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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.
The influence of Mn on the hot cracking tendency in the solidification process of Mg-6.5Zn-xMn alloy was studied by means of an experimental device capable of accurately detecting and recording the microscopic changes of temperature, shrinkage displacement and shrinkage stress in the solidification process of magnesium alloy.The results show that, The proposed indexes of thermal cracking propensity evaluation, the larger the maximum shrinkage rate (vmax) and the stress accumulation coefficient (k), the greater the tendency of thermal cracking and the more obvious thermal cracking tendency when the high solid fraction appears. With the increase of Mn content , The vmax of Mg-6.5Zn-xMn alloys increases, but it appears to migrate to low solid fraction; k reaches the maximum at 0.35% Mn and appears at high solid fraction, leading to its tendency to crack The maximum of the thermal cracking of the alloy in the late solidification (high solid fraction) initiation and expansion, there is a clear grain filling channel between the low-melting phase in the late solidification liquid crystal surface in the film, The smaller the grain size, the smaller the thermal cracking tendency. The intergranular bridge formed by the interdendritic arms overlapping with each other after the dendrite separation strengthens the intergranular binding force at the late stage of the alloy solidification. However, Bridge will form a hot crack.