| Bulk metallic glasses(BMGs)have excellent physical,chemical and mechanical properties at room temperature,such as high strength and hardness,perfect wear resistance and corrosion resistance.As structural materials,BMGs have a promising potential for engineering application.It can replace the existing high-performance metals to manufacture the key working parts of equipment,and it is one kind of engineering materials having a wide application prospect.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.The objective of study is to research the feasibility of preparing dissimilar alloys composites involving amorphous alloys Zr44Ti11Ni10Cu10Be25(LM1B)and magnesium alloys(AZ31B)and aluminum alloys(Al 7075)by stacking extrusion in the SLR,and the properties between dissimilar alloys are also presented.For the LM1B/AZ31B extrusion tests,the ranges of extrusion temperature and punch speed were varied from 430 to 450? and from 1 to 6 mm/min,respectively.A1 7075/AZ31B extrusion tests have been divided into two different parts based on the thickness of thin interlayer LM1B.For the 0.5 mm thin interlayer,the ranges of extrusion temperature and punch speed were varied from 430 to 450? and from 2 to 6 mm/min,respectively,and the thin thickness interlayer of the second kind of extrusion tests is 0.2 mm,the extrusion temperature was limited to the 440?,while the punch speed were varied from 2 to 6 mm/min.The effect of extrusion temperature and speed on joint quality and element diffusion 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)BMGs display a low viscosity for a long time before crystallization at a certain temperature range(SLR),which provides an opportunity for thermoplastic forming.Zr-based bulk metallic glass LM1B/AZ31B magnesium alloy multi-materials could be prepared by extrusion in the vertical stacking form within SLR.The experimental results show that at 440?and 5 mm/min,the extruded joints are straight,free of squeezing flash,and have good surface quality.At the same extrusion speed,different test temperature has a great influence on the complex deformation of LM1B/AZ31B,especially the flow ability of the BMG increases gradually with the increasing of heating temperature.The force increases as the extrusion temperature decreases and increases with the increase in the extrusion speed.The interface between LM1B and AZ31B is well bonded,the boundary shape is smooth and without crystallization of LM1B,holes,inclusions and other defects.The bonding mode between LM1B and AZ31B is mainly mechanical with partial metallurgical bonding.The width of diffusion bonding zone between LM1B and AZ31B is 10-20 nm.The diffusion of a LM1B elements to AZ31B is obvious,and the diffusion of AZ31B element to LM1B is weak.(2)The Al 7075/LM1B/AZ31B composites have been fabricated by hot stacking extrusion method,and the amorphous alloys(LM1B)were used as interlayer.On the average,the Al 7075/LM1B/AZ31B composites reach a length of 80-100 mm,and the extruded samples are straight,free of squeezing flash with a good surface quality.OM and EPMA results showed that an interface of which Al alloy and Mg alloy are well bonded by interlayer LM1B,especially in adopting 0.2 mm thickness amorphous interlayer,the interface is smooth,homogeneous and free of cracks.The tensile strength(350 MPa)of A1 7075/LM1B/AZ31B joint is higher than that of Mg-Al alloy joint without amorphous interlayer(311 MPa). |
PDF Full Text Request