The Influence Of Cold-rolling On Microstructure And Mechanical Properties With LZ91 Mg-Li Alloy

The density of magnesium lithium alloy has been the smallest in metal structure material so far. The magnesium lithium alloy not only has good damping shock absorption, fine dimensional stability, excellent electromagnetic shielding, high-energy particle penetration resistance and other excellent properties, but also it has high rigidity, high specific strength,good toughness at low temperature. This alloy is the ideal structural damping materials in areas such as the aerospace, weapons and equipment, transportation. If this alloy is widely used, it will have significant economic benefits in the aspect of energy conservation and emissions reduction.This thesis studied the cold rolling deformability process of LZ91 Magnesium Lithium Alloy by utilizing experimental methods like metallographic microscope, scanning electron microscope, transmission electron microscope, X-ray diffractometer, hardness test,room-temperature tensile and cup drawing test. The experimental results are as follows:(1) The grains of the as-cast LZ91 magnesium lithium alloy are coarse. The strength of the as-cast LZ91 Mg-Li alloy is 114 MPa, and the elongation rate is only 16.9%. After hot extrusion, dynamic recrystallization is occurred in the structure of the alloy, and ? phase presents equiaxial grain of different sizes. After hot extrusion, the tension strength of the alloy is 164 MPa, and the elongation rate is 28%.(2)With the rolling reduction increasing, the tension strength of hot extrusion LZ91 magnesium lithium alloy increases when it is rolled at room temperature, and its tension strength increases to 267 MPa. The elongation rate descends first, then increases, descends at last. There is no phase changing, no generation of new phase or dissolution of original phase during cold rolling process. Slight change occurs in the relative intension of the diffraction peak of ? phase and ? phase.(3) The ? phase of hot extrusion LZ91 Mg-Li alloy possesses a comparatively strong fiber structure whose basal is parallel to direction of extrusion. While the ? phase possesses a comparatively strong structure which is perpendicular to extrusion direction. After cold rolling, texture intensity of alloy decreases to a lower level. While rolling reduction of alloy is to 95%, texture intensity increases. As for the cold-rolled sheet without intermediate annealing, the structure of ? phase does not change, while the basal texture intensity of ?phase weakens after being processed with 200?/4h annealing.(4) The intermediate annealing test indicates that the optimal choice for alloy annealingprocess is 200?/1h. When the thickness comes to 0.7 millimeters, the tension strength is 224 MPa, and the elongation is 24.8%. The way of tensile failure is ductile fracture. The IE number which is measured by conducting cup drawing test on the cold-rolled 0.7mm sheet without intermediate annealing is 5.56 mm. The IE number changes to 6.23 mm when cold-rolled sheet is tested with intermediate annealing process.(5) The LZ91 sheet without intermediate annealing can meet the stamping property requirement after being processed with 200?/4h annealing. The Vickers hardness number is67, and the cupping IE number is 7.82 mm.