The effect of magnesium addition on the morphological, thermal, and mechanical features of conventionally and rapidly solidified Al-5.5 wt.%Zn-x wt.%Mg (x = 1, 5) samples were examined in this work. Al-5.5wt.%Zn-x wt.%Mg (x = 1, 5) samples were produced by the conventionally solidified graphite casting and rapid solidification by the melt-spinning method. The morphological and phase structures of the alloys were shown by field emission scanning electron microscopy and x-ray diffractometry. The melting temperatures were examined by differential thermal analysis in an Argon gas environment and the stress and microhardness characteristics of the conventionally solidified and melt-spun ribbons were determined by hardness and tensile strength tests. It was observed that the content of 5 wt.%Mg allowed a radical change in the conventionally solidified alloy morphologies, such as nano-sized dot shape Al12Mg17 particles and smaller sized square shaped MgZn2 particles. Moreover, the ultimate tensile strength, yield strength, and microhardness values of the rapidly solidified Al-5.5Zn-5Mg samples increased by approximately 20%. Finally, it was observed that the microstructural and mechanical properties, such as microhardness/stress values and grain size refinement, were improved with high wheel speeds.