Effects of high pressure water jet on aluminum surfaces prior to thermal spray coating

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Virginia Tech


Most thermal spray coating processes can be divided into three sub-processes; substrate surface preparation, the thermal spray operation and a post-coating surface finishing operation such as honing or grinding. Reliable and robust surface preparation is needed to guarantee maximum coating adhesion to substrates. Traditionally, the grit blasting process is used for surface preparation of materials receiving a thermal spray coating. However, in high volume production, the reproducibility of surface topography decays with time as grit particles are recycled through surface preparation operation. The focus of this project is to enhance the coating's ability to adhere to an aluminum substrate by incorporating high pressure water jet as a surface preparation operation.

Water pressure, standoff distance, number of orifices, orifice size and rotation speed are process parameters identified as having an effect on surface roughness and coating adhesion strength. Through classical statistical analysis, main effects as well as 2 and 3 factor interactions are revealed and studied.

A direct and significant relationship exists between water pressure, standoff distance and number of orifices. Correlation exists among adhesion strength and surface roughness parameters Ra, Rq and Rtm, respectively. Recommendations are made for further investigation into reducing water pressure and rotation speed requirements while sustaining the same level of surface modification.



post-coating surface, substrate surface preparation, thermal spray