Achieving further refinement of grain structure and improvement of mechanical properties in Al-12Si-4Cu-2Ni-1Mg alloy by Al-Ti-C-B master alloy addition and deep cryogenic treatment

Near-eutectic Al-Si alloys are widely used in automotive manufacturing due to their superior wear resistance and high temperature performance. Because of high Si content, the grain refinement of near-eutectic Al-Si alloy has been a problem for many years. In this study, the effect of deep cryogenic treatment (DCT) on the microstructure and mechanical properties of Al-12Si-4Cu-2Ni-Mg alloy with addition of Al-Ti-C-B master alloy was fully investigated. Results show that the average grain size of the alloy is greatly reduced from 0.92 mm to 0.50 mm, and the eutectic Si and Al7Cu4Ni precipitates are spheroidized and refined in Al-12Si-4Cu-2Ni-Mg after DCT for 24 h and aging treatment. Thereby these changes of microstructures result in a significant increment of about 22.5% in elongation and a slight enhancement of about 6.8% in tensile strength. Moreover, the refinement of microstructure also significantly improves the fatigue life of the alloy.