摘要
The actual effective partition coefficients of Mg and Cr in a cross-section of a dendrite arm in a direct-chill(DC)-casting ingot of 7475 aluminum alloy are obtained.Meanwhile,by analyzing the microstructure,the mechanism of the heterogeneous distribution of E(Al_(18)Mg_(3)Cr_(2))dispersoids in this DC ingot is revealed.The results show that the actual effective partition coefficients of Mg and Cr are 0.650 and 1.392,respectively,and they describe the heterogeneous distributions of Mg and Cr along the direction of radius of the cross-section of the dendrite arm of the alloy.After homogenization treatment at 470℃ for 24 h,Mg diffuses uniformly,but Cr hardly diffuses.Both the concentrations of Mg and Cr and the sites of heterogeneous nucleation in the alloy are the determinants of the formation of E dispersoids simultaneously.The heat treatment at 250℃ for 72 h provides a large number of the sites of heterogeneous nucleation of the formation of fine E dispersoids that will be formed in the center of the cross-section during the subsequent heat treatment at higher temperature.
研究7475铝合金半连续铸锭中枝晶臂横截面上镁元素和铬元素的实际有效分配系数。同时,通过微观结构分析,揭示E(Al_(18)Mg_(3)Cr_(2))弥散相在半连续铸锭中非均匀分布的机理。结果表明,镁和铬的实际有效分配系数分别为0.650和1.392,这些系数表明合金枝晶臂横截面半径方向上镁和铬的非均匀分布。经470℃均匀化处理24 h后,镁元素扩散均匀,而铬元素几乎不扩散。镁和铬的浓度以及合金中的异质形核位置同时是形成E弥散相的决定因素。250℃热处理72 h为大量细小的E弥散相在随后高温热处理过程中合金枝晶臂横截面心部的形成提供异质形核位置。
基金
financially supported by the National Natural Science Foundation of China(No.51871043)
Fundamental Research Funds for the Central Universities of China(No.N180212010)
Liaoning Natural Science Foundation of China(No.2019-MS-113)。
