Research On Grain Refinement Performance Of A356 Alloy With Zr Based Amorphous Master Alloy

A356 alloy is the most widely used casting alloy in wheel industry,but the coarse grain and needle eutectic silicon in alloy microstructure,resulting in a decline in the mechanical properties of the alloy.The most effective measures to improve the mechanical properties of A356 alloy is master alloy.However,the refinement effect of Al-5Ti-1 B master alloy in application is not ideal,it can't meet the requirements.Therefore we need to find a new kind of master alloy,which can refine grain and improve alloy's mechanical properties.In this paper,we study the refinement of a series of Zr base amorphous alloy.The samples were characterized analysis by using optical microscope?OM?,scanning electron microscope?SEM?,EDS energy spectrum,X ray diffraction?XRD?,transmission electron microscope?TEM?,X-ray diffraction?XRD?,differential thermal analyzer?DSC?analysis method.The mechanical properties of A356 alloy refined by different master alloys were tested using the testing machine and The mechanical properties of A356 alloy were tested by using the Electro-mechanical universal testing machine and Vivtorinox hardness tester.The results are as follows:?1?Because of the multi-component amorphous alloy,increasing the Al intermetallic compound formation probability.Random dense pile structure of amorphous alloy was destroyed,make the alloy composition deviates from the eutectic point which promote the nucleation.Also the multi-component promotes the system entropy,increase the solid-liquid interface energy,at the same time the increase of liquid viscosity can inhibit the atomic long-range diffusion,inhibited the,all of them lead to the refinement of grain;?2?The TiAl₃ phase was surrounded by Al₃(Ti_1–x Zr_x)phase with an obvious gradient transition zone.The amount of Zr in Al₃(Ti_1–x Zr_x)phase is low.As the lattice constant of Al₃(Ti_1–x Zr_x)is closed to TiAl₃,it can promote effectively the nucleation of ?-Al phase.?3?Under a certain temperature and concentration,the Zr and Al would form Al₃ Zr groups,hence reduce the activation energy of nucleation,and promote the formation of crystal nucleus.Furthermore,the grains are refined.In addition,thepinning effect of Al₃ Zr phase on dislocation and grain boundary would strengthen the alloy.?4?With increasing Zr₅₆Co₂₂Al₁₆Ag₆ amount,the mechanical properties of alloy are improved.The tensile strength and yield strength increase by 7.0% and 3.3%respectively and the elongation increases by 64.4% for 0.4wt % Zr₅₆Co₂₂Al₁₆Ag₆ amorphous ribbon addition.With the extension of holding time,the tensile strength,yield strength and elongation decrease.?5?In the pure A356,the grain size of as cast microstructure of 0.4wt%Zr₅₆Co₂₂Al₁₆Ag₆ is further refined,the tensile strength,yield strength and elongation is respectively 319.46 MPa 264.03 MPa and 4%,compared to the A356 aluminum alloy,the tensile strength,yield strength and elongation are increased by 9.16%,3.16% and89.57% respectively.