Investigation Of Mg-based Amorphous Alloys And Their Composites

Mg₅₉Ni₁₂Cu₁₅Nd₁₄, Mg₆₀Ni₁₀Cu₁₅Nd₁₅, Mg₆₀Ni₁₀Cu₁₆Nd₁₄ and Mg₆₁Ni₈Cu₁₆Nd₁₅ alloys were prepared by copper mould casting, the microstructure and mechanical property were analyzed. The results show that GFA (glass forming ability) for those alloys is not lower than 3 mm in diameter. The compressive strength of alloys was all above 600MPa. Furthermore, it was found for the first time that the plasticity up to 8.5% was obtained for Mg₆₀Ni₁₀Cu₁₆Nd₁₄ bulk metallic glass with 3 mm in diameter.Mg_45+xZn_20-xNi₂₀Nd₁₅ (x=0, 5, 10, 15) alloys were fabricated by copper mould casting, the results shows that GFA of Mg₆₀Zn₅Ni₂₀Nd₁₅ alloy is the highest when x=15, and the critical diameter is 2mm.Mg₇₇Ni₁₂Zn₅Y₆ amorphous alloy matrix composite was prepared by replacing Cu with Ni in Mg₇₇Cu₁₂Zn₅Y₆ alloy. The results show that their microstructure is similar, in which Mg phase and other phases are uniformly distributed in amorphous matrix. The as-cast Mg₇₇Ni₁₂Zn₅Y₆ alloy with more amorphous phase shows higher fracture of 580MPa and plasticity of 8%.Mg_77+xNi_12-xZn₅Y₆(x=0, 2, 4), Mg_73+xNi₁₂Zn₅Y_10-x(x=0, 4, 8) and Mg₇₇Ni₁₂Zn_9-xY_2+x (x=0, 2, 4) amorphous alloy matrix composites were fabricated by copper mould casting. The effect of Ni,Zn and Y on the microstructure and mechanical properties of Mg-Ni-Zn-Y amorphous alloy matrix composites were analyzed. The results show that with the decrease of Ni content, the quantity and dimension of Mg phase increases. When the Ni content is 8%, the plastic strain up to 21% was found. However, the strength is only 550MPa due to its low content of amorphous phase. While Mg and Mg₂Ni phases are uniformly distributed in amorphous matrix for Mg_73+xNi₁₂Zn₅Y_10-x(x=0, 4, 8) alloys. With the decrease of Y content, the needle-like Mg phase become thick and more Mg₂Ni particles appears. The compressive tests show that the highest strength up to 812MPa can be found for Mg₇₃Ni₁₂Zr₁₅Y₁₀ alloys, while the plastic deformation up to 8% is for Mg₇₇Ni₁₂Zn₅Y₆ amorphous composite. Mg_73-xNi₁₂Zn₅Y_10-x(x=0, 4, 8) alloys can be cast into amorphous matrix composites, wherein Mg and Mg₂Ni phases are distributed in it. While the amorphous matrix and Mg solid solution is the main crystalline phases for Mg₇₇Ni₁₂Zn₅Y₆ alloys. The mechanical properties are determined both by the microstructure and phase constituents. The fracture strength and plastic strain are 580MPa and 4.5% for x=0, 626MPa and 0.4% for x=2, 571MPa and 8% for x=4 respectively. The high strength and strain are discussed in term of microstructure and shear bands formation in the composites.