Study On The Preparation And Mechanical Properties Of Mg-Y Alloys

Rare earth elements or yttrium can activate the non-basal slip, reduce the stacking fault energy, weaken the strong basal textures of magnesium sheets and improve the sheet formability, which will expand the application field of the Mg alloys.Several Mg-xY alloys were prepared using pure Mg (99.95%), master alloys containing Mg with 23.5% Y. The Mg-xY alloys were melted in a steel crucible using a resistance furnace with anhydrous lithium chloride and anhydrous lithium fluoride compounds as the coating agent and argon shielding. The microstructure of alloys was observed by optical microscopy (OM), the originally polished surface was then observed in the SEM using the EBSD technique. The deformation mechanism and fracture mechanism of the alloys was analyzed and discussed, and the microstructure evolution during impact process and rolling was studied in detail. The main results acquired are listed as followed:The ultimate tensile strength, tensile yield strength, impact toughness and elongation of Mg-1.5Y alloy after rolling increased. The similar results were observed in pure Mg, except for the impact toughness. In the rolling samples, the ultimate tensile strength, tensile yield strength, impact toughness and elongation of Mg-1.5Y alloy was a little higher than pure Mg. The impact curve of the four samples with different state was similar and no obvious plastic deformation in impact the process. The curve slowly declined after reaching the maximum load, which did not produce instability crack.After the impact test, EBSD analysis was carried out on the samples. The number of twin decreased in as-cast pure Mg and Mg-1.5Y alloy. Similar results were obtained in rolling of Mg and Mg-1.5Y alloy. In the deformed sample, distinguished boundary misorientation peaks crystal coordinate system were shown that in the range 2°-15° of as-cast Mg and as-cast Mg-1.5Y alloy increased after annealing, while in the range 80°-90° were much weaken. In the rolling samples, distinguished boundary misorientation peaks in the range 2°-15° of rolling Mg-1.5Y alloy were strengthen than Pure Mg, while the peaks in range 80°-90° were weaken. This is because that the addition of Y reduced the value of c/a in Mg alloys, and activates the non-basal slip.The annealing is adopted in the process of cold-rolling in Mg-3.7Y alloy. Comparing with the methods of 60 minutes annealing, the number fractions of twin increased with the methods of 30 minutes annealing, while the ultimate tensile strength, tensile yield strength and elongation decreased.The rolling schedule entailed preheating all samples to 450℃ for 5 minutes, followed by total 80% reduction in one pass at 450℃. All samples were subsequently annealed at 400℃ for 0.5 h and 1h. Each alloy produced a recrystallized microstructure with a grain size of 3μm in original grain boundary and Twin boundary. The ultimate tensile strength and yield strength decreased, while the elongation percentage raised gradually with the increase of annealing time.