INFLUENCE OF PLASMA-ELECTROLYTIC OXIDATION PROCESS TECHNOLOGICAL PARAMETERS OF ALUMINUM ON COATING GROWTH RATE

There has been carried out an analysis of methods of oxide covering formation productivity increasing during plasma electrolytic oxidation of aluminum in electrolyte. There has been developed a technology of blank manufacturing and part strengthening by plasma electrolytic oxidation in the electrolyte, as well as the workbench has been modernized. There has been studied the process of oxidoceramic coating synthesis for the D16T aluminum deformed alloy of during plasma electrolytic oxidation in the electrolyte for different process parameters. It is established that the growth rate of oxidoceramic coating can be significantly increased by electrolyte component concentration involved in aluminum oxidation and rational choice of process electrical parameters. Hydrogen peroxide addition leads to obtained oxoceramic coating thickness increasing due to O, O2, OH, OH– concentration increasing in the electrolyte. It is established that the optimal concentration of H2O2 ranges from 5 g/l to 7 g/l. A further increase of peroxide concentration leads to a decrease in peroxide effect on oxoceramic coating growth rate on the D16T aluminum deformed alloy due to pH changes of the electrolyte and the deterioration of the oxide coating.

Factors of quality increase in protective chromium coatings on aluminum alloys obtained through pyrolytic precipitation

There are considered the problems of control parameter detection in the process of pyrolytic chromium coatings on aluminum alloy and the investigation of their impact upon coating structure, strengthening indices, adhesion strength, and also upon kinetics of coating growth. The investigations have shown that the method mentioned is promising for aluminum alloy surface strengthening, and also it allows obtaining chromium coatings with high hardness and thick constant possessing increased wear-resistance.

Evolution of the Microstructure and Properties of Pre-Boronized Coatings During Pack-Cementation Chromizing

The effect of chromizing time on the microstructure and properties of B–Cr duplex-alloyed coating prepared by a two-step pack-cementation process was investigated. The phases, microstructure, and element distribution of three coatings obtained were characterized by X-ray diffraction (XRD), secondary electron imaging (SEI), backscattering electron imaging (BSEI), and energy dispersive spectroscopy (EDS), respectively. The results show that as the chromizing time increases, the net-like Fe2B and rod-like CrFeB phases in the coating gradually disappear, and finally completely transform into the block-like Cr2B and CrxCy (Cr7C3 and Cr23C6) phases. The growth kinetics analysis shows that interface reaction dominates the coating growth during the early stage of chromizing, while atomic diffusion gradually controls the coating growth at the later stage. The evolution mechanism of the B-Cr duplex-alloyed coating was also discussed.

INVESTIGATION OF THE INFLUENCE OF COMPONENT COMPOSITION OF PEO ELECTROLYTES ON THEIR STABILITY AND COATING PROPERTIES

The efficiency of various variants of the component composition of alkaline electrolytes of plasma electrolytic oxidation (PEO) was studied. Technical liquid glass, NaOH, Na2B4O7, Na3PO4, and NaAlO2 were used as components of aqueous solutions. All of the studied components of electrolytes are the most common for use in PEO processes of aluminum alloys. The influence of the component composition of electrolytes on their stability during 30 days of exposure was evaluated, and the most stable compositions were selected. The structure and properties of coatings formed on samples of aluminum alloy AK6 during PEO are studied. The dependences of the hardness of coatings and their growth rate on the composition of the electrolyte are established. Possible variants of coating growth in the PEO process with different component composition of electrolytes are proposed.