Characterization and Behaviour of Non-metallic Inclusions in Molten State 5xxx Alloy

The constantly high consumption rate of 5xxx alloys leads to prevalence of high Mg-containing, thin-gauged scraps in the recycling market. Compared with the extensive research efforts devoted on increasing metal yield during remelting process, melt cleanliness of secondary Al-Mg melt attracted only limited attention. In the pursuit of producing primary-quality 5xxx alloys with secondary sources, the control of inclusions plays a decisive role. Any effort to remove inclusions must rely firstly on sound information of their characteristics in the melt. From removal perspective, it is beneficial that other efficient inclusions removal processes can be deployed and orchestrated with conventional sedimentation and filtration processes so that the melts loaded with high amount of inclusions and/or fine particles can be well handled. During the search of such efficient processes, EM processing and degassing process comes into our radar.

In the first part of this study, inclusions present in as-remelted 5182 alloy were characterized to give comprehensive information of inclusions in the secondary 5xxx melt. As a follow-up, electromagnetic (EM) processing realized via induction crucible furnaces (ICFs) was experimentally demonstrated to be advantageous for rapid separation of inclusions. The enhanced separation rate can be realized via the inherent strong particle EM force and/or promotion of hetero-agglomeration between coarse and fine inclusions (the "scavenging" concept). In the last part of the study, the amount variation of inclusions during Cl2-free degassing treatment was assessed and the focus was mainly put on results interpretation from perspective of inclusions separation, fragmentation, and interactions.