| Because of its low density,high specific strength and high specific stiffness,magnesium alloy has wide application prospect in the field of light weight reduction and energy saving and emission reduction.However,the strength of magnesium alloy is low and the plastic forming ability is poor.It is the hotspot of magnesium alloy research whether to improve the comprehensive mechanical properties of magnesium alloy.The most effective way to improve the microstructure and properties of magnesium alloys is alloying.Therefore,based on the analysis of the present situation of improving the microstructure and properties of magnesium alloys,a new type of Zn-Mg-Ti master alloy was designed to improve the microstructure and mechanical properties of magnesium alloys.In this paper,the Zn-Mg-Ti master alloys were prepared by conventional casting method.The composition,phase morphology and element distribution of Zn-Mg-Ti alloy were studied.The influence of Zn-Mg-Ti master alloy on the microstructure of pure magnesium was studied systematically.Finally,the effects of Zn-Mg-Ti master alloy on the mechanical properties and corrosion properties of pure magnesium were studied.The work of the paper showed that when the composition of the second phase was different,the second phase morphology and element distribution were significantly different:（1）Zn82.6Mg12.8Ti4.6 master alloy mainly consists of MgZn2 and "flower-like" Zn-Mg-Ti ternary phase,the composition of different parts is different,Ti element is mainly distributed in the "petal" position,other parts without Ti;（2）Zn83Mg13.6Ti3.4 master alloy mainly by MgZn2 and “block-like” Zn-Mg-Ti ternary phase,in which Ti element is mainly concentrated in the block phase,the other parts without Ti element;（3）the melting point of Zn-Mg-Ti ternary phase in two kinds of master alloy are 720℃.The effect of Zn-Mg-Ti master alloy on microstructure of pure magnesium was investigated when the addition temperature of Zn-Mg-Ti alloy was 720℃ and the addition amount was 3%,5%,8% and 10% respectively.The results showed that:（1）with increase of the addition amount of Zn82.6Mg12.8Ti4.6 master alloy,the content of second phase in as-cast magnesium alloy increased gradually,the number of dendrites increased,and the morphology of second phase changed from Granular to strip.When the content of Zn82.6Mg12.8Ti4.6 master alloy was 8wt.%,The grain size of magnesium alloy was the finest,and with the increase of the addition amount of master alloy,the microstructure of the as-extruded magnesium alloy was continuously refined and the degree of dynamic recrystallization was improved;（2）with increase of the addition amount of Zn83Mg13.6Ti3.4 master alloy,the dendrites of cast magnesium alloy are gradually developed,the number of the second phase（Mg-Zn）increased gradually,and the second phase changed from point distribution to continuous reticular distribution.With the increase of the addition amount of Zn83Mg13.6Ti3.4 master alloy,the grain size of the heat-treated magnesium alloy decreased first and then increased.When the addition amount was 5%,the finest grain size could be obtained.Zn82.6Mg12.8Ti4.6 master alloy has a stronger grain refinment than Zn83Mg13.6Ti3.4 master alloy.Magnesium alloy grain refinement was mainly attributed to the solute atom titanium,which agglomerate at the front of solid-liquid interface lead to the constitutional supercooling and thus restrict the crystal to grow.The effect of Zn-Mg-Ti master alloy on the microstructure of pure magnesium was studied when the addition temperature was 8% and the addition temperature of Zn-Mg-Ti master alloy was 660℃,720℃ and 760℃ respectively.The results showed that:（1）with increase of addition temperature of Zn82.6Mg12.8Ti4.6 alloy,the second phase amount of as-cast magnesium alloy increased gradually,and the morphology of second phase changed from grain boundary distribution at low temperature to dispersion distribution at high temperature,and the grain size of the heat-treated magnesium alloy decreased first and then increased,and the grain size was the finest when the temperature was 720℃.（2）with the increase of addition temperature of Zn83Mg13.6Ti3.4 master alloy,the degree of dendriteization of magnesium alloy is increasing,grain size of heat-treated magnesium alloy gradually coarsening,the second phase distribution gradually dispersed,Ti elements gradually dispersed distribution,it was found that there was a cluster-like titanium-rich phase in the magnesium alloy when Zn83Mg13.6Ti3.4 master alloy added into pure magnesium,and the degree of agglomeration of the titanium-rich phase was weakened with the increase of adding temperature of Zn83Mg13.6Ti3.4 master alloy.The effects of Zn82.6Mg12.8Ti4.6 and Zn83Mg13.6Ti3.4 master alloys on the mechanical properties of as-extruded magnesium alloys and and corrosion properties of heat-treated magnesium alloys were investigated at room temperature.The results showed that:（1）when the addition amount of Zn82.6Mg12.8Ti4.6 was 8% at 720℃,the best mechanical properties could be obtained,the tensile strength and elongation of magnesium alloy were 308 MPa,21.5% respectively.This is related to the fine uniform microstructure of magnesium alloy and the second phases at grain boundary were less after addition content of Zn82.6Mg12.8Ti4.6 master alloy was 8% at 720℃.（2）the corrosion results showed that after soaking 42 h,when the addition amount of Zn82.6Mg12.8Ti4.6,Zn83Mg13.6Ti3.4 master alloy was 8% respectively at 720℃,the corrosion performance of magnesium alloy which contain 8% Zn82.6Mg12.8Ti4.6,Zn83Mg13.6Ti3.4 master alloy respectively were significantly better than commercial ZK60 magnesium alloy,but increase the immersion time,the corrosion performance of magnesium alloy which contain 8% Zn82.6Mg12.8Ti4.6,Zn83Mg13.6Ti3.4 master alloy respectively began to deteriorate. |
PDF Full Text Request