Amorphous Al–Mg–B thin films were synthesized via a combinatorial sputtering approach. The properties of Al–Mg–B films with the varying deposition temperature was investigated. The deposition temperature was found to dominate the hardness of the amorphous as-deposited film. The hardness increases with increasing deposition temperature and may even exceed that of crystalline AlMgB₁₄ material. The high hardness may be attributed to the existence of randomly distributed B₁₂ icosahedra structure. Therefore, the thin film that was deposited on cemented carbide shows well-cutting performances in turning Ti alloy bar. At the same time, an appropriate method of pretreatment is the key to ensure the coating tool with the excellent adhesion by impact fracture test.