Most bulk metallic glass systems with high glass-forming ability are doped with precious metal(s) or toxic element(s), like palladium and beryllium, leading to relatively high cost or low safety in use. In this work, the glass-forming ability, crystallization kinetics and mechanical properties of the Zr ₅₅Co ₂₅Al ₂₀ and Zr ₅₂Co ₂₅Al ₂₃ bulk metallic glasses prepared by water-cooled copper mold suction casting are investigated in detail. The results show that Zr ₅₂Co ₂₅Al ₂₃ has a wider supercooled liquid region, a higher thermal stability and a higher glass-forming ability than the Zr ₅₅Co ₂₅Al ₂₀ amorphous alloy. At the same time, Zr ₅₂Co ₂₅Al ₂₃ has a higher activation energy of crystallization than Zr ₅₅Co ₂₅Al ₂₀ amorphous alloy, indicating that Zr ₅₂Co ₂₅Al ₂₃ has a higher resistance to crystallization than Zr ₅₅Co ₂₅Al ₂₀. Investigation of the mechanical properties reveals that Zr ₅₂Co ₂₅Al ₂₃ also has a higher fracture strength of up to 2308 MPa and a higher specific fracture strength of up to 3.78 × 10 ⁵ N m kg ⁻¹ compared with 316L stainless steel, Ti-6Al-4V, as well as Mg-, Ti-, and other Zr-based BMGs.