Effects of combination of 0.02 wt % Sr and Ti on the characteristics of AC4B alloys produced by low pressure die casting

Aluminium AC4B alloy is widely used in automotive industries for various components. However, when this alloy is used to produce motorcycle cylinder head by Low Pressure Die Casting (LPDC) process, high reject rate was often found due to shrinkage, porosity and misrun. Addition of grain refiner and modifier is an alternative for this problem, through the control of solidification process that results in grain refining and microstructure modification. This study was aimed to investigate the effect of combination of 0.02 wt. % Sr modifier with variation of Ti grain refiner on the characteristics of AC4B alloy and the reject rate of cylinder head components. The Ti grain refiner was varied 0.063, 0.083 and 0.108 wt. % Ti and added at the holding furnace prior to LPDC process. A series of test was conducted including hardness test from the thin and thick regions of the part, tensile test, fluidity test, vacuum test as well as observation of microstructure by using optical microscope and Scanning Electron Microscopy (SEM) equipped with Energy Dispersive X-Ray Analysis (EDAX). The results showed that the higher the Ti content, the higher the hardness for both thin and thick areas, the lower the fluidity of the molten metal. At the maximum level of Ti of 0.108 wt. % and 0.02 wt. % Sr, the reject rate was significantly reduced from 3.59% to 1.38%.