Analysis of Ni-Cu Interaction in Aluminum-Based Alloys: Hardness, Tensile and Precipitation Behavior.

The present work was aimed at quantifying the effects of Ni addition in the range of 0-4% together with 0.3%Zr on the hardness and the tensile properties, volume fraction of intermetallics, and changes in size and distribution of phase precipitation in Sr-modified Al-9%Si-2%Cu-0.6%Mg cast alloys. The study was mainly carried out using high-resolution FESEM and TEM microscopes equipped with EDS facilities. Samples were solidified at the rate of ~3 °C/s and examined at different aging conditions. The investigations are supported by thermal analysis carried out at a solidification rate of ~0.8 °C/s. The results revealed that the main compositions of the Ni-based phases are close to Al(Ni,Cu), AlCuNi, and AlNi. An AlNiCu phase was also detected in the 4%Ni alloy. The Cu-Ni phases were observed to precipitate, covering the surfaces of pre-existing primary AlZr particles. The TEM analysis indicated the magnitude of the reduction in both size and density of the precipitated AlCu phase particles as the Ni content reached 4%, coupled with a delay in the transition from coherent to incoherency of the AlCu precipitates.