两步法变质处理Zn-6Al合金的显微组织和力学性能研究

Microstructure and Mechanical Properties of Zn-6Al Alloy Prepared by Two-Step Modification

采用Al-5Ti-B对Zn-6Al合金进行两步法变质处理,运用扫描电镜(SEM)、能谱仪(EDS)和万能试验机分析测试了变质处理前后Zn-6Al合金的凝固组织和力学性能。结果表明:当加入0.50%的Al-5Ti-B时,随着高温变质熔体占比的增加,Zn-6Al合金中初生β-Al相面积分数不断增加,共晶组织层片间距先减小再增加;Zn-6Al合金的抗拉强度与屈服强度不断增加,延伸率先增加后降低;当高温变质熔体与低温熔体质量比为2∶3时,Zn-6Al合金的综合力学性能最佳。当高温变质熔体与低温熔体质量比为2∶3时,随着Al-5Ti-B加入量的增加,Zn-6Al合金中初生β-Al相面积分数、抗拉强度、屈服强度和延伸率呈现先增加再降低的变化趋势,共晶组织则呈现先细化再粗化的变化趋势。与未进行变质处理的Zn-6Al合金相比,当高温变质熔体与低温熔体质量比为2∶3和Al-5Ti-B加入量为0.75%时,Zn-6Al合金的抗拉强度、屈服强度和伸长率分别增加24%,13%和118%。采用Al-5Ti-B对Zn-6Al合金进行两步法变质处理,可明显提高Zn-6Al合金的综合力学性能。

With its excellent fluidity and mechanical properties,Zn-Al alloy is widely used in automobile manufacturing,daily hardware and other industrial fields.As the price of zinc ingot is higher than that of aluminum ingot,the aluminum content of YZZnAl4A alloy can be increased to 6 wt.%,thus reducing the preparation cost of the alloy.The modification of Zn-Al alloy can improve its microstructure and mechanical properties,but the modification of Zn-Al alloy with Al-5Ti-B is not good due to the high melting point of the modifier.In this paper,part of the high temperature modification Zn-6Al alloy melt was used to modify the low temperature Zn-6Al alloy melt.The problem of poor modification effect of Al-5Ti-B on Zn-Al alloy was solved,and the microstructure and mechanical properties of Zn-6Al alloy were obviously improved.The raw materials of Zn-6Al alloy were pure Al(99.85%),ZX01(3.9%~4.3%Al and 0.03%~0.06%Mg with zinc allowance),commercial Al-5Ti-B alloy was used as modifier.The methods of metallographic microscope,scanning electron microscope(SEM),energy spectrometer(EDS),universal tensile test was employed to analyze the organization characteristics and mechanical properties of zinc alloy,and the effect of mass ratio of high and low temperature melt on microstructure and mechanical properties of Zn-Al alloy was discussed.By analyzing the microstructure and mechanical properties of Zn-6Al alloy,the optimal mixing ratio of high and low temperature melt and the optimal addition amount of Al-5Ti-B modifier was determined.The results showed that Al-5Ti-B as difficult to melt into the melt during the modification of Zn-6Al alloy at 430℃,and the microstructure and mechanical properties remained unchanged compared with those without modification.When Zn-6Al alloy was modified at 600℃,primary β-Al phase increased significantly in the solidified microstructure of the alloy,but there were many small holes or oxides on the tensile fracture,which greatly reduced the mechanical properties of the alloy.When the mass ratio of high temperature metamorphic melt to low temperature melt was 1∶4,the microstructure of Zn-6Al alloy was mainly composed of gray black β-Al which surrounding gray whiteη-Zn and fine lamellarα-Al+η-Zn eutectic structure.Primaryβ-Al was relatively thick and the dendrite characteristics were obvious.With the increase of high temperature metamorphic melt,the size of primary β-Al phase decreased,and the dendrite characteristics of primary β-Al phase decreased obviously,and the thickness and spacing of β-Al lamellar in eutectic structure decreased continuously.When the mass ratio of high temperature melt to low temperature melt was increased to 2∶3,the roundedness of primary β-Al particles increased and the size of primary β-Al particles was the minimum.Compared with the mass ratio of high temperature melt to low temperature melt of 1∶4,the lamellar spacing decreased by 37.5%,and the metamorphic effect reached the best state.When the mass ratio of high temperature melt to low temperature melt increased to 1∶1,primary β-Al phase was slightly coarsened and the thickness and spacing of β-Al lamellar in eutectic structure increased obviously.The tensile strength and yield strength of Zn-6Al alloy increased with the increase of the mass ratio of high temperature metamorphic melt,while the elongation of Zn-6Al alloy showed a trend of first increasing and then decreasing.The cleavage plane of Zn-6Al alloy showed a trend of becoming fine and then coarser.When the mass ratio of high and low temperature melt was 2∶3,the elongation reached the maximum value of 1.6%.The cleavage plane of Zn-6Al alloy was the smallest,and there were more dimples and tear ridges increase obviously.When the mass ratio of high and low temperature melt was 2∶3,the number and area fraction of granular primary β-Al phase in Zn-6Al alloy increased with the increase of Al-5Ti-B addition,and the morphology changed from dendrite to granular,and the eutectic microstructure was refined.When the amount of Al-5Ti-B was 0.75%,the granular primary β-Al phase could reach the maximum value of 23.4%,the size was small and the distribution was uniform,and β-Al phase in eutectic structure changed into short coarse sheet and granular.When the amount of Al-5Ti-B increased to 1.00%,the number of granular primary β-Al phase decreased,the phase size increased,the eutectic structure changed to lamellar structure,β-Al phase lamellar thickness,the lamellar spacing increased.With the addition of Al-5Ti-B,the tensile strength,yield strength and elongation of Zn-6Al alloy increased first and then decreased.When the mass ratio of warm metasomatic melt to low temperature melt was 2∶3 and the addition of Al-5Ti-B was 0.75%,the tensile strength,yield strength and elongation of Zn-6Al alloy increased by 24%,13%and 118%,respectively.With the increase of Al-5Ti-B addition,the number of cleavage planes on the tensile fracture of Zn-6Al alloy increased and its size decreased,and more dimples appeared while the number of ridged ridges increased.When the amount of Al-5Ti-B was 0.75%,there were many fine cleavage steps and tear ridges on the tensile fracture of Zn-6Al alloy,and there were also many dimples of different sizes and depths.The alloy exhibited a brittle and ductile mixed fracture mode.When the addition amount of Al-5Ti-B increases to 1.00%,the cleavage plane on the tensile fracture of Zn-6Al alloy began to coarser,and the tearing ridge became coarser and longer.