Effects of the synergistic addition of AlCrNiTi and Ce on the microstructure and mechanical properties of hypoeutectic Al-7Si alloy

Abstract

A new strategy is proposed in this study to modify the microstructure of the Al-7Si alloy, which is widely employed in the aerospace and transportation sectors due to its lightweight, high specific strength, and specific modulus. The primary challenge of the Al-7Si alloy is its coarse microstructure, which undermines its mechanical properties. This research focuses on the effects of adding the AlCrNiTi master alloy and Ce to the Al-7Si alloy. The impact on both the microstructure evolution and the mechanical properties is examined, including analysis and discussion of the underlying mechanisms for refinement and strengthening. When the alloy was modified by 0.9 wt% of the AlCrNiTi master alloy and 0.1 wt% of Ce, there was a notable refinement of the α-Al phase, transforming it from a coarse dendritic structure to fine equiaxed grains. The addition of 0.9 wt% of the AlCrNiTi master alloy and 0.1 wt% of Ce can also reduce the secondary dendrite arm spacing (SDAS) to 5.9 μm. The eutectic Si phase underwent a significant transformation, changing from coarse flakes to fine granularity with rounded edges. Furthermore, CeSi2Ni2, Al3Ni intermetallic compounds, and nanoscale Al45Cr7 particles were observed in the modified Al-7Si alloy. Tensile tests showed that the addition of the inoculant in the Al-7Si alloy enhanced the ultimate tensile strength (UTS) from 173 MPa to 211 MPa and increased the elongation (El) from 7.9% to 14.1%.