Abstract
In this study, plasma electrolytic oxidation (PEO) was performed on Al and AlSi substrates using a pulsed direct current (DC) power source. The coating process was carried out in a Na2SiO3 electrolyte with the systematic change of pulse frequency (50–1400 Hz). The surface characteristics of the coatings were examined using scanning electron microscopy (SEM). The phase structure was characterized using X-ray diffraction (XRD). A differential scanning calorimeter (DSC) and a laser flash apparatus (LFA) were employed to test heat capacity and heat conductivity, respectively. Results showed that as the discharge frequency increased, the thermal physical properties of Al-PEO and AlSi-PEO coatings changed in different ways. At a high frequency, Al-PEO coatings had low porosity and were closed-pore structured whereas AlSi-PEO coatings had high porosity and large-size open-pore structures could be observed on their surfaces due to concentrated discharges. Based on these findings, it was found that the thermal productivity of coatings is closely correlated with the open-/closed-pore structure instead of porosity. PEO coatings with low heat capacity or low heat conductivity could be obtained with a controlled frequency.
Highlights
Improvement in the thermal efficiency of internal combustion engines plays a significant role in energy conservation and emission reduction, which is a major strategy adopted by the energy and power industries of countries across the globe [1,2,3]
The analysis reveals that the pore structure characterized by the coatings can reduce their heat capacity and heat conductivity and different pore morphologies have different impacts on both properties
Summary The following conclusions can be drawn from this work, which examines the effects of different pulse frequencies on the structure and thermal physical properties of Al-plasma electrolytic oxidation (PEO) and AlSi-PEO coatings
Summary
Improvement in the thermal efficiency of internal combustion engines plays a significant role in energy conservation and emission reduction, which is a major strategy adopted by the energy and power industries of countries across the globe [1,2,3]. Yttria-stabilized zirconia (YSZ) ceramic coatings have been widely used as thermal insulation coatings in the internal combustion engine sector [4,5,6], as they have superior properties of low heat conductivity and high fracture toughness, which can dramatically improve the piston top temperature as well as the combustion efficiency. YSZ ceramic coatings have low heat conductivity, their volumetric heat capacity is relatively high (>2500 kJ/(m3·K)) [7,8,9]. As a solution to this, coatings with low heat capacity are considered as a feasible way to increase internal combustion efficiency, as their surface temperature can decrease rapidly during the exhaust stroke, which can prevent the coatings from heating the air intake during the intake stroke [10]
Sign-in/Register to view highlights & summary 
Published Version (
Free)
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call