational numerical simulation reveals that the values of solidification parameter G= ffiffiffiffi R p increases around the surface of the JIS-ADC12 die castings in where the amount of shrinkage porosities decreases. Especially, shrinkage porosities of the size lager than 200µm is observed when the value of G= ffiffiffiffi R p is less than or equal to 1.4K 0.5 s 0.5 /mm. [doi:10.2320/matertrans.F-M2013806]