AZ31B镁合金凝固组织对室温力学性能的影响

Effects of Solidification Structure on Ambient Mechanical Properties of AZ31B Magnesium Alloy

采用铸锭底部喷水、侧面加热炉保温的方法制备了AZ31B镁合金铸锭。通过改变熔体过热温度来调整凝固组织,研究了凝固组织中晶粒大小以及形态对合金室温力学性能的影响。结果表明,采用这种方法制备的AZ31B镁合金铸锭,底部是柱状晶,其余为等轴晶。铸锭组织致密,无缩孔、缩松缺陷。当熔体过热温度由720℃提高到900℃时,铸锭底部柱状晶的长度由35mm减小到15mm,柱状晶间距由0.7mm减小到0.2mm;在距铸锭底部130mm处,等轴晶枝晶由0.8mm减小到0.1mm。减小等轴晶枝晶尺寸,可以提高试样的室温抗拉强度和塑性。垂直于柱状晶轴向进行拉伸时,试样的抗拉强度和伸长率与等轴晶相比明显下降。减小柱状晶间距,可以提高镁合金的室温压缩性能;当柱状晶间距相同时,垂直于柱状晶轴向进行压缩比平行于柱状晶轴向进行压缩的性能好。

AZ31B magnesium alloy ingots were prepared by spraying water towards the bottom ingot and holding at side face of the ingot using a heating-furnace.The solidification structure of magnesium alloy was modified through changing the melt superheating temperature,and effects of grain size and shape on ambient mechanical properties of AZ31B magnesium alloy were analyzed.The results show that the columnar crystals are generated at the bottom and the equiaxed crystal is at other location of ingot prepared using the method.Meanwhile,the structure exhibits dense with absence of shrinkage porosities（holes）.With melt superheating temperature increased from 720℃to 900℃,the length and spacing of columnar crystals are decreased from 0.8mm to 0.1mm,and from 0.7mm to 0.2mm,respectively.The equiaxed crystal size is decreased from 0.8mm to 0.1mm at 130mm position apart from the ingot bottom.The ambient tensile strength and plasticity are improved with decreasing in the equiaxed crystal size,especially for the plasticity.When the tension direction is perpendicular to the axial direction of columnar crystals,the tensile strength and elongation of the samples are obviously decreased compared with the equiaxed crystal.The ambient compression properties of magnesium alloy are increased with the decrease of the columnar crystal spacing.Under the same columnar crystal spacing conditions,the compression properties of perpendicular to columnar crystal axial direction are better than that of parallel to columnar crystal axial direction.