Improving the mechanical properties of high pressure die-cast (HPDC) components through T6 heat treatment is still a challenge due to surface blistering. In the current study, theoretical formulation of porosity growth in cast aluminum, EN AC 43100, has been developed along with differential scanning calorimetry and wave dispersive spectrometry to determine temperature ranges of phase transformations and Al-matrix enrichment of solutes. Optimal combinations of time and temperature for maximum possible Mg dissolution in the Al-matrix without blistering as well as tensile testing on samples extracted from HPDC components and samples from the gradient solidification technique that offers samples with low porosity levels have been performed. The results demonstrate that even if the Mg level in the Al-matrix increases and no blisters on component surface are apparent, the strength outcome is limited and can be degraded. Consequently no guarantees are granted that with a seemingly well performed T6 treatment, strength improvement will be realized.