采用Al-4.5Cu单晶进行台阶变速定向凝固实验，考察了金属合金中一次枝晶间距随凝固生长速度变化的动态响应规律.结果表明，对于确定的凝固控制参数，稳态一次枝晶间距选择一个较宽的容许分布范围；同时，平均一次间距的选择也是与凝固系统所经历的历史显著相关实验结果很好地支持了Hunt－Lu提出的枝晶生长一次间距的下限模型．
In unidirectional solidification of Al-4.5Cu alloy,history-dependent selection of the primary dendritic spacing is systematically investigated by the experimental method of step-variation in growth rate. A single crystal is formed in the sample before each experimental run, so that the influence of crystal boundary on the primary spacing is avoided. It is found that the primary dendritic spacing is remarkably history-dependent in the metallic alloy as in the transparent model alloy. The average primary spacing is dependent not only on the current growth conditions as described in the previous models, but also on the way those conditions were achieved remarkably. There exists a wide allowable range of primary spacing for given growth conditions. The lower limit obtained experimentally is compared with that calculated theoretically with the Hunt-Lu model, which shows excellent fit between them.
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