| 其他摘要 | As a new kind of engineering material, the metallic glasses can be used widely due to its excellent properties on strength, hardness, elastic energy and corrosion resistance. The size of metallic glass is generally small, which is the main limitation for the application of metallic glass. How to prepare larger size metallic glasses becomes our main target in present research. One method is optimizing the chemical composition to get larger size metallic glass; and the other is joining the small size metallic glasses together to become larger one in welding way. In this paper, the mechanical behaviors of bulk metallic glass Zr55Al10Ni5Cu30 under high temperature were studied at first. According to its mechanical behavior in supercooled liquid region, the bulk metallic glass Zr55Al10Ni5Cu30 was welded using friction welding, friction stir welding and laser welding. The microstructure and mechanical properties of welded zone were also investigated to verify the welding reliability. The main results are as follows:
In supercooled liquid region, the plasticity and viscosity of Zr55Al10Ni5Cu30 metallic glass are very excellent, and the stress of the uniform plastic deformation was low, the storage modulus fell off 96% than that in amorphous state, and loss factor reached to above 2.34, and the metallic became very soft; when increased the frequency, the metallic glass became hard.
Using friction welding, when the main shaft speed is 4000~5000rpm, the friction pressure is 80~100MPa, friction time is 0.2~0.4s, the upsetting force is 200MPa and the weld time is 2s, the metallic glass Zr55Al10Ni5Cu30 can be welded successfully. The results of X-ray diffraction, SEM and TEM showed that the welded zone remains amorphous state. Zr55Al10Ni5Cu30 bulk metallic glasses were not welded together by friction welding to commercial crystalline materials such as copper and aluminum.
The metallic glass and pure aluminum can be welded successfully using a friction stir welding method. The rotation speed of pin, welding pressure and welding speed are the main factors to control the properties of the welded zone. Investigations on the welded zone indicated that the structure is the mixture of metallic glass and aluminum, the metallic glass is still amorphous state, and the crystal grain of aluminum is refined. The hardness of the welded zone is two to nine times harder than pure aluminum, and strength is higher obviously than aluminum. The fracture occurs on the edge of the aluminum, and is classical ductile fracture.
The metallic glass could be welded by laser welding produced by carbon dioxide. With welding power of 1100-1200W, welding speed of 5-6m/min, the 2mm thick metallic glass can be welded well. An investigations result indicates that the formation of the weld zone was well, and there are no deficiencies like gas cavity and inclusion. The structure of the weld zone is composed by amorphous alloy and less of crystals, on heat-affected zone, there is part of crystals. The hardness of the base metal, heat-affected zone and the welded zone are the same. The strength of the welded zone is two third or four fifth of the base metal, the fracture occurs on the weld zone and is normal fracture. The crack origins from heat-affected zone and the pattern of the fracture are vein-like. |
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