| Bulk metallic glasses(BMG)have attracted attention due to their extraordinary mechanical properties such as superior strength,hardness and excellent corrosion resistance.However,size limitation,difficulty in applications in combination with other materials and difficulty in processing caused by room temperature brittleness have hindered their potential for structural applications.To solve this problem,connecting small scale bulk metallic glass into large metallic glass may be one of the most effective method.Based on the superplastic forming characteristics of the metallic glass in the supercooled liquid region,novel amorphous LM1B/7075 aluminum alloy composite,LM1B/LM1B connector,as well as the amorphous thin tube were fabricated through the co-extrusion technology.The ranges of extrusion temperature and punch speed were varied from 430 to 450 C and from 1 to 4 mm/min,respectively.The effect of extrusion temperature and speed on joint quality,element diffusion and thin tube quality was studied by a variety of techniques including Differential Scanning Calorimetry(DSC),X-ray diffraction(XRD),Optical Microscope(OM),Scanning Electron Microscope(SEM),and Transmission Electron Microscope(TEM),and the optimum extrusion process parameters were determined.The main results of this dissertation are as follows:(1)Zr-based bulk metallic glass LM1B/7075 aluminum alloy multi-materials have been fabricated by extrusion in the vertical stacking form.The experimental results show that at 440? and 2 mm/min,the extruded joints are straight,free of squeezing flash,and have good surface quality.XRD results showed that the amorphous part of the sample was still in an amorphous state.OM and SEM result showed that an interface of which Al alloy is inserted into BMG and wrapped tightly by BMG in the periphery is obtained,and the interface is smooth,free of holes,inclusions and other defects.some burr-like protrusions appear at the top of the joints,forming a small range of mechanical bonding.TEM results show that the amorphous site maintains a good amorphous state with only a small quantity of nanocrystals appeared within the range of 20 nm at the interface and elemental diffusion occurred at the interface between the amorphous and the aluminum alloy,forming a mechanical as well as metallurgical bonding joint form.The tensile strength of the joint was 429 Mpa,and fracture occurred in the aluminum alloy part,indicating that the joint strength was higher than the aluminum alloy matrix.(2)Zr-based bulk metallic glass LM1B/LM1B connector has been fabricated by extrusion in the vertical stacking form.The experimental results show that higher extrusion temperatures and lower extrusion speeds are conducive to the formation of high quality joints.The extrusion joint obtained under the condition of 440? and 2 mm/min was straight and there were no defects such as squeezing flash,and the surface quality was good.XRD results showed that the connected sample was still in an amorphous state.No obvious interface was observed by means of SEM,indicating the formation of diffusion joint.The tensile strength of the joint is 650 MPa and the tensile fracture shows that the homomorphous amorphous alloy forms a "sleeve" shaped joint,which is similar to the LM1B/7075 interface,and the fracture first occurs at the peripheral"sleeve".(3)By stacking the 7075-LM1B-7075 alloy,thin amorphous alloy tubes were prepared by hot extrusion.The results show that the quality of amorphous thin tubes obtained under different extrusion conditions varies greatly.High temperature and high extrusion speed can lead to defects such as cracking of thin tubes,inclusions,and asymmetry of thin tubes along the axis.The hardness of amorphous thin tubes increases as the extrusion temperature increases and decreases with the increase in the extrusion speed.The amorphous thin tube prepared at 430? and 2 mm/min was found to have the most unifprm wall thickness and clear outline.TEM results show that theamorphous thin tube maintains a good amorphous state. |
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