Zinc and Aluminum hand in hand

Posted on by

It grows in Italy the use of wires of Zn / Al 85-15 in galvanizing electric arc spray.

The Zn / Al coating 85/15 It is composed of particles of Al wider and elongated surrounded by fine particles of pure Zn, Al forms an Al2O3 film on the surface that acts as a covering Zn. The coating offers a better resistance to corrosion of zinc or pure Aluminum combining the advantage of 2 metals species in the crevice corrosion (slots), or damaged surfaces.

Compared to pure zinc coating has the following major advantages:

  1. Low porosity (3%): the coating has fewer pores with smaller increasing the barrier effect and favoring the anchoring of paints;
  2. High Potential electro chemical and better sacrificial capacity;
  3. The present Aluminum acts as an inert coating, reducing the dissolution of zinc increasing the protection of the underlying steel with a consequent lengthening of the duration of the life cycle of the structure and reduction of the formation of white rust;
  4. The coating can remain as such without the need for sealants, It produces a more stable oxide of the pure zinc without the formation of blistering in immersion with slightly lower thickness zinc and far less than aluminum.
  5. The coating is densest (density 95%) 4,97 gr / cm³ and covers a greater surface area of ​​the 20-30% compared to pure Zn;
  6. Tear resistance equal to 7.000 Psi (electric arc) 4.000 Psi (flame). The adhesion increases with the application of a sealant;
  7. The application of a sealant increases the duration of the coating 40 years ( without duration sealants 25 years). The sealant should be applied immediately after spraying within 8 hours. They are epoxy-based, phenolic or polymers. Zinc is more galvanically active and provides increased cathodic protection in water compared to Aluminum. The Al with its oxides offers a greater resistance to abrasion.
  8. Melting Point 385 ˚C and this translates, during spraying, in a lower formation of over-spray, lower volume of dust and reduction of vapors of Zn;
  9. T ° sevizio 315 ° C against 60 ° C Zn pure making it applicable in steel tanks.
  10. Each pass of the operator corresponds to 50 μ thick;
  11. Good workability;

And 'excellent corrosion: NaCl and sulfur dioxide SO2 (bridges, highways, viaducts); It has a resistance to saline mist 10 times higher compared to pure zinc and corrosion at elevated temperatures up to 315 ˚C.

  1. The duration in atmosphere SO2 is 3000 hours equal to twice the pure zinc (1.500 hours)
  2. In aggressive agricultural environment (solid and liquid fertilizers KCL which liquid nitrogen) experience has shown that after 21 months of semi dipping a Zn / Al coating + painting shows a Zn reserve active 97-98% against 95% similar to the pure Zn coating. In nitrogen atmosphere, after 2 months of dipping seeds, the Zn / Al coating shows a metal active 93%, while the pure Zn coating, after 15 days presents a complete dissolution of Zn and formation of rust.

The application fields are: torri eoliche, offshore structures, truck chassis, agricultural machinery, grain silos, heat exchangers, electrical shielding, facings on longitudinal welds of profiled tubes Sendzimir rolling, etc..

In the lifetime of pipes it depends for 84% from Zn / Al coating and only for 15% by the thickness of the tube . In contact with the soil Zn slowly it turns into a dense layer, adherent, waterproof and continuous insoluble Zinc salts that constitute a protective screen . The pores activate the galvanic protection and healing promotes the formation of a stable layer and insoluble Zinc salts.

Do not get in Zn / Al 85/15 with wet cement, avoid contact until the cement has not formed because the Al is very reactive in an alkaline environment.