•Changing Ni content in alloy causes formation of different Ni containing phases.•Formation of Ni containing intermetallics reduce the amount of Al2Cu phase.•Existence Ni bearing intermetallics has a dramatical effect properties of material.•Lower Ni additions are desirable for improving the mechanical properties. Investigations have been carried out to understand the correlation between Ni content and properties of HPDC cast A384 aluminium alloy in as-cast and heat-treated conditions. Depending on Ni content in the alloy, different Ni-bearing intermetallics were formed. Suitable heat treatment conditions were selected after a series of experiments to obtain optimal mechanical properties. Most of the Ni containing intermetallics found to be stable at solutionizing temperatures which have a dramatic effect on the mechanical properties of alloys after natural and artificial aging. The results showed that, after heat treatment, to achieve higher strength values lower Ni additions are favourable.