When liquid aluminum is exposed to air, an oxide layer instantaneously forms on the surface of the melt, which, when enfolded, becomes a double oxide film defect (bifilm), producing entrained air pockets forming voids, cracks, and areas of stress. Studies of the reactions between the air trapped inside the bifilms and the surrounding melt have produced reaction products such as AlN. In this study, examination of the fracture surfaces of an Al–7Si–0.3Mg (2L99) as-cast alloy revealed AlN apparently of a different “nodular” morphology of approximately 15 μm in length. In contrast to the “feather-shaped” AlN morphology grown through holding in nitrogen or the addition of Mo to 2L99 observed in previous research, the observed nodular morphology in this study was thought to be less permeable. This confirmed the hypothesis of Nyahumwa et al. (AFS Trans 106:215–223, 1998), who suggested that the entrapped air in bifilms can react with the surrounding liquid melt by initially consuming oxygen to form oxides, such as spinel (MgAl₂O₄), followed by the consumption of the nitrogen to form AlN. The AlN observed has been proposed to reduce the size of bifilms and correspondingly improve the mechanical properties of the alloy. In this work, AlN was also grown by holding alloys in a controlled nitrogen gas environment at 850 °C at various holding times to reveal AlN morphologies.

当液态铝暴露在空气中时，熔体表面会立即形成氧化层，当其被折叠时，会形成双氧化膜缺陷（双膜），产生夹带的气穴，从而形成空隙、裂纹和应力区域。对双膜内空气与周围熔体之间反应的研究已经产生了反应产物，例如 AlN。在这项研究中，对 Al-7Si-0.3Mg (2L99) 铸态合金的断裂表面进行检查，发现 AlN 明显具有不同的“结节”形态，尺寸约为 15  μ米长。与之前研究中观察到的通过保持氮气或向 2L99 添加 Mo 生长的“羽毛状”AlN 形态相比，本研究中观察到的结节形态被认为渗透性较差。这证实了 Nyahumwa等人的假设。(AFS Trans 106:215–223, 1998)，他提出双膜中截留的空气可以与周围的液态熔体发生反应，首先消耗氧气形成氧化物，例如尖晶石 (MgAl ₂ O ₄），然后消耗氮气形成AlN。观察到的 AlN 被认为可以减小双膜的尺寸并相应地提高合金的机械性能。在这项工作中，还通过在 850 °C 的受控氮气环境中保持合金并在不同的保持时间下生长 AlN，以揭示 AlN 形态。