Mechanism of heterogeneous distribution of Cr-containing dispersoids in DC casting 7475 aluminum alloy
(1. School of Materials Science and Engineering, Northeastern University, Shenyang 110819, China;
2. Analytical and Testing Center, Northeastern University, Shenyang 110819, China;
3. Key Laboratory for Anisotropy and Texture of Materials, Ministry of Education, Northeastern University, Shenyang 110819, China;
4. Research Institute of BaoSteel, Shanghai 201900, China)
2. Analytical and Testing Center, Northeastern University, Shenyang 110819, China;
3. Key Laboratory for Anisotropy and Texture of Materials, Ministry of Education, Northeastern University, Shenyang 110819, China;
4. Research Institute of BaoSteel, Shanghai 201900, China)
Abstract: 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 (Al18Mg3Cr2) 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 °C 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 °C 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.
Key words: 7475 aluminum alloy; direct-chill-casting ingot; Al18Mg3Cr2 dispersoids; heterogeneous distribution; effective partition coefficient