Study On The Preparation And Crystallization Of Mg-based Bulk Amorphous Alloys

Mg-based amorphous alloys own excellent glass-forming ability (GFA). Mg₆₅ Cu₂₅ Y₁₀ alloy has the largest supercooled liquid regionΔT_x (=T_x-T_g, where T_x and T_g are the crystallization temperature and the glass transition temperature, respectively) and the best GFA in Mg-Ln-TM system. In the present paper, Cu in Mg₆₅ Cu₂₅ Y₁₀ alloy has been replaced by Al-Si and Al-Ti-B alloys. Then, Mg-based amorphous alloy ribbons were prepared by single-roll melt spun method in Ar atmosphere, while bulk metallic glasses (BMG) by copper mold casting method. The amorphous states of Mg-based alloys were confirmed by X-ray diffraction (XRD), Differential Scanning Calorimeter (DSC) and Scanning Electrical Microscopy (SEM). Effects of Al-Si and Al-Ti-B alloys on the GFA and mechanical properties of Mg-based amorphous alloys and crystallization behaviors of Mg-Cu-(A1-Si)-Y amorphous ribbons and Mg-Cu-(A1-Ti-B)-Y BMG were studied.From experimental results, it is showed that the addition of Al-Si and Al-Ti-B alloys affects the GFA and mechanical properties of Mg-based amorphous alloys in different ways. The GFA was found to decrease with increasing subsituent of the above alloys for Cu. However, the ambient-temperature ductility and the microhardness were improved with the addition of either Al-Si or Al-Ti-B alloys.Mg₆₅ -Cu₂₄ -(Al-Si)₁-Y₁₀ amorphous ribbons and Mg₆₅ -Cu₂₄ -(Al-Ti-B)₁-Y₁₀ BMG were isothermal annealed nearby Tg. Some crystalline phases precipitated in the amorphous matrix as the annealing temperature was high enough or the annealing time was long enough. It is revealed that the longer annealing time and the higher temperature, the more the crystalline phases will precipitate. Those crystalline phases have been identified as Mg, Mg₂Cu and some unknown phases. It has also been found that the precipitation of Mg₂Cu grains makes Mg₆₅ -Cu₂₄ -(Al-Si)₁-Y ₁₀ amorphous ribbons very brittle after crystallization. The feature of brittle fracture has been comprehended by the fracture surface images of amorphous alloy ribbons. The microhardness of Mg₆₅ -Cu₂₄ -(Al-Ti-B)₁-Y₁₀ amorphous alloy has been found to increase with increasing annealing time.