Precipitation sequence in high purity Al-Ni dilute alloys by resistivity measurements

Precipitation sequence in high purity Al-250 ppm Ni alloy aged at various temperatures ranging from 253 to 823 K was studied by means of resistivity measurements and transmission electron microscopy. On aging at temperatures below about 600 K, the resistivity decreased in three stages accompanying aging time. The first stage was attributed to the annihilation of quenched-in vacancies, and the second and third stages were attributed to the precipitations of metastable phase Al9Ni2 and stable phase Al3Ni, respectively. However, above 600 K, the resistivity decreased apparently in one stage, which was attributed to the precipitation of Al3Ni. The TTP diagram obtained from resistivity changes was constracted from two C-curves which intersected at about 600 K. This temperature will give the upper limit of the formation of metastable phase. By using 0, 100 and 250 ppm Ni alloys, the relationship between as-quenched resistivity and Ni content and, furthermore, the solvus curve of Ni in Al were given.