Investigation of AlSi coatings prepared by laser-assisted atmospheric plasma spraying of internal surfaces of tubes

Laser-assisted atmospheric plasma spraying (LAAPS) is a new one-step coating process performed in air whereby the laser beam interacts with the plasma torch at the substrate or coating surface during deposition to generate a coating that is metallurgically bonded to the substrate. This hybrid process was developed in order to combine the specific advantages of APS and laser cladding. In this paper, the development of a hybrid gun for coating internal surfaces of tubes and cylinder bores by LAAPS is presented. The process was optimized for spraying AlSi30 coatings on internal surfaces of aluminum alloy cylinder bores. Single-pass coatings with thicknesses of 300-400 mu m and metallurgical bonding to the substrates can be realized by applying an optimized parameter set. The dependence of coating microstructure on spray parameters was investigated by metallographic preparation and optical microscopy. Surface pretreatment must be performed to eliminate the strongly adhering oxide layer on the aluminum alloy substrate and to attain metallurgical bonding of coating to substrate.