Glass Forming Ability Of Al-Ni-Zr Alloy And Microstructure Evolution And Properties Analysis During Crystallization

Al-based amorphous alloys have great application prospects in aerospace,marine,automotive and other fields due to their lightweight,high strength and high corrosion resistance.However,because its glass forming ability is very sensitive to the element content and poor thermal stability,the preparation of Al-based amorphous critical size has not been a significant breakthrough and limits its large-scale application,so the key to the research and development of Al-based amorphous is to explore the high glass forming ability and excellent performance of the alloy system.Based on the Al-Ni-Zr ternary alloy system,this paper first investigates the atomic structure of alloys with different Zr contents in the liquid and amorphous states through first principles molecular dynamics simulations,and analyzes the reasons for the difference in glass forming ability from an atomic perspective.Subsequently,Al-based amorphous ribbons were prepared by melting and spin quenching methods to verify the accuracy of the simulation results,focusing on the correlation between elemental content,microstructure and properties.Finally,ribbons with high glass forming ability and high performance were heat treated at different temperatures and the influence of the thermal stability of the amorphous ribbons and the structural evolution during crystallization on the properties were analyzed.Al86Ni(14-x)Zrx(x=2,4,6)alloys with different Zr contents were selected for first principles molecular dynamics simulations.The calculation results show that the main peaks of the total pair distribution function curves in the amorphous state all become higher and sharper relative to the liquid structure,and that shoulder peaks appear to the left of the first peak of the curve,indicating stronger interactions between their atoms and a higher degree of atomic shortrange ordering.As can be seen from the Voronoi polyhedra,the type of clusters has changed considerably.In addition,in both liquid and amorphous structures,the Al-Al atom pair of the Al86Ni10Zr4 alloy has a chemical short-range order parameter close to zero,with a more disordered arrangement and a higher glass forming ability.Analysis of Voronoi polyhedra shows that there is a wide variation in the type of clusters centered on individual atoms,with the Al86Ni(14-x)Zrx(x=2,4,6)alloys all having a low content of icosahedra<0,0,12,0>,while at 4 at.%Zr the amorphous alloys have the highest content of icosahedral-like clusters,meaning that the alloy has a higher resistance to crystallization and thus a higher glass forming ability.Amorphous ribbons of Al86Ni(14-x)Zrx(x=1～7)with different Zr contents were prepared by melting and spin quenching method.The phase structure and thermal stability of the ribbons with different compositions were analyzed by XRD,TEM and DSC.The variation of Zr content on the glass forming ability of Al-Ni-Zr system alloys is summarized,verifying the reliability of the simulation results.The addition of Zr elements with larger atomic radius drives the main DSC exothermic peak to higher temperatures and therefore improves the thermal stability of amorphous crystals.At Zr content of 4 at.%,the DSC curve has the highest exothermic peak area and the highest glass forming ability.The results of electrochemical tests on amorphous ribbons with different Zr contents show that all ribbons form a passivation region in 3.5 wt.%NaCl solution and have good corrosion resistance.At Zr content of 5 at.%,the corrosion tendency of the ribbon containing minor nanoprecipitation phase is low and the corrosion rate is the lowest,showing the best corrosion resistance,which is mainly the result of the combined effect of the microstructure of the alloy and the passivating elements.By observing and analyzing the corrosion morphology,it was found that the corrosion of the Al-Ni-Zr ribbon was mainly caused by the presence of dissolved oxygen in the solution as well as reactive anions(e.g.Cl-),which produced corrosion products consisting mainly of aluminum and nickel oxides through crack expansion under the action of internal stress.In addition,the large amount of nano-scale α-Al and Al3Zr precipitated on the matrix has a hardening effect on the alloy and the hardness of the Al86Ni7Zr7 alloy reaches 288 HV.Based on the DSC curves of the Al86Ni10Zr4 ribbon,annealing treatments were selected at different temperatures.The thermal stability and the evolution of the microstructure and corrosion resistance of Al86Ni10Zr4 amorphous ribbon obtained by chilling were investigated.The results show that the crystallization process of Al86Ni10Zr4 amorphous alloy exhibits multistage crystallization behavior and has good thermal stability.After low temperature annealing heat treatment at 523 K,the mixture of nanocrystalline α-Al phase and amorphous matrix can be obtained,corresponding to the increasing of corrosion resistance.The results of the XPS analysis confirm that the corrosion resistance of Al86Ni10Zr4 amorphous alloy is not only related to the disordered amorphous structure,but is highly dependent on the ability to promote the formation of the dense passivation film.