Metal finishing Q&As since 1989

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For the measurement of the adhesion strength of zinc coatings

2004

Dear Sir

The hardness and young's modulus across the zinc coating/steel interface have been measured with nano-indentation. But these can not be used to express the adhesion strength of interface.

The microstructure of hot dipping galvanized coating is normally different from that of galvanealling coating. The typical microstructure mainly consists of soft alpha Zn matrix, brittle zeta FeZn13 intermetallic, eta zinc bearing Fe2Al5 compound, when a small amount of Al added into the zinc bath (about 0.2wt%).

I try to use some strong glues to bond two zinc coated steel samples to remove the coatings, but I always fail to remove zinc coatings. The experiments includes sing lap tensile testing, four-point bending test, three point-bending test. It looks like a big problem. I guess the adhesion strength of coating is higher than 40 MPa. The bonding strength of normal glues is less than about 30 MPa, which results in the cracking of glue/zinc coating interface rather than coating/steel interface. My materials are zinc coated dual phase steels, zinc coated TRIP steels and zinc coated IF steels. The thickness of all zinc coatings are about 8-10 micro meter.

I wish to get the quantitative value of the adhesion strength. Any idea and suggestion is great appreciated.

Thanks in advance

Guim Song
NIMR - Delft, Delft, netherlands