Structure Evolution Of Al-Ni-La Alloy Melts And Its Influence On Solidified Structure

In this work, the melt structure of Al-Ni-La alloy and its changes with temperature andcomponent were investigated through electrical resistivity, liquid X-ray diffraction andviscosity experiment, the temperature-induced liquid-liquid structure changes phenomenonwas also discussed. The rapidly solidified Al-Ni-La alloy and amorphous alloy were preparedby a single roller melt spinning apparatus at different melt temperatures; the structure,microtopography and properties of melt-spun Al-Ni-La alloy were also explored through XRD,SEM, DSC, electric chemical corrosion and hardness test to research the melt feature and itsinfluence on the Al-Ni-La alloy.The resistivity of Al100-xNix(x=0,2,2.7,5) and Al100-xLax(x=2,3,5) alloy melt increaseswith the rise of the melt temperature, and shows a liner change from Tlto a turning pointtemperature and then a non-linear change. The turning point temperature increases with the riseof Ni content and La content respectively, it changes from850oC to950oC in Al-Ni alloy meltand880oC to960oC in Al-La alloy melt. It can be seen from the resistivity-temperature curvesthat some reversible structure features occur in Al-Ni alloy melts, the resistivity in coolingprocess is higher than that in heating process. The resistivity of Al-Ni and Al-La alloy meltincreases with the rise of Ni content and La content, this change tendency is also non-linear.The rapidly solidified Al100-xNix(x=2,2.7,5) alloys and Al100-xLax(x=2,3,5) alloys containamorphous structure when the roller rotation speed is2500rpm after melt-superheatingtreatment. The corrosion resistance and hardness of Al-Ni and Al-La melt-spun alloy increasewith the rise of melt temperature, these properties show a non-linear changes with preparedtemperature and have a relatively large rise during850~950oC and880~960oC respectively.The various tests on melt-spun alloy verify the results of the resistivity and viscosity.The Al84Ni10La6amorphous structure can be obtained at a roller rotation speed of2000rpm when the melt superheat temperature is1020oC. The melt structure becomes uniform,dense and diffuse with the increase of the temperature, and then the melt superheat treatmentenhances the GFA of Al84Ni10La6alloy. The amorphous alloys maintain this uniform and densestructure, as a result, its thermal stability, corrosion resistance and hardness increase with themelt temperature rising. The change tendencies of these properties show a nonlinear relationship with the temperature and a relatively large change between the1220℃~1280℃,indicating the nonlinear and inhomogeneous melt structure change.The structure parameters such as nearest atomic distance and coordination numbers of thecrystal structure, amorphous structure and liquid structure in Al-Ni-La alloy were calculated,the degree of disorder becomes large from crystal, amorphous structure to liquid alloy,accompanying with the increment of nearest atomic distance and coordination number. We tryto study the melt structure and its change from resistivity and the method of remaining part ofthe melt structure features by "freezing" them in the melt-spun alloy with a cooling rate of104~105K/S, these experiment results of melt-spun alloy verify with the experiment results ofthe alloy melt, indicating that this method is useful.According to structure factor and pair distribution function from X-ray diffractionexperiment, the nearest atomic distance, coordination numbers and correlation radius of liquidAl-Ni alloy were obtained. Then based on these structure parameters, we calculate theresistivity and viscosity of Al-Ni liquid alloy according to the Faber-Ziman and Born-Greentheories respectively by utilizing nearly-free electron model, pseudopotential method and L-Jpotential model and so on. The calculated values are consistent with the experimental values.The liquid X-ray diffraction, resistivity and viscosity of Al-Ni-La system alloy melts areconsistent with the XRD, SEM, DSC, electrochemical corrosion and hardness test of Al-Ni-Lasystem rapid solidification alloy and amorphous alloy; meanwhile, the theoretical values ofresistivity and viscosity are consistent with the experimental values. Based on these resultsexplored the melt structure from different aspects, we discuss this melt structure, theliquid-liquid structure change and the relationship between the liquid and amorphous structure,and describe the melt structure of Al-Ni-La system and its variation with temperature.