The atomic configurations play a key role in predicting the solidification process of high-entropy alloys (HEAs). The atomic scale structures of AlxCrCoFeCuNi (x = 0.5, 1.5, 3.0) HEAs that emerge during solidification with a cooling rate of 12 × 109 (K/s) are evaluated using molecular dynamics (MD) simulation. While BCC (body-centered cubic) structure is obtained for Al0.5CrCoFeCuNi and Al1.5CrCoFeCuNi where lattice distortion increases with increasing aluminum fraction from x = 0.5 to x = 1.5, for Al3.0CrCoFeCuNi, an amorphous structure is formed under the same cooling rate. The diffusion coefficient of all the elements at 2200 K and the super-heating temperature of each alloy are evaluated to explain the disordering mechanism due to aluminum addition, which affects both the aluminum mobility and diffusion of the constituent atoms in the HEA. Finally, the compression behavior of all the three HEAs was studied to show the effect of crystalline structure on the stress fluctuation. It was found that phase transformation induced plasticity occurred which led to a secondary hardening of crystalline alloys after ultimate compressive strength (UCS).