The soft sparking regime of Plasma Electrolytic Oxidation (PEO) of valve metals attracts increasing attention as it enables a better process control with improved energy efficiency and coatings with enhanced performance to be obtained. Here, the discharges softening phenomenon was characterised by evaluation of changes in electrical signal, composition of gaseous products and morphology of the metal-oxide interface in PEO coatings on Al. The coatings were formed using two electrical regimes retarding or promoting soft sparking conditions. Harmonic analysis of PEO process has been performed using independent evaluation of the positive and negative half-waves of polarisation signal. The composition of gas evolved during the PEO process was evaluated by a quantitative gas analyser. Coatings were characterised by scanning and transmission electron microscopy with energy dispersive spectroscopy and small area electron diffraction. It was found that discharge softening is accompanied with a decrease in oxygen evolution rate, an increase in equivalent capacitance of anodic process as well as structural and compositional changes near the metal-oxide interface. The experimental findings provide further support to the explanation of discharge softening phenomenon by narrowing the active zone at the metal-oxide interface due to intercalation of hydrogen species into anodic alumina under cathodic polarisation. Such mechanistic understanding allows rational regime selection, in-situ process control and optimisation of the coating properties to be performed that paves the way to intellectual manufacturing approach based on careful process monitoring in operando.

阀金属的等离子电解氧化 (PEO) 的软火花机制引起了越来越多的关注，因为它可以实现更好的工艺控制，提高能源效率，并获得性能增强的涂层。在这里，放电软化现象的特点是评估电信号的变化、气体产物的组成和铝上 PEO 涂层中金属氧化物界面的形态。涂层是使用两种延迟或促进软火花条件的电气方案形成的。使用极化信号的正负半波的独立评估来执行 PEO 过程的谐波分析。通过定量气体分析仪评估 PEO 过程中产生的气体成分。涂层通过扫描和透射电子显微镜与能量色散光谱和小面积电子衍射进行表征。发现放电软化伴随着析氧速率的降低、阳极过程等效电容的增加以及金属-氧化物界面附近的结构和成分的变化。实验结果进一步支持了放电软化现象的解释，即由于在阴极极化下氢物种嵌入阳极氧化铝中，金属-氧化物界面处的活性区变窄。这种机械理解允许理性的政权选择，