Fabrication of Aluminum Based Bulk Amorphous Hybrid Alloys by Powder Forging

초록

Two types of Al based bulk amorphous hybrid alloys were fabricated by a powder forging process. The starting materials of the TypeⅠhybrid alloy were amorphous Al-10Ni-6Ce (at%) powder (<75 micron) and crystalline pure Al powder (<43 micron). In the Type Ⅱ hybrid alloy, amorphous Al-10Ni-6Ce powder (<75 micron) and crystalline Al-8Fe-2Mo-2V-1Zr (at%) powder (<50 micron) were used. According to phase analysis by differential scanning calorimetry (DSC), crystallization of the amorphous Al-10Ni-6Ce alloy was characterized by a glass transition with onset at Tg=282℃ followed by an exothermic event at Tx=297℃. The amorphous Al-10Ni-6Ce powder was mixed with pure Al powder (Vf=0.3, TypeⅠ) or Al-8Fe-2Mo-2V-1Zr powder (Vf=0.3, Type Ⅱ) using a V-type mixer. The powder mixtures were pre-compacted by cold pressing. Microstructural observation on the both types of pre-compacted mixtures confirmed the uniform distribution of crystalline powders surrounding amorphous Al-10Ni-6Ce matrix. The pre-compacted mixtures were then isothermally forged at temperatures from 250 to 450℃ with the maximum pressure of 660MPa and the average strain ratio of 10-2s-1 in order to achieve the rod-shape bulk hybrid alloys having 10mm diameter. For the both type of bulk hybrid alloys, fully dense structure with the porosity less than 1.5% was observed in the samples forged at and above 375℃, although there existed a number of pores in the samples forged at and below 290℃. Cylindrical compressive specimens of 3.5mm diameter with 5mm gage length were prepared by mechanical machining from the forged rods. Compressive test was carried out using an Instron testing machine in air at room temperature with the strain rate of 1x10-3s-1. Considerably high fracture strength of 1.2GPa with the plastic strain of 1% was obtained in the TypeⅡ bulk hybrid alloy forged at 375℃. The TypeⅠbulk hybrid alloy forged at 450℃ possessed the fracture strength of 0.5GPa and the plastic strain of 2%.