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Thermal spraying aluminum coatings have been widely used in the corrosion protection of mild steel in seawater. In this study, high-efficiency supersonic plasma spraying (HESP) and oxygen–acetylene flame spraying (FS) were used to prepare aluminum coatings. The micromorphology of the coatings was analyzed by a scanning electron microscope equipped with an energy-dispersive x-ray spectrometer. The phase identification of the coatings was conducted by an x-ray diffractometer. The Vickers hardness and bonding strength of the coatings were measured by an HMV-2000 Vickers hardness tester and MTS809 universal tensile tester. The corrosion resistance of the coatings was tested by an IM6ex electrochemical workstation. The results show that the aluminum coatings prepared by HESP have a denser structure, higher microhardness, higher bonding strength, and better corrosion resistance than those prepared by the traditional FS. After 480-h immersion in 3.5 wt.% NaCl solution, a dense corrosion product formed on the surface of aluminum coatings prepared by HESP prevents further corrosion of the coatings, but the aluminum coatings sprayed by FS demonstrate a serious pitting phenomenon.

Hypereutectic Al-Si alloy is an ideal surface strengthening material for aluminum alloy cylinder body. However, the coarse eutectic silicon phase and primary silicon particles in Al-Si alloys prepared by traditional methods lead to poor mechanical properties of the alloys, and the high cost of preparation limits the practical application of hypereutectic Al-Si alloys. In this study, Al-25 wt.%Si coatings were prepared on substrate 7075 by high-efficiency supersonic plasma spraying (HESP). The micromorphology, Vickers hardness, bonding strength and wear resistance of the coatings were measured and characterized by experiments. The results show that the Al-25 wt.%Si coatings prepared by HESP have a denser structure, and the primary silicon phase in the coatings is refined. The hardness of the coatings is 235 HV0.1, and the bonding strength between the coatings and the substrate is 44.1 MPa. The wear rate of the coatings is reduced by 20 times compared with that of the substrate, and the wear mechanism is mainly adhesion wear and oxidation wear.

Plasma-sprayed ceramic coatings have been widely used in friction and wear protection of mechanical parts. In this paper, the nanostructured Al2O3–13 wt% TiO2 coatings were prepared by high-efficiency supersonic plasma spraying (HESP) and atmospheric plasma spraying (APS), respectively. The surface and section morphology of the coatings were observed by scanning electron microscopy (SEM). The phase composition of the coatings was analyzed by X-ray diffraction (XRD). The dry sliding friction properties of the coatings were tested on UMT-3 friction and wear testing machine. The results show that after plasma spraying, a large amount of γ-Al2O3 phase appears, while the TiO2 phase almost disappears in the coatings; compared with APS, the coatings sprayed by HESP have fewer defects and better coating quality; under dry friction condition, the steady-state friction coefficient of the coatings sprayed by HESP and APS all decreases with the increase of load, and the wear volume all increases with the increase of load. When the load is more than 40 N, wear volume of the coatings sprayed by APS is basically twice that of HESP; the wear mechanism of the coatings sprayed by HESP is the laminar cracking, peeling off and the adhesive wear.