It investigates the function of Si content at lower level on the precipitation behaviour in terms of hardness, resistivity, impedance, X-ray diffraction analysis, differential scanning calorimetry along with structural transformation of Al-based automotive alloys. Conventional metal cast alloys are subsequently allowed to T6 thermal treatment at progression of homogenizing, solutionizing, quenching and ageing. Solution treated samples are aged naturally and artificially, including isochronal and isothermal for different time and temperature. The results suggest that the formation of clusters and GP zones together with metastable phases leads to considerable hardening in aged alloys. As a result, electrical resistivity also increases but decreases at higher ageing temperature for stress relieving followed by metastable phase dissolution and coarsening of fine precipitation. DSC and XRD study confirms the formation of such phases, showing the different peaks. The Si addition entirely changes the precipitation peak of the base alloy for its increasing properties of heterogeneous nucleation and diffusion kinetics in concert with the Si-rich intermetallic. Microstructural observations confirm that solution treatment improves grains distribution and Si additions creates the eutectic phases and coarsens the alloy grain boundaries. Both alloys as well attained more or less entirely re-crystallized after ageing at 350 °C for 60 minutes.