Solid-state recycling of AA6060 chips by hot extrusion is investigated. This study focuses on understanding the formation of oxides at the former chip boundaries, that could limit sound welding of the chips. The impact of the time and temperature of the annealing treatment prior to extrusion is analysed ex-situ by coupling TGA and XPS. The results show that for temperatures above 400 °C, oxidation kinetics follows a parabolic law. On top of the 10 nm Al2O3 native oxide layer, MgO islands first grow up to a thickness of 60 nm until reaching a covering rate of about 90 %, and then thicken. Limiting time and temperature of the annealing treatment is favourable to reduce oxide formation. During extrusion of the pre-compacted annealed chips, a new oxygen increase is measured. It results in larger oxides, with a thickness between 165 and 300 nm, depending on the annealing conditions. This enhanced oxidation combined with an increase of chip surface results in a covering rate of prior chip boundaries of 25 %. Extrusion was described into two sub-steps: first, densification of the chips in the billet occurs, during which oxides increase their covering rate if it was’nt yet saturated, or thicken; second, an elongation of the billet where oxides mostly grow on newly formed surfaces. A model using results from TGA, XPS, total oxygen concentration and TEM imaging is developed to quantitatively describe the sub-steps, to propose a complete description of the oxide network and to guide future selection of processing parameters.

中文翻译：

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退火对铝屑固态回收过程中氧化的影响


研究了通过热挤压对 AA6060 芯片进行固态回收的研究。本研究的重点是了解在以前的芯片边界处形成的氧化物，这可能会限制芯片的焊接声音。通过耦合 TGA 和 XPS 进行非原位分析挤出前退火处理的时间和温度的影响。结果表明，当温度高于 400 °C 时，氧化动力学遵循抛物线定律。在 10 nm Al2O3 天然氧化物层的顶部，MgO 岛首先长到 60 nm 的厚度，直到达到约 90% 的覆盖率，然后变厚。限制退火处理的时间和温度有利于减少氧化物的形成。在挤压预压实的退火片期间，测量到新的氧增加。它会产生更大的氧化物，厚度在 165 到 300 nm 之间，具体取决于退火条件。这种增强的氧化与芯片表面的增加相结合，导致先前芯片边界的覆盖率为 25%。挤压被描述为两个子步骤：首先，坯料中的切屑发生致密化，在此期间，如果尚未饱和或增厚，氧化物会增加其覆盖率;其次，坯料的伸长，氧化物主要生长在新形成的表面上。使用 TGA 、 XPS 、 总氧浓度 和 TEM 成像的结果开发了一个模型，以定量描述子步骤，提出氧化物网络的完整描述并指导未来加工参数的选择。