Development of the Elastic Modulus of 100 GPa Casting Alloys by Nickel Addition

In this research, we studied the effects of Ni, Ti, and B on the elastic modulus of hypereutectic Al-Si alloys and successfully synthesized 100 GPa Al casting alloys by designing various alloys phases. Generally, Al–Si based alloys are known in the automotive industry to be good casting alloys with high wear resistance, low thermal-expansion coefficient, good corrosion resistance at a wide range of temperatures, especially for cylinder blocks, cylinder heads, pistons and valve lifters, but the low elastic modulus of the alloys remaines a weakness. Previously, the elastic modulus of eutectic Al-Si casting alloys was enhanced by 10 GPa by strengthening phases with added Ti and B. However, elastic modulus was not enhanced by increasing Si content in the hypereutectic Al-Si alloys, since Si only reacts with the Ti containing strengthening phase. We overcame this problem by adding Ni to Ti and B containing hypereutectic Al-Si alloys. The effects of the strengthening phases produced by the addition of Ni, such as AlNi, AlNiCu, on the elastic modulus were studied, and we observed a two-fold enhancement in the wear resistance of the Ni, Ti, and B containing hypereutectic Al-Si alloys. The rate of strengthening by phases in the alloys was qualitatively analyzed by EPMA (Electron probe micro-analyzer), SEM (Scanning Electron microscopy), etc, and their mechanical properties were quantitatively evaluated by elastic modulus measurement and pin-on tester.