HIGH-PRESSURE DIE-CASTING - EFFECT OF FLUID-FLOW ON THE MICROSTRUCTURE OF LM24 DIE-CASTING ALLOY

The effect of fluid flow rate on the microstructure of LM24 high press ure die-casting alloy was studied using a fully controlled cold chambe r high-pressure die-casting machine and casting a series of rectangula r coupons of 65 x 130 x 4 mm. All castings showed a bimodal distributi on of dendrites in which the morphology of dendrites was completely di fferent to the classic tree shape characteristic. The large dendrites, which have been shown to come from the wad or runner sections (M.R. G homashchi, Scand. J. Met., 22 (1993) 61-67), are mostly spheroidals al though some rosette morphology may be detected within the central regi ons. It was found that the gate velocity influences the quality of the coupons surface finish, porosity size and percentage, volume fraction and size of both small and large dendrites, which has no effect on th e silicon morphology and percentage of Al-Si eutectic.