Effect of Nickel Addition on Precipitate Microstructures and Strength at an Elevated Temperature in Wrought Al-Si-Cu-Mg Alloys

Al-Si-Cu-Mg-(Ni) alloys are used for engine pistons or compressor scrolls due to their excellent heat and wear resistance. Although these components are typically produced using mold-casting or die-casting techniques, forging techniques have recently attracted attention because they allow for a lightweight design. However, wrought Al-Si-Cu-Mg-(Ni) alloys have rarely been investigated, and the effect of nickel on precipitate microstructures and strength remains unclear. Here, we investigated the precipitate microstructure and strength at 473 K of wrought Al-Si-Cu-Mg alloys with different nickel concentrations. The 0.2% proof stress and tensile strength decreased with increasing nickel concentration. The TEM observations showed that the decline was attributed to the decrease in the θ' phase. The increase in the Al7Cu4Ni and Al-Fe-Cu-Si-Ni phases suggested that the nickel decreased the θ' phase by consuming the copper in the matrix. In addition, the HRTEM observation revealed the difference in the orientation relationships of the Q phase between with and without nickel alloys. The Q phase observed in the 2%Ni alloy had a smaller lattice misfit with the matrix than that observed in the 0% Ni alloy, indicating excellent thermal stability.