Mn对Mg-6.5Zn合金热裂倾向性的影响  

EFFECT OF Mn ON HOT CRACKING TENDENCY OF Mg-6.5Zn ALLOYS

作　　者：李浩宇[1] 柏媛媛[1] 张海涛[1] 武鑫[1] 张志强[1] 乐启炽[1] 

机构地区：[1]东北大学材料电磁过程研究教育部重点实验室,沈阳110819

出　　处：《金属学报》2014年第10期1237-1243,共7页Acta Metallurgica Sinica

基　　金：国家重点基础研究发展计划资助项目2013CB632203~~

摘　　要：通过能够准确检测和记录镁合金凝固过程中温度、收缩位移和收缩应力细微变化的实验装置,研究了Mn对Mg-6.5Zn-xMn系合金凝固过程中热裂倾向性的影响规律.结果表明,所提出的热裂倾向性评价指标最大收缩速率(vmax)和应力累积系数(k)越大,热裂倾向越大,且其在高固相率出现时热裂倾向更显著;随Mn含量的增加,Mg-6.5Zn-xMn系合金的vmax增大,但其出现向低固相率迁移;k在Mn含量为0.35%时达到最大,且在高固相率时出现,导致其热裂倾向性最大.该系合金的热裂纹在凝固后期(高固相率)萌生并扩展,晶粒间存在明显的补缩通道;低熔点相于凝固后期在晶粒表面形成液膜,且液膜越厚,晶粒越细,热裂倾向性越小;枝晶分离后相互接触的枝晶臂搭接形成的晶间搭桥加强了合金凝固后期晶间结合力,但晶粒收缩受阻拉断晶间搭桥会形成热裂.Mg-Zn-Mn alloy has high hot cracking tendency（HCT）,but few researches focus on its hot cracking behavior and mechanism.The effect of Mn on the HCT of Mg-6.5Zn-xMn alloys was studied by the designed equipment which can measure and record the subtle changes of temperature,shrinkage displacement and shrinkage stress during solidification in this study.The results indicate that the larger the maximum contract rate（vmax） and the stress accumulating coefficient（k）,which are put forward to evaluate HCT,the higher the HCT is,and there is higher HTC when vmaxor k presents at high fraction of solid.The vmaxof Mg-6.5Zn-xMn alloy increases with the increase of Mn content,however its position move towards to lower fraction of solid,and the k reaches the maximum value and presents at high fraction of solid at 0.35%Mn,which means the greatest HCT in this composition.The hot cracks of these alloys initiated and propagated at final stage of solidification（with higher fraction of solid）,and the intergranular feeding channels could be observed.The thicker the liquid film around grains formed by the low melting point phases and the finer the grains,the less the HCT of the alloy is.After dendritic separation,interdendritic bridging formed by the jointing of dendrite arms could enhance the adhesive force between grains at final stage of solidification.However,the break of interdendritic bridging due to the hindrance to grain contraction would result in the hot cracks.

关 键 词：Mg-6.5Zn合金 MN 镁合金 热裂 

分 类 号：TG146.22[一般工业技术—材料科学与工程] TG113.26[金属学及工艺—金属材料]