Effects of Al–Nb–B grain refiner on the microstructure and cast fluidity of die-casting ADC12 alloy

The microstructure refinement of the materials is the key to improving their comprehensive performance, and adding grain refiner has also become a common means to achieve grain refinement of casting alloys. In particular, microstructure refinement of die-casting Al alloys is more critical for their mechanical properties. This research investigated the effects of Al-Nb-B grain refiner on microstructure evolution, porosity defect, fluidity, and mechanical properties of die-casting ADC12 alloy. The results show that the Al-Nb-B grain refiner exhibited satisfying refining, fluidity enhancement, and room-temperature tensile properties improvement effects on die-casting ADC12 alloy. The average grain size of the mixed grains region and dense with coarse-grains region in the ADC12 alloy were refined from 7.6 μm to 6.3 μm and 13.9 μm to 11.2 μm, respectively, after adding the grain refiner. The secondary dendritic arms spacing (SDAS) of ADC12 alloy also reduced from 12.4 μm to 8.8 μm. The percentage of porosity defects in ADC12 alloys decreased from 1.2% to 0.8% with the refinement. The cast fluidity of the die-casting ADC12 alloy was improved (flow length from 910mm to 1000mm). The improvement of fluidity and mechanical properties is the decrease in solidification interval and liquid phase line temperature, as well as microstructure refinement resulting from the addition of the Al-Nb-B grain refiner.