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.