Study On Hot Tearing Behavior And Mechanism Of Mg-Y-Ni Alloys

Magnesium alloys are widely used in production and life due to their excellent mechanical and mechanical properties.In recent years,domestic and foreign scholars have studied the mechanical properties of Mg-Y-Ni alloys and found that controlling the appropriate Y / Ni ratio in magnesium alloys can significantly improve the mechanical properties of the alloys,but there are few studies on their hot tearing susceptibility.In order to further study the mechanism of the hot tearing susceptibility of this series of magnesium alloys,this article discusses gradually increasing the Ni content under the same Y / Ni ratio,and studies and analyzes the influence of the hot tearing susceptibility of Mg-Y-Ni alloys.The traditional Mg-Y-Zn alloys are compared,and Ni is gradually substituted for Zn,and the differences in hot tearing susceptibility and microstructures between different alloys are discussed.Based on the Clyne-Davies theoretical model and Newton baseline method,the Mg-2x Y-xNi alloys(x = 0.5,1.0,1.5,2.0,2.5 wt.%)and the Mg-6Y-(3-x)Zn-xNi(x = 0,1.0,2.0,3.0 wt.%)alloys for quantitative analysis.The CSC(Cracking susceptibility coefficient)is used to predict this trend,and this trend is further verified by the size of the hot cracks of the "T"-shaped castings.Use the "T" type hot tearing mold test system to collect data on the solidification shrinkage stress and solidification temperature changes with time of different alloys and draw them into graphs.XRD and SEM are used to analyze the phase composition of the hot tearing microstructure and the morphology of the hot tearing fracture of the alloy with different composition,and combine the TEM image and the diffraction spot of the corresponding selected area to analyze the type of precipitated phase,lattice constant,etc.Analyze the sensitivity of alloy hot tearing.The EBSD detection method was used to study the influence of the Mg-6Y-(3-x)Zn-xNi alloys grain microstructure,grain size,grain axis ratio and grain growth orientation on the alloys hot tearing susceptibility.The results show that with the increase of x,the hot tearing susceptibility of Mg-2x Y-xNi alloys gradually decreases,and the tendency of the matrix α-Mg grain refinement and equiaxation increases with the increase of x,the time of the feed phase of the residual liquid phase between the dendrites is gradually shortened,which is one of the important reasons for the reduction of the hot tearing susceptibility of Mg-2x Y-xNi alloys;With the increase of x,the amount of residual liquid phase between the crystals in the alloy solidification process gradually increases,which has a better feeding effect on the solidification of the alloys,and the precipitation amount of the LPSO phase which has a coherent relationship with the parent phase α-Mg gradually increases.The bridging effect is enhanced and the growth of grain boundary cracks is inhibited,which is another reason for the gradual decrease of the alloys hot tearing susceptibility.As the Ni content gradually increased from 0 to 3.0 wt.%,the hot tearing susceptibility of Mg-6Y-(3-x)Zn-xNi alloys gradually decreased,and the CSC reached a minimum when the Ni content was 3.0 wt.%.The latent heat peak and precipitation temperature of the second phase in Mg-6Y-2Zn-1Ni,Mg-6Y-1Zn-2Ni,and Mg-6Y-3Ni alloys increase sequentially,which not only improves the ability to feed the residual liquid phase between the dendrites,but also the local temperature between the dendrites is increased,the solidification shrinkage stress generated during the solidification process is reduced,and the hot tearing susceptibility of the alloy is reduced.That is,Ni element has better resistance to hot tearing susceptibility than Zn element.